THE BIG CUBIC-INCH TURBO BLOG

2017 Test

noreply@blogger.com (Editor) — Mon, 20 Feb 2017 17:44:00 +0000

2017 test

SCALING, PART I: ARE TURBOCHARGERS A REPLACEMENT FOR DISPLACEMENT?

noreply@blogger.com (Editor) — Sat, 23 Apr 2011 13:38:00 +0000

By 460-BBF-Turbo-In-CC (adapted from the legendary Car Craft Forum turbo blog)

"There's no replacement for displacement." -- Old Car Crafters' saying

Much of the writing on turbocharging is based on the assumption that turbocharging is a "replacement for displacement."

Are turbos really a substitute for cubic inch displacement? The answer is: "it depends."

Most certainly if fuel octane is virtually unlimited and engine life is measured in hours or minutes rather than hundreds of thousands of miles, turbocharged small engines have often proven much more powerful than naturally-aspirated big-cube powerplants.

And when street horsepower outputs are modest (less than 600 h.p.) turbocharging often stands in very well for large cubic inch mills.

But what about when lofty horsepower goals must be accomplished with durability and on widely available pump fuels? Is a small turbocharged engine going to be enough? Or will turbocharging need the added "boost" of extra cubes? And what are the downsides to hauling around a larger turbo 'plant?

These are questions that we need to answer before going much further in the turbo selection process.

One way of looking at the problem is through "scaling." "Scaling" in this context is taking proven test data from another project and extrapolating it to a variety of engine sizes for rough comparisons.

Of course this form of "scaling" is not completely accurate because of many factors. Small-bore engines may be stronger and more detonation resistant than larger-bore lumps. Volumetric efficiencies may significantly vary across engine types and sizes. Comparison engines may not be able to "live" under as much cylinder pressure as the original test engine.

But acknowledging these limitations, scaling can provide a "ballpark" figure about what outputs are realistic.

Nelson and Freiburger's "F-Bomb" Camaro provides a good baseline for a scaling exercise. While the "F-Bomb" engine is hardly a grassroots build, published test data is available for a wide range of r.p.m. and manifold pressures.

The first step in scaling is converting the raw data into a factor that can be multiplied by the displacement of the comparison engines. The process is simple and quick on a computer spreadsheet or calculator. First, divide the horsepower output by test engine size. Then multiply the resulting factor by the comparison engine size.

For simplicity, we'll use horsepower per liter (hp/l) as the factor.

The first published data set for the "F-Bomb" engine is a safe "low-boost" test (6.3-7.0 psi)

RPM HP hp/l

3500 418 62.80

3600 434 65.21

3700 454 68.21

3800 475 71.37

3900 498 74.82

4000 520 78.13

4100 539 80.98

4200 558 83.84

4300 574 86.24

4400 588 88.34

4500 605 90.90

4600 625 93.90

4700 644 96.76

4800 661 99.31

4900 670 100.67

5000 680 102.17

5100 695 104.42

5200 705 105.92

5300 718 107.88

5400 727 109.23

5500 730 109.68

5600 738 110.88

5700 744 111.78

5800 751 112.83

5900 761 114.34

6000 769 115.54

The next data set is what DF suggested was the at the limit for pump gasoline with the "F-Bomb's" charge-cooled EFI engine (11.0-14.4 psi)

RPM HP hp/l

3500 524 78.73

3600 559 83.99

3700 600 90.15

3800 638 95.86

3900 673 101.12

4000 705 105.92

4100 732 109.98

4200 753 113.14

4300 768 115.39

4400 787 118.24

4500 808 121.40

4600 822 123.50

4700 842 126.51

4800 873 131.17

4900 901 135.37

5000 927 139.28

5100 950 142.73

5200 967 145.29

5300 981 147.39

5400 991 148.89

5500 991 148.89

5600 997 149.80

5700 1008 151.45

5800 1025 154.00

5900 1022 153.55

6000 1009 151.60

The next data set is a moderate pull on race gas (12.2-18.3 psi).

RPM HP hp/l

3500 560 84.14

3600 600 90.15

3700 652 97.96

3800 709 106.52

3900 755 113.44

4000 778 116.89

4100 809 121.55

4200 834 125.31

4300 854 128.31

4400 874 131.32

4500 896 134.62

4600 921 138.38

4700 948 142.43

4800 979 147.09

4900 1004 150.85

5000 1028 154.45

5100 1059 159.11

5200 1080 162.27

5300 1087 163.32

5400 1103 165.72

5500 1120 168.28

5600 1139 171.13

5700 1150 172.78

5800 1155 173.53

5900 1161 174.44

6000 1165 175.04

By way of comparison, the turbocharged "Low-Buck" Demon 454 BBC in the February 2011 issue of Car Craft yields the following test factors:

RPM HP hp/l (hp/7.4)

3500 443 59.86

4000 527 71.22

4500 619 83.65

5000 696 94.05

5500 743 100.41

6000 776 104.86

6400 767 103.65

It's clear that the Nelson/Freiburger engine is much more efficient than the non-charge cooled, single-turbo "Low-Buck" 454. This could be the result of several factors including turbo efficiency, ignition timing, intake charge temperature and density, and volumetric efficiency.

FIRST PRINCIPLES: A PRIMER ON TURBOCHARGER ENERGY USE

noreply@blogger.com (Editor) — Sat, 23 Apr 2011 13:18:00 +0000

By 460-BBF-Turbo-In-CC (adapted from the legendary Car Craft Forum turbo blog)

"Energy can be neither created nor destroyed. It can only change forms." -- First Law of Thermodynamics (abridged)

Many Car Crafters first learn about this through the Bernoulli Principle, as applied to carburetion. Speeding up air through a narrower passage (a carburetor's venturi) lowers the pressure of the air stream and allows outside air pressure (through the fuel bowl vents) to force fuel through the metering system into the venturi air stream. In other words, Pressure energy is briefly exchanged for velocity energy.

Changing energy into different forms is also at the core of how turbocharging works. Pressure, velocity and temperature of the gas passing through the compressor and turbine are interrelated and change predictably at different points of the turbocharging process.

For example, the compressor impeller increases the velocity of the intake air by pumping it through its blades at a high r.p.m. This air velocity energy is then tranformed into stable flow and higher pressure through the diffuser section of the compressor housing. Although some energy is converted into heat, the bulk of the energy input has transformed from rotational energy into increased air pressure.

Remember that the difference between the outside air pressure and the post-compressor air pressure is called the pressure ratio.

More energy is, of course, added to the system through the combustion process. Thus, on the turbine side, the hot, pressurized and pulsing exhaust gas is accelerated through a volute in the turbine housing(think: funnel bent around a circle) to a nozzle. The exhaust's expansion from the nozzle through the turbine blades to the low-pressure exhaust rotates the turbine, converting velocity energy and sometimes pulse energy into the rotational force that powers the compressor.

READING TURBO COMPRESSOR MAPS, PART IV: EFFICIENCY ISLANDS

noreply@blogger.com (Editor) — Sat, 23 Apr 2011 13:11:00 +0000

By 460-BBF-Turbo-In-CC (adapted from the legendary Car Craft Forum turbo blog)

"Efficiency is doing things right." -- Peter Drucker

Anyone who has mistakenly put their hand on the shop compressor discharge line will always remember that compressing air results in heat. And NASCAR TV viewers often hear about "starting on low tire pressures" to avoid "pressure build-up."

