Improviz

I was rifling through some old mags today, and came across the test of the Dinan S3 supercharged E46 M3. The car supposedly produced 462 crank horsepower, yet only trapped at 112 mph, which, at a curb weight of 3620 pounds after adding 180 pounds for driver to its 3440 curb weight, gives a calculated horsepower of 397.

This brought the calculator to mind. The theoretical horsepower a 333 hp motor should produce with 5 lbs of boost is 446, and with 6 lbs it is 469.

Hmm....and the Dinan car didn't only add the supercharger: they also had new throttle bodies and exhaust on that car.

So, I thought I'd investigate some other cars for which we know the stock crank hp and see how the calculator holds up:

Saleen s281: 6.5 psi boost.
Crank hp stock: 300
Theoretical horsepower : 422 @ 6psi, 455 @ 7 psi => ~430
Rated by tuner: 400
Trap speed: 110 mph
Calculated hp from trap: 401

Active Autowerks 330iA: 7.5 psi boost
Crank hp stock: 225
Theoretical horsepower : 342 @ 7psi, 354 @ 8psi => ~348
Rated by tuner: 310
Trap speed: 102 mph
Calculated hp from trap: 305

2001 Dinan ISR-3 M Roadster: 10 psi boost + intake and exhaust work
Crank hp stock: 240
Theoretical horsepower : 407 @ 10psi
Rated by tuner: 396
Trap speed: 106 mph
Calculated hp from trap: 305 (not a typo, same as for the 330--this is lighter)

Kenny Brown Marauder S: 7 psi
Crank hp stock: 302
Theoretical horsepower : 459 @ 7psi
Rated by tuner: 460
Trap speed: 108 mph
Calculated hp from trap: 444

Kleemann 55S8: 7.3psi boost
Crank hp stock: 362
Theoretical horsepower : 550 @ 7psi
Rated by tuner: 570
Trap speed: 117 mph
Calculated hp from trap: 501

RMS M5 Superfast: 11 psi
Crank hp stock: 394
Theoretical horsepower : 668 @ 10psi
Rated by tuner: 608
Trap speed: 114 mph
Calculated hp from trap: 468

So, it seems that the calculator can definitely get you in the ballpark, but it might not get you to home plate. It is definitely a mixed bag, especially at the higher boost levels where the cars with high stock compression (11:1 and up) clearly could not approach theoretical horsepower from the calculator, probably due to the engine computer having to severely retard timing to avoid detonation.

On the vehicles with the lower compression motors, the calculator's numbers were more accurate, so it's probably geared towards big ol' American V8s w/low compression, and won't do so well on higher-compression German 6s' (or ultra-high compression German 8's), particularly at higher boost levels.

Iow, I'd be more likely to believe its numbers for a 5.0L V8 running 9.5:1 compression than a 4.0L V8 running 12:1.

jpohl402

I've been wondering for quite some time now.....
What does FTW mean?

Improviz

Fort Worth, a city in Texas.

OK, seriously, in addition to that it is commonly used as an abbreviation for "For The Win".

jpohl402

^^^ ok thanks ^^^

BlownV8

The calculator uses RWHP and not crank HP so that might be the first false assumption in your calculations in determing the accuracy of the calculator. The HP calculator is very close but not dead on. It will give you a very good idea of what boost will do for your car given you know the starting RWHP, boost level, octane of fuel, and efficiency of the intercooler.

Improviz

Incorrect. The calculator allows for either crank or wheel hp; it is selectable. Look at the tab just to the right of where you enter the horsepower.

As to that being the "first" false assumption: care to take a crack at listing any more, given that my statement was neither false nor an assumption? You're the one who's assuming that this calculator is seemingly without flaws, and the data clearly show otherwise. Sometimes it is close, sometimes it is very far off.

Within an error of as much of 50% when compared to what it predicts vs what engines actually produce at the specified boost level.

Whoop-de-do.

No calculator is going to give you a high level of precision given as little information as that calculator requests. It does not even ask for displacement, for pete's sake, nor compression, etc....it's ridiculous to maintain that this thing is some kind of Oracle of Boost: it is a first order attempt at solving a multidimensional problem.

splinter

If only Improviz could substantiate his posts’ perspectives - with data - in an articulate manner...