Both of these are examples of the relationship between air volume, air pressure and air temperature.

Ideal gas law states that:

(air pressure x air volume)/air temperature = remains constant (Miller 19-20) Thus, increases in air pressure of a fixed quantiy of air result in increases in temperature.

When any compressor takes a "gulp" of air and compresses it into a smaller space, heat is necessarily produced. Often, the temp increase is explained as the result of increased friction between air moleules rubbing together when jammed into a smaller space.

Engineers and scientists describe the ideal temperature rise from air compression as "adibatic" -- neither gaining or losing any heat (beyond what the Ideal Gas Law predicts, that is).

However, no air compressor is 100% efficient. Internal air movement, impeller friction, pumping losses, and other inefficiencies add extra heat to the compressed air. This inefficiency is represented on turbo compressor maps and is critical to determining the actual density of the compressed charge.

Looking at the old T66 turbo map, the lines in the middle of the map show zones or "islands" of efficiency. The percentages shown are the calculated efficiency of the compressor, based on measurement of the discharge temperature of the compressed air.

Thus, when someone reports that a particular compressor is operating in the 75% efficient zone at a particular pressure ratio, they're saying that the compressor is heating the air 25% MORE than the Ideal Gas Law adibatic temperature rise formula predicts.

By way of comparison, when a traditional Roots blower is operating in a 50% efficiency island, then it is heating the air 50% more than the ideal temp rise formula predicts.

Extra heat in the compressor discharge air indicates two things. First, the extra heaing means that the dischared air is less dense than under ideal conditions. Second, the extra heat shows that not all of the "work" applied to compressing the air actually resulted in air compression -- some of the energy was "lost" to heating the compressed air. (engineers and scientists refer to this as "isentropic efficiency.")

However, for Car Crafters, the more important things are to determine how much density has been lost and how to recover as much of it as possible.

WHAT IS "PRESSURE RATIO?" (AND HOW ALTITUDE AND RESTRICTIVE AIR INTAKES AFFECT IT)

noreply@blogger.com (Editor) — Sat, 23 Apr 2011 13:01:00 +0000

By 460-BBF-Turbo-In-CC (adapted from the legendary Car Craft Forum turbo blog)

"The course of the flight up and down was exceedingly erratic, partly due to the irregularity of the air . . . . " -- Orville Wright

Some readers have probably wondered why turbo maps use "pressure ratio" instead of "boost" (manifold pressure).

The simple answer is that reductions in compressor inlet pressure without any change in the pressure ratio will lead to reductions in manifold pressure.

Conversely, if manifold pressure stays constant and inlet pressure decreases, the pressure ratio must increase. formula to "prove" this is found in virtually every turbocharger matching book, from the Hugh MacInnes "classic" Turbochargers to the latest books from Miller, Hartman, and Warner.

Pressure ratio = (boost pressure (gauge pressure) + ambient air pressure)/ambient air pressure.

(See MacInnes at 16, Miller at 39, Warner at 23, A. Graham Bell at 68, Corky Bell at 26)

So how does this really work: If you're testing a car on the beach (at sea level), the average barometric pressure reading should be ~ 14.7 psi (29.92 in. Hg.) Now if the "gauge pressure" indicates 30 psi of "boost" . . .

Pressure Ratio = 30 + 14.7 / 14.7

Pressure Ratio = 44.7/14.7

And when you plug these numbers into your handy calculator or computer spreadsheet, you get 3.04. Thus,

Pressure Ratio = 3.04:1

That means you've crammed three "atmospheres" into the space of one. (You get one for free and two more from the turbo)

Now run the same calculation a little more than 2/3s of the way up Pikes Peak at 10,000 ft.

Average barometric pressure reading: 10.1 psi (20.58 in. Hg.) (A. Graham Bell summarizes you lose ~ 0.5 psi ambient air pressure for each 1,000 ft. increase in altitude.)

Pressure Ratio (10,000 ft) = 30 (gauge pressure) + 10.1/10.1

Pressure Ratio (10,000 ft) = 3.97:1

WHAT! How can that be? To produce 30 psi in the thin air of 10,000 ft., the turbo compressor had to work much harder. The pressure ratio had to increase to keep the "gauge pressure" constant.

But what if the pressure ratio hadn't increased? "Gauge pressure" would have dropped to 20.2 psi.

What should be obvious here is that a chart which equates pressure ratio to "boost" only works at a specific altitude. Most such charts assume sea level ambient air pressure.

This also illustrates a flaw in a fixed linking of compressor speed to engine r.p.m., as belt-driven superchargers do. Recalling the general relationship between pressure ratio and compressor r.p.m., a turbo can speed up to to increase its pressure ratio at altitude. The only way a supercharger can do that is either with a pulley change or variable drive system.

Of course, altitude isn't the only thing that can reduce compressor inlet pressure. A restrictive air intake, an air intake located in a low pressure zone, a restrictive mass air sensor, inadequate inlet ducting, clogged air filter or excessive intake air turbulance and heating (i.e. placing your air inlet behind the radiator) are common mistakes that reduce compressor inlet pressure in the real world.

Kenne Bell makes the following suggestion to its supercharger customers:

"If you don't have access to a [flow] bench, install a tap behind each component in the inlet track, make a dyno pull or a WOT run on the street in low or second gear and read the vacuum gauge. If it's "0" there are no losses and, therefore, upgrading [pre-compressor]components will not help. However, if there is a 4" Hg reading - that's 2 psi of lost atmospheric boost . . . ."

Although Kenne Bell's suggestion does not take into account potential pre-compressor intake air pressure increases through vehicle velocity (ram air), the basic test method is reasonable for any form of supercharger or turbo.

KEEP COMPRESSOR OPERATIONS OUT OF THE "CHOKE ZONE"

noreply@blogger.com (Editor) — Sat, 23 Apr 2011 12:45:00 +0000

By 460-BBF-Turbo-In-CC (adapted from the legendary Car Craft Forum turbo blog)

"Don't choke now!" -- Grady Seasons (Keith McCready), "The Color of Money" (1986)

The following excerpt appeared on the forum at Bangshift.com:

"[The January 2011 issue of Auto Enthusiast magazing at pg. 30]has a story about a class project at WyoTech's Blairsville, PA campus. They built a crate 350 SBC with a single [Holset]HX35. It maxed out at a paltry 575 h.p. on 15 psi manifold pressure (charge cooled). This shows that the engine was obviously running well into the choke zone of the HX35. [Jay K.] Miller's map [Turbo: Real World High-Performance Turbocharger Systems ]shows that the HX35 goes into choke at ~ 50 lbs/min at 2.0:1 pressure ratio."

Sadly, Holset is tight-fisted with its compressor maps and there isn't a good on-line map of the HX35 available today.

Referring back to the old T66 map, every point to the right of the mapped area is in the choke zone of the compressor. Choke means just as it sounds -- the turbo compressor is choking the engine because it is not large enough to flow air efficiently in the quantities the engine COULD be consuming.