BlownV8

You are right. I made the false assumption and I see that it is selectable. I only know from my first hand experience with RWHP and Dynojet usage that it was close. I don't have a tremendous amount of magazine knowledge so you will have to forgive me.

Improviz

Similarly, you'll have to forgive me, as I only have my knowledge of Engineering and the Laws of Physics to get me by, along with data that plainly show the calculator to be wrong.

But hey, I suppose that it's plausible to say that introducing a given psi into an engine, any engine, regardless of the displacement of the engine, compression ratio, fuel delivery system, cam, heads, exhaust system, type of supercharger (roots? twin screw? who cares??) will give the same horsepower boost. I mean, what else do you need to know, really?

It's all about the boost. There are no other factors that need to be taken into account. And the data clearly show this.

Oh, wait: the data doesn't clearly show this.

Darn.

BlownV8

Most of the ones you submitted as examples are very close:


Saleen s281: 6.5 psi boost.
Crank hp stock: 300
Theoretical horsepower : 422 @ 6psi, 455 @ 7 psi => ~430
Rated by tuner: 400
Trap speed: 110 mph
Calculated hp from trap: 401

+ 5% off tuner rating.



Active Autowerks 330iA: 7.5 psi boost
Crank hp stock: 225
Theoretical horsepower : 342 @ 7psi, 354 @ 8psi => ~348
Rated by tuner: 310
Trap speed: 102 mph
Calculated hp from trap: 305

+ 10% off tuner rating.


2001 Dinan ISR-3 M Roadster: 10 psi boost + intake and exhaust work
Crank hp stock: 240
Theoretical horsepower : 407 @ 10psi
Rated by tuner: 396
Trap speed: 106 mph
Calculated hp from trap: 305 (not a typo, same as for the 330--this is lighter)

+3% off tuner rating.


Kenny Brown Marauder S: 7 psi
Crank hp stock: 302
Theoretical horsepower : 459 @ 7psi
Rated by tuner: 460
Trap speed: 108 mph
Calculated hp from trap: 444

-1 hp off tuner rating.


Kleemann 55S8: 7.3psi boost
Crank hp stock: 362
Theoretical horsepower : 550 @ 7psi
Rated by tuner: 570
Trap speed: 117 mph
Calculated hp from trap: 501

- 3% off tuner rating.



RMS M5 Superfast: 11 psi
Crank hp stock: 394
Theoretical horsepower : 668 @ 10psi
Rated by tuner: 608
Trap speed: 114 mph
Calculated hp from trap: 468


+ 10% off tuner rating.


Given your examples, I'm surprised at how close the calculator is to the tuners HP ratings. There are so many different variables that come into play like the superchargers efficiency, intercooler type and design, fuel, timing, ETC, ETC,... The huge variances seem to come from engines with higher CR and it would appear that the tuners are reducing the timing to compensate for the boost. It's always a good idea to save the engine from preignition.

In the grand scheme of things, does it really matter to expel the kind of energy arguing the merits of a calculator that ESTIMATES HP? The calculator does give you a very good estimate of what the engine should make with boost given the input. Are you going to bet your house on the calculator - hell no. Is it good for a summary glance of what boost can do for your engine - yes.

I'm not defending Skratch 77 because I know he is a BMW troll nor am I arguing with you. I simply provided a link to a hp calculator that does a good job of letting you know what boost can do for an engine. That's it and nothing more.

Improviz

Not when you look at test results instead of tuner data.

?? % error is the error over the actual (estimated - actual)/actual. In this case it is (430-401)/401 = 7% error. Even doing it your way, the error is 30/400 = 7.5%.

Again, it is 43/305 = 15%.


Sorry, but this car was rated at 396 hp and trapped at a lower speed (by 2 mph I believe) than a 333 hp M Roadster would trap a year later. It may be rated at 396, but no way in hell is it putting out 396 hp and trapping at 106 in a 3100 pound car. Error is 102/305 = 33%.

This one is closer, showing the problem with the calculator: above, this same motor was 7% off both in tuner rating and in trap, yet here it's almost spot on. Clearly, there are other factors at work, which is what I said in my previous post.