A turbo operating in the choke zone is too small for the engine at high r.p.m. It's that simple.

That doesn't necessarily mean that the turbo is too small at every r.p.m. For example, the WyoTech Blairville SBC reportedly has excellent low r.p.m. response, with a boost threshold (on-set of measureable manifold pressure increase) of ~ 2,000 r.p.m.

In another famous example (reported in the June 2001 issue of Hot Rod Magazine), Chris Stewart used a pair of junkyard 1986 Ford Thunderbird Turbo Coupe Garrett T03E turbos on a 472 CID BBF. The boost threshold was a mere 1,700 r.p.m. and it pounded out 714 lbs./ft of torque at the rear wheels through a power-guzzling non-lockup C6 automatic. And Stewart achieved this on a mere 10 psi of "boost."

The torque peak was a diesel-like 2,200 r.p.m.

However, the smallish turbos greatly restricted power at high r.p.m., limiting the 8.2:1 BBF to a weak 355 RWHP at a tractor-like 4,200 r.p.m.

Even though a turbo will still flow some air in the choke zone, the mass air density will be lowered by excessive charge heating. The turbo could also be at risk of overspeeding. And if the turbine (exhaust side) is fairly well matched with the compressor (as expected with factory turbos but not always true with aftermarket "hybrid" turbos) the turbine is likely also in an inefficent range of operation when the compressor is in the choke zone. Excessive backpressure and exhaust heat from a turbine opertaing in choke can hurt power production and exhaust valve longevity. In short, operating in the choke zone is akin to a dog chasing its own tail.

It should be clear by now, a properly fitted turbo or turbos must avoid the extremes of surge and choke. The "sweet spot" for turbo compressor operation is in the middle portions of the map where compressor efficiency is the highest.

What does "choke" mean? And why does it matter?

READING TURBO COMPRESSOR MAPS, PART III

noreply@blogger.com (Editor) — Sat, 23 Apr 2011 12:31:00 +0000

By 460-BBF-Turbo-In-CC (adapted from the legendary Car Craft forum turbo blog)

"One must strike the right balance between speed and quality."-- The Right Honourable Clare Short (Former MP,Birmingham Ladywood, UK)

The next compressor map elements of note are the series of r.p.m speed lines arcing from the surge limit line on the left over to the right.

Each of these speed lines is a graph of compressor performance at specific compressor r.p.m.

Warner (Street Turbocharging) and Hartman (Turbocharging Performance Handbook) both provide detailed explanations of how turbocharger engineers use these speed lines in building a compressor map.

The short version is that the turbos are run up to a particular test r.p.m. on a "test rig" (sort of a turbo dynomometer) and then the outlet flow is restricted with a valve to measure how efficient the compressors are at various mass air flow levels (the bottom axis of the map).

Note that until the compressor becomes a flow restriction (the right side of the map) that pressure ratio and compressor speed are closely linked. The speed lines turn down sharply at the right side of the map because the compressor is simply too small to efficiently supply any more mass air, reducing the pressure ratio.

On this map, the downturn in the speed lines becomes more severe at higher compressor r.p.m. levels. This suggests that increases in mass air flow beyond the efficiency range of the compressor can lead to drastic increases in speed as the compressor struggles to "keep up" with air demands.

The map speed lines also show that for each level of mass air flow, there are many pressure ratios that can supply enough air. Thus, if the pressure ratio increases, and mass air flow does not, then the output is being more restricted. (it works the same way with a garden hose nozzle)

Of course, in the real world, the "restriction" of compressor output isn't a test valve. It's the physical ability of the engine to induct, react, and exhaust air. That means better "breathing" engines require less pressure and compressor speed to obtain a particular level of mass air flow.

READING TURBO COMPRESSOR MAPS, PART II

noreply@blogger.com (Editor) — Sat, 23 Apr 2011 12:23:00 +0000

By 460-BBF-Turbo-In-CC (adapted from the legendary Car Craft turbo blog)

Turbo Tip of the Day: "Let it eat" -- Dean Skuza (Former AA/FC racer)

Moving from left to right on our old T66 turbo map, we see the dotted line labled "Surge Limit."

Pressures to the left of the surge limit are not mapped. Why? Because they are both unstable and potentially destructive to the compressor.

Surge amounts to air backing up inside the compressor and fighting to get back out through the entrance (or more properly, the "inducer bore")

To understand surge, imagine air being agitated into a mini-tornado by the compressor impeller (that's the fan blade/meat grinder thing that rotates).

Impeller

When flow out of the turbo is shut off or excessively restricted, the mini-tornado is not properly diffused into steady pressure because it has no place to go. So air being air, it takes the path of least resistance toward a lower pressure -- backing "out through the in door."

These reversals of flow fight the impeller's rotation. The exiting air molecules slam up against other air molecules that the impeller is attempting to induct (draw in). That causes inlet pressures to fluctuate and the impeller's blades to lose efficiency.

Thus, on the left side of the surge limit, the turbo compressor is not doing useful work because the exit flow is too restricted.

Simply put, surge occurs when the attempted pressure ratio is too high for the amount of air consumed by the engine. (Remember, just like with your garden hose or shop compressor, "boost" is not mass air flow. Boost without air flow creates surge)

Surge is most easily found (and heard) when a downstream throttle is slammed shut while the compressor is at speed. Surge sounds like chirping out of the compressor. Blow-off and recirculating valves are often used to combat this form of surge.

Using a turbo that is too large can also produce surge when the boost threshold is lower than an engine's abiliy to induct the compressed charge.

The simple rule is that for your turbo to live, you've got to "let it eat" by avoiding surge.

READING TURBO COMPRESSOR MAPS, PART I

noreply@blogger.com (Editor) — Sat, 23 Apr 2011 12:17:00 +0000

By 460-BBF-Turbo-In-CC (adapted from the legendary Car Craft turbo blog)

"Somewhere there is a map of how it can be done."

-- Ben Stein

Turbo manufacturers create compressor and turbine maps to summarize the air flow and density characteristics of turbochargers. Sadly, these maps are often withheld from grassroots Car Crafters (especially turbine maps).

But when you can find them, these maps are invaluable guides in turbo selection . . . if you know how to read them.

The next few [articles]are going to be about reading turbo maps.

To make these tips more relevant to our discussion of turbocharging a big-cube V8, here's a turbo compressor map for an old Garrett T66 (a pair of these would support well over 1,000 h.p.).

The first thing to notice is the left vertical axis of the map. Pressure ratio is simply the relationship between compressor discharge pressure to atmospheric pressure.

However, it is NOT a direct measure of how dense the compressed charge is because of charge heating during compression and atmospheric conditions outside of the turbo. (If it were, we wouldn't need the map!)

1.00 is basically no compression (compressor discharge pressure = ambient (outside) pressure)

2.00 means the discharge pressure is twice as much as ambient pressure.

3.00 means the discharge pressure is three times as much as ambient pressure.