And again, the tuner rating is a joke. The car trapped at 117, which stock 55k cars have hit weighing in 300 pounds heavier. Further, the C63 has hit 116 rated at 462. It is clearly overrated, and the error is 49/501 = 9.8%.

This one is the biggest joke of all, and either you're not reading these numbers carefully or you're purposefully ignoring them. If an E55 can trap at 116 with 500-ish, don't you think an M5 with 668 (or 608) horsepower could trap better than a best (and remember: they use their best results in C&D) of 114?? Btw, this one is an error on my part. Horsepower calculator actually comes back w/483 hp here. This gives error of 185 horsepower vs. theoretical, or 39.5%.

Again: the traps tell the tale, and some tuners are clearly a bit more realistic in their ratings than others.

Yes, which is what I pointed out when I first presented the data: I stated that it is clearly more accurate on low-compression motors.

You tell me. You're the one who's been defending the damn thing as though you personally wrote it. I'm just tired of getting needled by you for pointing out that it is a first order estimation of a nth order system, and is thus going to be inherently very error-prone and inaccurate under some circumstances, which it obviously is.

For a low compression V8, it seems to work very well. For high compression I6s and V8s, not so well. The authors point out that there are diminishing returns at higher boost levels due to detonation, but they should also point out that the same will hold true at higher compression ratios, for the same reason. A lower-compression motor allows you to introduce higher boost levels without detonation, which is why manufacturers (including Benz) always lower the compression of their FI cars' motors.

Could've fooled me. I'm merely observing that the thing is not panacea, and in every case you've overreacted and acted as though it is foolproof. It is not, because it cannot be with such a limited amount of data input.

For certain engines, it clearly works well, but for others, it clearly does not. That's my point.

Anyway, we'll see how this AA system works on the M3 when it comes out and we start seeing traps. If it's as strong as claimed, it'll be a lightning bolt provided the engines don't grenade...time will tell.

BlownV8

Holy crap! You can beat a dead dog to death. You have waaaaaaaay too much time on your hands. You are also using another estimator of HP - trap speed.

All the tuners are wrong. You are right - end of story.

Really, no really......I could give a rats *** about the calculator. I have no personal tie to it at all. It is a good estimate of hp given boost - that's it.

Trap speeds are a good ESTIMATE of HP to the wheels. Will it give you exactly what the car is making at the crank - no. You don't have any idea what the driveline is robbing. Hell, a heavy set of wheels will effect your trap speed. Elevation will effect your trap speeds. Multiple issues can effect your trap speed.

A. You don't know how much power the driveline is robbing.

B. You don't know the atmospheric conditions of the runs, altitude, ETC, ETC.

Determing crank HP from trap speed when you don't know all the variables may even be less accurate than the stupid calculator I linked. You are going to have issues with each method. The only way to truly determine crank HP is to remove the engine and hook it to an engine dyno - period. Everything else is an ESTIMATE and you can't tell with any definitive certanty what the crank hp of the car is by looking at trap speed.

If a 2003+ E55 does not run through the traps at 115 MPH, it does not have the HP Mercedes advertises or?

If you have any questions on my view of Skratch 77, you can check my posts. I reguarly call him out as a BMW troll and always have. The only time he has any input is to defend BMW's.

sticky2

Why exactly are looking at the Dinan supercharged M3? It is the weakest of all supercharged E46's. Look at VF sometime if you want to see impressive results, as in mid 11's in the 1/4 @ over 122 mph and 500 + wheel on the E46 M3.

sticky2

This is incorrect, what is with this typically pick up nonsense?

The M3 heads flow extremely well, part of the reason it picks up the numbers with boost that it does. The E46 M3 typically picks up 20 wheel per PSI of boost. The E92 M3 is closer to the 30 wheel hp per psi gain, you simply are not informed in regard to the M3 forced induction scene. The ESS car is completely stock except for the blower.

433 wheel hp for a supercharged E92 M3? LOL! That number is embarassing even for the E46 M3 supercharged.

Improviz

You might spend a bit of time researching the equation F=MA.

If a tuner says a 3100 pound car is producing 400 horsepower, and it traps at a max of 106 mph when the same car, at the same weight, with the same driveline, traps at 108 with a 333 horsepower motor, and when Corvettes with 400 horsepower weighing 200 pounds more trap at 114, then yes, I'd say it's a safe bet that the car isn't putting out anywhere NEAR 400 horsepower.

Horsepower and weight are excellent predictors of a vehicle's trap speed, and that equation I use has been curve-fitted to death, and works astonishingly well with vehicles of al sorts.

In fact, if you can find me a single case of it producing results out of line with any production vehicle tested by any major mag, produce it. I personally checked it in this fashion (unlike you, I don't blindly accept a calculator as being accurate without first checking its results to see if it actually works), and found it to be extremely accurate--as opposed to your beloved calculator, which I had no problem proving wrong looking up a few examples.

But given that you don't even know how to accurately calculate percent error, which a first-year engineering student can do in his/her sleep, I am not surprised at your ignorance of how to test an equation out.

You, otoh, are desparately trying to maintain that this calculator of yours is spot-on accurate, even after being confronted with numbers that any reasonable person would interpret as demonstrating inaccuracy on the part of the calculator...but instead, since you cannot admit error, you press on, attacking any and all data to the contrary of what your beloved calculator claims.

It's a rather sad spectacle....a reasonable person would have, when confronted with the data, simply admitted that in some cases the calculator clearly is wildly off the mark, but instead you come back at me with a cheap shot about "false assumptions"--and you have the gall to accuse me of beating a dead horse? Talk about a textbook case of pot/kettle.

Which is why you've been arguing about it for two pages now....right? Actions speak louder than words.

IFor higher displacement, low compression motors that can accept boost without detonation, it works reasonably well. But in other cases, it sucks.

Within 5%, yes, it will, and this has been verified experimentally.

No kidding? Really? The funny thing is here that you think you're educating me....but wheels aren't going to rob a vehicle producing "400 hp" of 10 mph in trap speed, that is unless you put tractor wheels on it.

And as pointed out before, the driveline in the suppsed "400 hp" Dinan M roadster is the same as the 333 hp version which magically managed to trap 2 mph higher.

So explain how a "400 hp" car managed to trap at 106, when the same car, same driveline, managed to trap 108 on multiple tests producing 70 less horsepower and far, far less torque.

Please, explain that for me.

The same. Duh....

The runs for Car & Driver are all altitude and temp corrected.

Except for one tiny thing: I've verified that this calculator works, under a wide range of horsepower ranges and conditions. And I've also verified that yours does not work, just by way of picking five cars.

Again: the results for the hp/trap calculator are accurate based upon manufacturers' horsepower ratings--yet for some reason, they suddenly stop working with certain tuners' bloated horsepower ratings.

But I'm sure that the flaw is with the calculator, not with some of the tuners overrating their cars. Yeah, that's it....I can, and have, run through the trap speed and weight in the tables in the back of the mags, pick out any car at random, and, using this calculator, get within a few percent of its rated horsepower, but with Dinan and your calculator it falls on the floor.

And this is obviously not a case of Dinan overrating their car, even though we also have further corroboration in the form of the 333 M Roadster (and in a separate test, the heavier M coupe) trapping 2+ mph faster with 70 less horsepower; oh, no, no no no no no, that couldn't possibly be it.

No, the only possible explanation is that your calculator is extremely accurate, even though results show it not to be accurate, and Hale's calculator is not, even though results show it to be accurate.

If it traps at a best (remember, C&D uses the best, not some arbitrary first-time run) of 108, then yes, that would obviously be the case.

Of course, were it a tuner, that would be fine, because, well, we've got this calculator that plainly shows that the little M Roadster *should have* made 400 horsepower, even though it got out-trapped by an M roadster with the same driveline, at the same weight, which was making 70 less horsepower.

Very plausible.

This isn't about skratch. It is about you trying to come off acting like you know what you're talking about, when the numbers plainly show you to be wrong, and continually attacking me even after the numbers show you to be wrong.

BlownV8

You are beating this to death. READ WHAT I AM WRITING. I COULD GIVE A RATS *** ABOUT THE CALCULATOR! I COULD GIVE A RATS *** ABOUT ARGUING WITH YOU ON A POINT BY POINT BASIS.

The calculator, I'm sure, is based off a widely accepted premise that for every bar of pressure you apply to an engine it will double in HP. Is that absolute - no. Is it worth a summary glance at what an engine will make when under boost - yes.