A PROBLEM WITH JUNKYARD TURBOS

noreply@blogger.com (Editor) — Wed, 09 Mar 2011 18:15:00 +0000

By 460-BBF-Turbo-In-CC (adapted from the legendary Car Craft turbo blog)

"Don't send a child to do a man's job!" -- old Southern proverb

Someday turbos such as the tiny units used on the current Ford EcoBoost V6 engines will become widely available at the junkyard. And like an earler generation lured by JY T2s, T3s and T28s, some budget Car Crafters will undoubtedly buy the current generation of small JY turbos to use on big V8s with hopes of of dirt-cheap boost.

Years ago, more than a few Car Crafters grabbed up another small turbo, the once-ubiquitous Garrett AiResearch T3, and slapped pairs of them on all sorts of V8s, including Ford's 460.

Did it work?

It depends on what you wanted. If the goal is maximum pump gas power, the answer was no. Here's why:

Here's a turbo compressor map for one of the larger T3 variants. Note that the bottom axis is in lbs/min. of mass air flow. The highest flow mapped is ~ 35 lbs/min. Although the turbo doesn't stop flowing beyond that, the efficiency level becomes unacceptable (excessive air heating, potential overspeeding, and choking of the engine)

Recalling the general rule of thumb that one pound of mass air flow will support 9-10 horsepower, it should be abundantly clear -- even if you've got no idea how to read a turbo compresor map -- that a pair of these smallish turbos would be hard pressed to feed a 460 above 4,500 r.p.m. (If it's not, then stay tuned!)

Two of these turbos working together would struggle to supply enough "boost" at any pressure ratio for 630-700 h.p. And that's exactly what the Car Crafters who have tried to use pairs of JY T3s on 460s discovered.(See e.g. Trevor Cornwell's twin-turbo 460 Ford Fairmont)

And even that level would be adversely affected by excessive charge heating due to compressor inefficiency. Best efficiency would be at around a mere 200 to 225 h.p. per turbo -- a level that an "all motor" 460 should be able to easily achive on its own.

CONVERTING CFM TO MASS AIR, PART II

noreply@blogger.com (Editor) — Tue, 08 Mar 2011 19:37:00 +0000

By 460-BBF-Turbo-In-CC (From the legendary Car Craft big-cube turbo thread)

STP isn't very "real world."

Standard temperature and Pressure (STP) provides a means to account for the fact that air density and air volume are not linked.

STP - commonly used in the Imperial and USA system of units - as air at 60 [degrees]F (520 [degrees]R) and 14.696 pounds per square inch absolute (psia) (15.6oC, 1 atm) See, Engineering Toolbox.

Of course, engines in the real world seldom if ever operate at STP. Underhood temperatures, heat radiation, convection, and conduction, humidity and altitude variations help all assure that. That's one of the reasons why the SAE and others have developed more realistic standard references for automotive use.

Recall that we learned turbo manufacturers use 85 degrees F as "standard" (A. Graham Bell).

Is there really much difference between the various methods of converting CFM to lbs/min? Let's compare them:

Assume we're trying to convert 500 CFM to lbs/hr:

Warner method: divide 500 CFM by 13.7 = 36.49 lbs/hr

A. Graham Bell method: multiply 500 CFM by 0.07 = 35 lbs/hr

Miller method: multiply 500 CFM by 0.069 = 34.5 lbs/hr

STP method: multiply 500 CFM by 0.076 = 38 lbs/hr

Note that Jeff Hartman in Turbocharging Performance Handbook (2007) also uses the STP method.

Although the spread among the various methods is not that large, it appears that Miller and A. Graham Bell's conversion factors produce the most conservative results. Moreover, because they track with turbocharger industry standard practice, we'll use the 0.07 conversion factor.

But don't forget that these all of these factors are based on picking a somewhat arbitrary air temperature and pressure as a measuring point. Actual results may vary.

CONVERTING CFM TO MASS AIR (PART I)

noreply@blogger.com (Editor) — Tue, 01 Mar 2011 19:10:00 +0000

By 460-BBF-Turbo-In-CC (From the legendary Car Craft big-cube turbo thread)

"Sometimes things aren't as simple as they first seem."

The problem with converting CFM to lbs/min. is that the density of air varies with changes in altitude, temperature and even moisture content.

That's causes some to just ignore the whole thing. For example, Corky Bell (Maximum Boost) avoids the whole thing during turbo selection by using the "semi-incorrect term 'CFM.'" (Pg. 27).

Mark Warner suggests that to convert CFM to lbs/min, you should divide CFM by 13.7, but points out that the conversion assumes 85 degree (F) inlet temps. (Street Turbocharging, pg. 35)

A. Graham Bell in Forced Induction Performance Tuning (2002) explains that "Most compressor maps are corrected for 85 [degrees] F/28.4 in Hg or 20 [degrees] C/98 lmB air conditions; so to convert from CFM to lbs/min, multiply by 0.07." (pg. 90)

Jay Miller concurs, stating that multiplying CFM by .069 at "standard density" yields lbs/min. (Turbo: Real World High-Performance Turbocharger Systems, pg. 40)

But other sources claim that you should multiply CFM by .076 at Standard Temperature and Pressure. (STP)

Next: What is STP and which conversion method is best?

ADVANTAGES OF TURBOCHARGING

noreply@blogger.com (Editor) — Wed, 23 Feb 2011 17:37:00 +0000

By 460-BBF-Turbo-In-CC

Car Crafters often ask why turbocharge instead of building a bigger engine or using nitrous oxide as a "power adder."

Here are some of the advantages of using a turbo over "all motor"

1. "Area under the curve"-- A proper turbo engine can have a huge advantage in midrange and top end torque compared to a naturally aspirated engine.

For example, Here's the torque curve for a Dodge Viper 8.4 liter engine:

RPM Torque
3600 500 lbs/ft
4000 530
4400 545
4800 560
5200 560
5600 550
6000 525

Here's a torque curve for a turbocharged 4.6 liter Ford tested by Richard Holdener at 14 psi:

RPM Torque
3600 490 lbs/ft
4000 615
4400 720
4800 730
5200 755
5600 740
6000 705
6500 670

Here's the torque curve for a Gale Banks turbocharged 6.0 liter SBC on 91 octane at 8-12 psi:

RPM Torque
3800 590 lbs/ft
4400 605
4800 650
5200 650
5600 675
6000 650
6500 625

2. Fuel economy -- a smaller turbo engine with the same peak power as a radical big block is obviously a smaller engine when its off-boost. In cruise conditions, the turbo mill can yield 3-5 m.p.g. better fuel economy, or even better.

At $3.00+ per gallon, that can add up fast on a daily driver. For example, let's say you wanted to run the Hot Rod Power Tour at a round trip of 2,500 miles. With a 11 m.p.g. big block, it would cost $682 at $3.00/gallon. But with an 18 m.p.g. turbo engine, it would only cost $417. And a 22 m.p.g. turbo mill would run the trip for a paltry $340.

3. Drivability -- a 750 lbs/ft "all motor" engine is going to require a fairly big cam, carb and head combo. That usually means a rough idle and fairly crude low-speed manners. A loose torque converter and steep gears are generally necessary to keep the engine in its narrow powerband.

A 750 lbs/ft turbo engine can run a mild cam with a near-stock idle. Off-boost it can be so docile that you could let your grandma drive it. Turbos tend to work well with tighter torque converters and highway gearing.

4. Greater use of stock parts -- big "all motor" power typically requires high r.p.m. That means thousands for valvetrain and induction parts that can stand the revs. The lifespan of these parts is often much less in street driving than stock components.

The same power from a turbo mill can be achieved with mostly stock valvetrain parts. Reliability is measureably increased. Moreover, because high r.p.m, isn't necessary, the rest of the engine can use more stock parts.

For example, the April 2011 issue of Hot Rod magazine features the turbo build of a 150,000 mile GMC Denali engine (5.3-liter 5.3 LM7 engine). With nothing more than a mild LS6 camshaft (203.8/ 212.1 duration; .523/.522 lift; 115.9-degree Lobe Separation Angle) and a cheap Chinese turbo, the engine reportedly produced a massive 594 horsepower and 585 lbs/ft of torque.

5. Power density -- A turbo engine can be smaller and lighter than a big block of similar peak output. That can mean better weight distribution and more power-per-pound of engine.

6. A turbo engine can actually be cheaper to build -- Unless you're building a stock-based combo, building a big block can be expensive nowadays. It's not uncommon for an 800+ h.p. "all motor" big block to cost in excess of $15,000. The same level of power with a turbo engine often costs a fraction of that.

Now for nitrous

7. More tractable than nitrous oxide -- Most nitrous systems are on/off. A sudden 100-300 h.p. can be hard to manage. Even an expensive multi-stage nitrous system can have harsh transitions. Turbo engines can be more tractable because they can be modulated with the accelerator and boost controllers.

8. No bottle to run out-- A nitrous rule of thumb is 1 lb for 10 seconds = 100 h.p. A "200 shot" burns through 15 lbs of N20 in about 75 seconds. That can get expensive in a hurry.

75 seconds of turbo power doesn't really cost anything more than the fuel burned. And the turbo is still there for another 75 seconds . . . and another . . . and another . . . .

9. No nitrous backfires or other accidents -- Many heavy squeezers have stories to tell about intake manifold explosions, fireballs, clogged jets, melted pistons and other horrors of living on the edge with spray. A dialed-in turbo system simply doesn't have the same level of "drama." Many serious turbo racers report much longer engine service intervals than with N20.

10. Nitrous on the street is illegal in 38 states. And nitrous is banned in many forms of competition (drag racing is one of the few places where N20 is legal). There are a lot more places where you can run a turbo.

11. Less "prep" before a pass is needed with a turbo -- Turbos require no "purging" and no bottle heating. They're always ready for immediate action.

12. Easier to adjust for track conditions -- Dialing back a nitrous system for a "loose" track can be time-consuming (especually if it's a staged system). Dialing back a turbo system usually only takes a couple of seconds.

13. You can still have fun without race gas in the tank -- A big-power nitrous 'plant will require race gas to keep detonation at bay. On pump gas you've either got to change the jets or keep off the bottle.

But you can still make decent power with most turbo systems even when there's no race gas in the tank.

FIRST PRINCIPLES: AIR VOLUME IS RELATIVE

noreply@blogger.com (Editor) — Tue, 22 Feb 2011 14:27:00 +0000

By 460-BBF-Turbo-In-CC (From the legendary Car Craft Turbo Thread)

Most Car Crafters are more familiar with CFM [Cubic Feet Per Minute) than they are with measuring air in pounds/minute. After all, the time-honored measure for engine size is cubic inch displacement. And a cubic foot of air is 12 x 12 x 12 = 1,728 cubic inches. That's easy to understand.

Many of us have also read that it takes roughly 1.67 CFM for every horsepower on gasoline and ~ 1.47 CFM per pony on alcohol fuel. And some flow bench companies publish CFM charts such as this:

Flow**      Horsepower potential (V8 engine)

100 CFM   205.7 h.p.
150 CFM   308.6 h.p.

200 CFM   414.4 h.p.

250 CFM   514.3 h.p.

300 CFM   617.1 h.p.

350 CFM   720.0 h.p.

400 CFM   822.8 h.p.

450 CFM   925.7 h.p.

500 CFM   1028.6 h.p.

**cylinder head port measured at 28"

So why do we even need to think about air in lbs/min?

Because volume of air is relative. For example, a cubic foot of air at sea level has a lot more mass than a cubic foot of air in Denver, Colorado. And a cubic foot of air at 30" hg has more mass than a cubic foot of air at 14" hg.

NEXT: Converting volume to mass.

HOW MANY POUNDS OF AIR DOES IT TAKE TO MAKE ONE HORSEPOWER?

noreply@blogger.com (Editor) — Thu, 17 Feb 2011 14:53:00 +0000

By 460-BBF-Turbo-In-CC (From the legendary Car Craft turbo blog)

“He lives most life whoever breathes most air.” – Elizabeth Barrett Browning

The concept is simple: your engine has to take in enough air in order to burn enough fuel to reach your horsepower goal. But for many Car Crafters, the “experts” all seem to be speaking different languages.

At times, it all sounds like an alphabet soup. The tuning experts talk of “AFR” (air/fuel ratio). Then the carburetor and cylinder head guys talk of “CFM” (cubic feet per minute). Yet most of us measure fuel in gallons or liters, not CFM. And the CFM recommendations seem wildly inconsistent. (i.e. “You’ll need a 650 CFM carb and some 200 cfm heads . . . .”) Making it worse, the supercharger and turbo folks talk about “pounds of boost” or other arcane measurements.

Many Car Crafters just throw up their hands and copy what the next guy is doing. And sadly, too many never really understand why what they’re copying works or doesn’t work.

Turbo Car Crafters, however, don’t usually have anyone to copy. So to be successful, we’ve got to understand how to compare and measure air and fuel.

We’ll start with some of “rules of thumb” of power production. They’re not a substitute for working a PLAN in detail, but they’ll get us “in the ballpark” and hopefully give us a basis to understand what the “experts” are talking about.

According to the turbocharger engineers at Garrett, it takes one pound of air per minute to make nine horsepower (See, Julian Edgar, 21st Century Performance, at pg. 161).

Turbo expert Jay K. Miller (Turbo: Real World High-Performance Turbocharger Systems) makes the estimates a little simpler by suggesting that it takes one pound of air mass for every ten horsepower. (Miller at pg. 40).

Engineer Mark Warner also uses the easier 1:10 rule of thumb, stating that once you know the mass flow rate into an engine, you can multiply it by 10 to get a horsepower estimate. (Warner, Street Turbocharging at pg. 29)

Others suggest that at the torque peak, each pound of air will support about 9.5 h.p. and at the horsepower peak each pound of air supports about 10.5 h.p. The popular 1:10 “rule” seems to split the difference.

In actual practice, each of these “rules of thumb” will be varied by many factors. But the basic concept of combining a “mass” of air with a smaller “mass” of fuel remains fundamental.

PLAN FOR TOP SPEED

noreply@blogger.com (Editor) — Mon, 14 Feb 2011 18:08:00 +0000

By 460-BBF-Turbo-In-CC (from the legendary Car Craft turbo thread)**

"Above 50 m.p.h., air is your biggest opponent."

A few Car Crafters don't "live their lives a quarter-mile at a time."