Here are a couple more calculators to determing RWHP. You can't use them to determing crank hp because you don't know what the driveline is robbing. THE ONLY WAY TO DETERMING CRANK HP WITH ANY DEFINITIVE ACCURACY IS TO RUN THE ENGINE ON AN ENGINE DYNO.

Probably not that accurate and these are not my formulas but can be used as well:

hp = weight / (ET / 5.825)3

hp = weight X (speed / 234)3

Take it for what it is worth but don't spend hours debating it because I don't care.

hooleyboy

Ive added aftermarket wheels with a dyno after and I lost about 20whp and that was going with a 18x9.5 rear, over stocks 18x8.5. On my next 1/4 mile pass I was down 3mph and was clocking at 106 rather than my standard 109mph. The wheels were a bit heavier than stock.

Improviz

Well, you've certainly wasted a lot of time arguing about it, for some inexplicable reason.

So stop.

As I said, and showed: results vary, and it seems to be much more reliable for engines with larger displacement and low compression--which makes sense, if you think about it.

Incorrect. Dynos have inherent deficiencies and inaccuracies; click here for a very good article on this subject.

Oh, wait....you probably meant a true engine dyno, where the engine is out of the vehicle...oh, well, article is a good read about chassis dynos, leaving it in. Anyway, yes, that's the best way, but for obvious reasons is impractical for most people. The Hale formulas are pretty good, and give a pretty accurate result in pretty much every case I've checked them against rated horsepower figures.

Btw, the equations you cite below are Patrick Hale's, and the second one is very strongly correlated (i.e., accurate) in providing crank, not wheel, horsepower for a vehicle of a given weight hitting a given trap speed.

The first one, not so much. Which is why I never use it. Trap speed is a *much* better indicator of horsepower than ET.

The second one works quite well; it is what I was using to check the results, and it provides crank, not wheel, horsepower estimates. If you cross-check it against traps/weights (including driver), it is normally within a few percentage points of a vehicle's crank hp, truly amazing. A lot of work went into fitting that curve.

It gave the first inkling that the 55k motors were vastly underrated horsepower-wise. For example, a 4350 pound E55 (including driver) trapping at 116 gives an estimate of 530 horsepower. With a 20% driveline loss, this would give you an expected chassis dyno number around 424 horsepower (although from C&D article, results may vary). Plenty of stockers are dynoing in that range.

It also makes sense from a pounds-per-horsepower perspective: 4350/530 = 8.2 pounds/hp. C5 Z06s, which trapped about 115-116 and would be at about 3300 with a 150 pound driver (same as I used for the E55), would come in at 3300/405 = 8.15 pounds/hp.

So here, the results make sense. If you use rated horsepower of 469, they don't. Just as when you see a 3800 pound Nissan GTR trapping at 122+ with 480 rated horsepower, it doesn't make sense...but this does:

BlownV8

Yes, that's why I said you have to put it on an ENGINE DYNO. I did not say chassis dyno.

Not arguing......just discussing:

The effect on higher compression engines is the same as on lower compression engines. Boost will make HP. The reason the higher compression motors are not making the same hp is due to tuning. It would be like putting headers, cams, and larger pulley on an engine and immediately saying it will make X HP. We know that it won't make the most hp uless you tune the engine management system to adjust for the extra airflow to maximize HP.

You can max the hp on a high compression engine or a lower compression engine. The reason the lower compression engines are producing more hp/lb of boost typically is due to tuning and fuel not due to the inability to make the same power given x boost. You don't have to live on the edge to get the returns on a low CR forced induction engine. However, to really max out the HP on a high CR engine, you will need a very good engine management system, with EGT sensors at each exhaust port with the ability to tune each fuel injector so the engine does not run too lean or too rich. If you are not running the right engine management system or the stock one does not have enough tuning parameters, you are risking a blown engine due to preignition exacerbate by the high CR.

Are we going to completely dismiss something as completely incorrect and worthless when you have tuning variables, fuel variables, supercharger efficiency variables, and intercooler variables? Maybe or maybe not. I guess it depends on your definition of a worth while estimator. I guess that's why something is called an estimate.......because it is not exact. Kind of like saying two objects regardless of their mass or shape fall at exactly the same speed........in a vacuum.