Their speed dreams are just getting started at the end of the 1320. Bonneville, Maxton, and the Texas Mile are places that matter to them. The calculations and assumptions for a street/strip vehicle aren't enough for top-enders. Developing a PLAN for pure top-end speed in a street car is a little more involved.

As anyone who has ever stuck their arm out the window at speed can testify, air becomes a powerful force once velocity increases. Air, in fact, becomes the main resistance to top speed.

Making this an even harder challenge is the "dirty" aerodynamics of our favorite "muscle cars." With a few exceptions, Detroit paid little attention to aerodynamic efficiency before the end of the 1970s. So some of our project cars have coefficients of drag (Cd) of .45 or worse.

Aerodynamics can be a complicated, math-intensive subject. Serious analysis typically requires expensive wind tunnels and computational fluid dynamics software. That's not grassroots Car Crafter stuff.

But back in 1984, the Chevrolet Power Service Manual (5th ed.) attempted to "dumb it down" for Car Crafters building full-bodied muscle cars. Using Chevy's modestly complex set of formulas (reportedly derived from GM wind tunnel research), we can estimate the power required to punch a boxy muscle car through the air at more than 200 m.p.h. If we assume a "dirty" .5 Cd and a frontal area of 24 square feet, 232 m.p.h. would require a masssive 1203 horsepower! Knocking back the target velocity to 200 m.p.h. still requires in excess of 800 h.p.

Of course as generations of "land speed" racers will tell you, using a smaller, more aerodynamic body can dramatically reduce the power requirements. But if you're interested in pushing a blocky, stock-appearing muscle car over 200, you're going to need to PLAN for some serious, sustained horsepower.

**Reposted with permission of the author.

APPLICATION OF POWER-TO-WEIGHT THEORY

noreply@blogger.com (Editor) — Fri, 11 Feb 2011 19:11:00 +0000

By 460-BBF-Turbo-In-CC (from the legendary Car Craft turbo thread**)

"If you don't know where you're going, you'll probably end up somewhere else."

Let's say our project car is a typical V8 compact or intermediate that weighs ~3,200 lbs. Add in the following:

120 lbs. for a tank of fuel (Gasoline 6.2 lbs./gal.)
200 lbs. for extra safety equipment required by track rules
200 lbs. for "Driving ballast" (you)
50 lbs. for the various jetsam that accumulates in a real street car (tools, maps, lawn chairs, etc.) or maybe some actual ballast to improve weight distribution.

Now the car's tipping the scales at nearly 3,800 lbs. Now let's say that you've figured out that to humiliate some arrogant jerk in a Viper ACR or a Corvette ZR1 that you need at least 140 m.p.h. in the quarter mile to be safe.

Recall that 140 m.p.h. requires a minimum of one horsepower for every 4.67 lbs. So 3,800 divided by 4.67 = 814 h.p. Factor in an extra 15% "reserve" and the horsepower target is 936 h.p. Note that this assumes that the car goes through the timing traps at the horsepower peak. If it doesn't, you'll need a higher peak to make sure that the car is making the minimum required power at the point on the torque curve that the car's gearing causes it to reach the timing traps.

If we up the target to 150 m.p.h. (3.79 lbs per pony), then we need a minimum of 1003 h.p. Add in the 15% "fudge factor" and the PLAN target is 1153 h.p. It should be clear now that quarter mile speeds over 120 m.p.h. in a typical heavy street machine are going to require in excess of 500 h.p.

And the power requirement escalates dramatically as speeds inch upward (i.e. raising the trap target from 140 to 150 requires around 200 more h.p. in our example).

FIRST PRINCIPLES: FORCE EQUALS MASS TIMES ACCELERATION

noreply@blogger.com (Editor) — Fri, 11 Feb 2011 19:01:00 +0000

By 460-BBF-Turbo-In-CC (from the legendary Car Craft turbo thread**)

"Force Equals Mass Times Acceleration (F=MxA)"

The first step in developing a PLAN for where you want to end up is determining how much power you're going to need to get there. For most Car Crafters, the "holy grail" of high-performance is power-to-weight ratio. It's the most fundamental relationship.

And for an overwhelming number of Car Crafters. power-to-weight is best benchmarked by standing-start acceleration over a quarter mile. Decades ago, Chrysler engineers worked out the math for how much power it takes to hit a target trap speed in a production-based vehicle at the end of a quarter mile.

Based on their formula:

M.P.H. Lbs Per Horsepower
100 m.p.h 12.82 lbs/hp
110 m.p.h 9.61 lbs/hp
120 m.p.h. 7.40 lbs/hp
130 m.p.h. 5.38 lbs/hp
140 m.p.h. 4.67 lbs/hp
150 m.p.h. 3.79 lbs/hp

Now to avoid disappointment and account for differences in measuring horsepower, mechanical efficiencies, and other factors, I'd add in 10-15 percent more horsepower, just to be safe.

Notice that these results don't mention engine size or overall weight. A big, heavy car with ~ 5 lbs/h.p. should have roughly the same trap speed as a small, light car with ~ 5 lbs/h.p. (excluding aerodynamic effects). It just takes more "engine" (and budget) to make a heavy car as fast as a light one.

The results don't mention [elapsed time] (E.T.) because "quickness" tends to be influenced by more factors than effective h.p. More often than not, E.T. is a measure of how effective a car is at relatively low speeds in the first third of the quarter mile. But unless you're doing something really wrong (i.e. running FWD, horrible weight distribution, "no traction" tires, "peg-leg" differential . . . .) you should be able to obtain at least the following under proper conditions on the street:

Lbs/Hp E.T. Zone

12.82 14s

9.61 13s

7.40 12s

5.38 11s

4.67 10s

Obviously, a well-sorted drag-oriented supsension and better tires will produce quicker E.T.s, but for conservative PLAN purposes, these numbers will get you "in the ballpark" on how much power to build for.

**Reposted with permission of the author.

LIMITATIONS ON HOME-BUILT TURBO PROJECTS, PART III

noreply@blogger.com (Editor) — Fri, 11 Feb 2011 18:56:00 +0000

“Genius has limitations, stupidity is boundless” – Anonymous
By 460-BBF-Turbo-In-CC (from the legendary Car Craft turbo thread**)
LIMITATIONS (Part 3)

7. “The Man” – Car Crafters in many states have to watch out for the long-arm of the law. In fact, CC’s failure to do a big-cube turbo project is probably in part because CARB hates retrofit turbocharging. And even in the states where there’s still a little liberty left, Car Crafters face restrictions on noise, how much engine can be hanging out, and other legal limits.

8. Sanctioning body rules – If you’re going to run in any organized competition, then sanctioning body rules are going to be a limitation. For turbo Car Crafters, it may mean limiting the number of “power adders” and adding extra safety equipment. It probably will require adherence to specifications on fuel, fuel additives, cooling strategies, wiring, and plumbing.

9. Reliability and maintenance – This one is the fusion of time, money, parts quality, and practicality. At least until recently, Austin Coil could rebuild John Force’s AA/FC after every quarter mile pass. But most turbo Car Crafters expect their creations to last for thousands, if not hundreds of thousands of miles. And while some elevated maintenance may be tolerable, constant fussing and repairs get old fast. So the PLAN for a realistic street/strip turbo car has to take into account reliability and reasonable service intervals.

If you don’t know your limitations going in – or ignore them – then the outcomes of your turbo build will be waste and frustration, if not expensive disaster.

**Reposted with permission of the author.

LIMITATIONS ON HOME-BUILT TURBO PROJECTS, PART II

noreply@blogger.com (Editor) — Fri, 11 Feb 2011 18:45:00 +0000

By 460-BBF-Turbo-In-CC (from the legendary Car Craft turbo thread**)

"The man with insight enough to admit his limitations comes nearest to perfection.” – Goethe

4. Fuel quality – The trickest engine in the World is useless if you can’t obtain or afford its fuel. The most obvious limit on the amount of power you can jam out of a street/strip engine is going to be fuel quality. A few lucky Car Crafters have access to E85. An even smaller number will put up with the hassle of using racing fuel. But everywhere else, practical street/strip cars have to burn weak pump gasoline most of the time.

5. Parts quality – It does little good to PLAN a 1000 h.p. turbo engine if you’re using a production block and reciprocating assembly that self-destructs at ~ 600 h.p. So we’ve got to be realistic about how much abuse we can expect the parts we’re forced to work with will absorb.

6. Loyalty and style – Most turbo Car Crafters are going to build a make and model of car that appeals to them for reasons other than pure objective performance. That usually means the turbo project car is going to be heavier, less aerodynamic, and less weight-balanced than optimum.

And our powerplant choices are also often made based on personal history, brand loyalty, or whatever we’ve already got. They’re not usually based on what is the best engine design available to meet our chosen performance parameters. But a great thing about turbocharging is that it can be a huge equalizer for those committed to “obsolete” engine designs.

Moreover, many of the choices we make in crafting a project car are for reasons other than hitting a performance target. As David Freiburger once observed, this sport involves a big fashion component. It also nurtures some fairly strong traditions and peer pressure. Thus, one of our limits will be our self-imposed sense of what looks and feels “right” without regard to objective performance.

The GN/Type-T Regal is a perfect example of a turbo project car that is often picked for reasons other than optimum performance potential. Objectively, they're boxy. They're relatively heavy. They have poor weight distribution. They're saddled with an obsolete two-bolt main six and a cast crank. The cylinder heads are fairly restrictive. The factory turbo system was hardly optimized. And in stock form, they're down about 80 h.p. or more to many modern DOHC V6s.

So from a purely objective assessment of performance potential, there are plenty of better choices for a turbo project car. But over the past 25 years, Turbo Buick Car Crafters have often built these cars to be brutally fast and quick! And we're all glad that they have! The point here is that if you're carrying a torch for something that's off-beat or that has less than optimal hop-up potential, you should be honest about it going in and adjust your PLAN, budget, and performance goals accordingly.

**Reposted with permission of the author.

noreply@blogger.com (Editor) — Thu, 10 Feb 2011 15:08:00 +0000

LIMITATIONS TO BIG-CUBE HOMEBUILT TURBO PROJECTS, PART I

BY 460-BBF-Turbo-In-CC (from the legendary Car Craft Big-Cube Turbo Thread)

A man’s got to know his limitations.” – Harry Callahan, “Magnum Force” (1973).

The Jetfire V8 and recent Indy V8s can only provide limited guideposts for Car Crafters on turbocharging.

The comparison of these engines does show that success in turbocharging (huge torque & massive horsepower) depends on more than just sticking on any old turbo laying around.

But neither the Jetfire nor the Indy V8 would be good street/strip mills. Back in the early ‘60s, Oldsmobile dealers were often busy replacing blown head gaskets or removing Jetfire turbo systems and replacing them with four-barrel carbs. Bore corrosion was epidemic. So the Jetfire stands as a cautionary tale of what not to do.

And an Indy V8 on the street would produce horrible fuel mileage and unsatisfactory power below 5,000 r.p.m., even if you could afford the huge “buy-in,” packaging, and servicing costs. So Indy engines merely suggest general areas for improvement of street/strip turbo powerplants.

Thus, a practical PLAN for turbocharging a OEM production street/strip engine means building within the walls of a vastly different “box” of needs and performance expectations.

But before we identify our performance parameters and goals, we’ve got to take stock of the outer limits. We’ve got to know our limitations.

These limitations should be regularly consulted as we PLAN and build. They are a “reality check” on our turbocharged enthusiasm and creativity.

LIMITATIONS (Part 1):

1. Money – The big limit is always going to be money. While it’s not the same sum for every Car Crafter, everyone has a maximum budget. The only way a home turbo project becomes feasible for most Car Crafters is by avoiding the expense of custom-built parts and costly “experts” whenever possible. Thus, turbo Car Crafters are mostly stuck with mass-produced OEM and aftermarket parts and self-help labor. What is cheap and readily available often trumps what would be best.

2. Time – A close cousin to money is time. Most street/strip turbo Car Crafters are not engineers. Most are not professional fabricators. Most cannot spend every waking hour ironing out build problems or contemplating turbo tuning theory. So something that’s quick, relatively simple, and easy-to-build is almost always better than something so time-consumingly “perfect” that’s never completed.

3. Practicality – If it’s not practical, we won’t drive it very much. It’s that simple. A street/strip machine that guzzles race gas, or idles at 1500 r.p.m., or won’t start when it’s cold, or has to stop for refueling every 75 miles, or takes three hands and three feet to operate, or hides small children behind its giant hood scoop won’t stay attractive for long in the “real world, ” regardless of how “wicked” and “gnarly” it is in our imagination.

noreply@blogger.com (Editor) — Thu, 10 Feb 2011 15:01:00 +0000

PLAN back from where you want to end up.

BY 460-BBF-Turbo-In-CC (from the legendary Car Craft Big-Cube Turbo Thread)

To some Car Crafters it's self-evident why turbocharged Indy V8s "processed" more than four times more air mass than the 1960s Oldsmobile Jetfire V8. Others may just throw up their hands and mutter something about "racing engine" and "unobtainium."

But we can learn important things about planning PLAN from the Indy V8s.

While the Indy V8 engineers may have had huge budgets and the liberty to design purpose-parts (something most Car Crafters will never have), they were forced to design in a fairly restrictive rules box.

THE GOOD: The "N Factor" (number of combustion events per minute) of PLAN was rules-limited to eight cylinders and 12,000 r.p.m (although development had once taken r.p.m. levels as high as 15,000). That's 48,000 cylinder firings per minute at redline. That sounds like a lot until you realize the cubic-inch displacement factors (L & A) were limited to 2,650 cubic centimetres (161.7 cu in; 2.65 liters) That means each cylinder was only a little over 20 cubic inches.

The engines needed to last only 700 miles or less between major rebuilds. The designers were free to use many premium materials, dual overhead camshafts, multiple valves per cylinder, multi-point fuel injection and other strategies to optimize high r.p.m. power.

Fuel was detonation resistant methanol. Thus Factors A (area) and L (stroke length) were not as dependant on avoiding detonation (more on this later). And relatively high compression could be employed to extract more work from the "working fluid" (fuel + air).

THE BAD: The Indy V8s were limited to one turbocharger and very low intake manifold pressure. They could not use charge cooling (although it was hardly necessary considering the cooling effect of alcohol fuel and the low "boost" levels).

They needed to be responsive over a moderately wide r.p.m. range. They also needed to be a structural member of the chassis. But weight and packaging were restricted by chassis aerodynamics and handling considerations.

Fuel consumption and on-board capacity were both limited (limiting the amount of fuel enrichment for in-cylinder cooling). The engines needed to produce enough power to overcome extremely high-drag bodies at speeds of more than 230 m.p.h. and to accelerate 1500-1600 lbs from 35-150 m.p.h. harder than most doorslammers several times per lap on road courses.

So how did they make it work?

Mostly by concentrating on maximizing Factors P & N within the limits of the rules.

Optimizing Factor P (cylinder pressure) on low "boost" required all of the standard "all motor" hop-up techniques: Generous breathing, optimized by oversized bores (Factor A), large valve curtain area (the total amount of valve opening), large straight ports, pressure-wave tuned intakes manifolds and exhaust headers. They also increased efficiency through high compression and lowered crankcase backpressure by dry-sump scavenging (less air resistance to the power strokes from the back of the pistons).

The aerodynamics, bearings, and rotating assemblies of indy car turbochargers were also optimized for efficiency and improved responsiveness(more Factor P quicker, at lower r.p.m., and with less charge heating) Even the intake air bell was aerodynamically engineered to swirl the air into the turbocharger compressor to improve its efficiency.

To maximize Factor N, they built everything to withstand and enable sustained high r.p.m. They moved the torque peak closer to the rev limit. Stroke length (Factor L) was reduced to serve the needs of Factors N and P (bigger bores allow for more valve curtain area; shorter strokes reduce loading on the reciprocating assembly) They also helped get more of the work accomplished by Factors P & N through to the wheels by targeted reductions in rotating mass and reduced oil windage.

It should be clear that the success of the turbocharged Indy V8s didn't occur from just slapping a turbo on the engine and calling it good. The engineers instead focused on where they wanted to end up and the restrictions placed on getting there. Then they adjusted the PLAN factors to achieve their targeted results.

noreply@blogger.com (Editor) — Thu, 10 Feb 2011 14:55:00 +0000

Fail to PLAN, plan to fail.

BY 460-BBF-Turbo-In-CC (from the legendary Car Craft Big-Cube Turbo Thread)

Corky Bell's celebrated turbo book Maximum Boost: Designing, Testing, and Installing Turbocharger Systems introduces readers to the acronym PLAN to explain power production:

P -- Pressure (as in cylinder pressure)

L -- Length (as in stroke length)

A -- Area (as in bore area)

N -- Number (as in number of combustion events per minute)

Bell uses PLAN to show why turbocharging is more practical and cost-effective than most other forms of Car Crafting at boosting the output of production engines.

PLAN is also useful to explain yesterday's low boost comparison. The Indy V8's greater ability to consume air (and thereby extract power from fuel) is the result of optimizing PLAN within restrictive rules. The Jetfire's weak numbers are mostly from ignoring PLAN.

First, let's look at the Jetfire:

The Jetfire V8 used an early, less-efficient, smallish turbo compressor drawing through a restrictive gasoline carburetor. It forced the hot supercharged air-fuel mix into a constrictive cast iron intake through small ports regulated by a mild camshaft.

Although the Jetfire's static compression was in excess of 10:1 (which in many driving conditions jacked up peak cylinder pressure beyond the detonation threshold), it exhausted the waste gasses into simple log manifolds that joined together before a single scroll turbine section. The turbine exhausted into a small, restrictive exhaust and muffler system. Maximum effective RPM was less than 5,000.

In terms of PLAN, average cylinder pressure (Factor P) was held down by inefficient induction. It was artificially spiked by high compression, but that did not increase the amount of "working fluid" (air and fuel) available for combustion and ultimately led to less available power than an equivalent peak cylinder pressure produced by other means. Heat and kinetic energy use was not optimized.

The number of compbustion events per minute (Factor N) was also limited by induction design, cam timing, valve size, port size, short-block design, materials and exhaust design. (Pumping up Factor N is usually the most expensive way to increase power because it requires either adding more cylinders or increasing R.P.M.)

Thus, although the Jetfire has a small advantage in displacement (Factors A & L) over the turbo Indy V8, it is far outweighed by other factors limiting mass air flow.

As Bell points out at some length, Factors A & L are generally hard to change and require huge increases to yield big results. Spending $2,500+ on boring and stroking most engines will typically produce only a faction of the power of the same investment in a turbo system.

On the other hand, starting with a big-cube V8 can reduce the need to hike the P and N factors to budget-crushing levels to obtain tire-melting power!

noreply@blogger.com (Editor) — Sat, 05 Feb 2011 00:55:00 +0000

WHAT IS "BOOST"

BY 460-BBF-Turbo-In-CC (from the legendary Car Craft Big-Cube Turbo Thread)

"Boost" can be oversimplified as resistance to air flow. Every tire on your car probably has 30+ pounds per square inch of pressure, but (hopefully) no air flow. Your shop compressor often has more than 100 psi, but at air flow volumes that are minuscule to the demands of even a low-performance automobile engine.

When we read "boost" from a tap in the intake manifold of an engine, what we're mostly reading is resistance to air flow between the compressor impeller and the cylinders. Now that's not necessarily a bad thing. Resistance to flow between the compressor impeller and the compressor housing is part of how any centrifugal compressor increases air density.

But it should be apparent that a high "boost" level doesn't necessarily mean high mass air flow into the engine. 14 psi of non-chargecooled "boost" through a Stromberg 97 on an asthmatic flathead V8 isn't going to result in as much mass air flow as 14 psi of cooled "boost" through a modern EcoBoost V6.

In other words "boost" is relative.

A great example of this is comparing the ancient Oldsmobile Jetfire V8 to the last of the turbocharged Indy V8s. Both were non-charge cooled, single turbo engines. Both engines ran less than 6 psi of turbo "boost." The Indy V8 was rules-limited to a mere 161.7 cubic inch displacement. The Oldsmobile Jetfire displaced 215 cubic inches. Yet the mass of air consumed by a turbo Indy V8 was roughly four times more than the Jetfire Olds. And it was at a lower peak boost level to boot! (4.91 psi initially and reduced to 1.96 psi by the end of the Indy turbo V8 era).

So the lesson here is that turbo Car Crafters should be focusing mass air flow instead of "boost." "Boost" is good for bragging, but it's mass air flow that wins races.Forget the old saw "there's no substitute for cubic inches." The truth is that there's no substitute for mass air flow.**

(**Okay the nitrous oxide fans may carp at this last point, but N20 injection is merely substituting part of the ordinary air mass for a higher quality (more oxygen-rich) gas supplied under high pressure. So it is is in essence a form of increasing mass flow)

noreply@blogger.com (Editor) — Sat, 05 Feb 2011 00:45:00 +0000

PREPARE FOR THE RELAUNCH!
Hydra and Cammie are gone. And there's a "new sheriff in town . . . ."