Here is what the formula really needs to include and an explination of each component to be much more accurate: http://stores.thunderhawkperformance...automotive.htm


BOYLE’S LAW


Boyle’s Law.

P = pressure, V = volume and T = temperature

(P1 x V1) / T1 = (P2 x V2) / T2

Any increase in pressure (P) will always result in an increase in temperature (T) or a decrease in volume (V).


Calculating the boosted air temperature discharged from a 100% efficient compressor but we know that 100% is not very accurate:

T2 = T1 x (P2 / P1)0.283

T1 = Inlet temperature (degrees Rankin); ambient temperature

T2 = Outlet temperature (degrees Rankin); air charge (boost) temperature

P1 = Inlet pressure (PSIG); atmospheric

P2 = Outlet pressure (PSIG); atmospheric + boost

Convert Rankin (R) and degrees Fahrenheit (F), use the following formulas:

F = R – 460

R = F + 460

Temperature increase using a compressor with 100% efficiency rating and caused by the above pressures increase in Fahrenheit):

T3 = T2 – T1

T1 = Inlet temperature Fahrenheit; ambient temperature

T2 = Outlet temperature Fahrenheit; air charge temperature

T3 = Ideal temperature increase Fahrenheit at 100% efficiency


EXAMPLE 1: 85° F inlet temperature, 100% efficient compressor, 7.5 PSI boost


Outlet temperature T2 = (85 + 460) x ((7.5 + 14.7) / 14.7)0.283

Outlet temperature T2 = (545) x(22.2 / 14.7)0.283

Outlet temperature T2 = (545) x (1.5102)0.283

Outlet temperature T2 = (545) x (1.1237)

Outlet temperature T2 = 612 (degress Rankin)

Outlet temperature T2 = 612 - 460

Outlet temperature T2 = 152° F



Ideal temperature increase T3 = 152 – 85

Ideal temperature increase T3 = 67° F




ADIABATIC EFFICIENCY
Boyle’s Law allows for the calculation of air charge temperatures created by a 100% efficient compressor. However, we know there is no compressor that is 100% efficient. Adiabatic efficiency varies from 50% to 80% for the compressors currently available in today’s turbo and supercharger systems.

q To calculate the actual temperature increase from a compressor:

T4 = T3 / AE

T3 = Ideal temperature increase (degrees F); at 100% efficiency

AE = Adiabatic efficiency

T4 = Actual temperature increase (degrees F); at adiabatic efficiency

q Calculate the actual air charge (boost) temperature from a particular compressor with known adiabatic efficiency:

T5 = T4 + T1


T1 = Inlet temperature (degrees F); ambient temperature

T4 = Actual temperature increase (degrees F); at adiabatic efficiency

T5 = Actual air charge temperature (degrees F); at adiabatic efficiency


EXAMPLE 2: 85° F inlet temperature, 70% adiabatic efficiency (typical supercharger, not intercooled), 7.5 PSIG boost



Actual temperature increase T4 = 67° F / 0.70

Actual temperature increase T4 = 96° F


Actual air charge temperature T5 = 96 + 85

Actual air charge temperature T5 = 181° F




EXAMPLE 3: 85° F inlet temperature, 76% adiabatic efficiency (typical performance turbocharger, not intercooled), 7.5 PSIG boost



Actual temperature increase T4 = 67° F / 0.76

Actual temperature increase T4 = 88° F




Actual air charge temperature T5 = 88 + 85

Actual air charge temperature T5 = 173° F


INTERCOOLER EFFICIENCY

An intercooler is designed to remove as much heat as possible from the air charge before it enters the engine. As is the case with compressor efficiency, no heat exchanger (intercooler) is 100% efficient.....uless you are using ice and then it can lower the temperature below ambient.


Intercooler efficiency is the measure of the amount of the temperature increase removed from the air charge before it enters the engine. For example, an intercooler which can reduce the air charge temperature by 80° F, in a system which increased the air charge temperature by 100° F over ambient, would be considered 80% efficient.


A properly designed air-to-air intercooler of sufficient size can achieve efficiencies approaching 90% without ice. With an air-to-water intercooler system, two heat exchangers are required as explained in the text. Therefore, the total system efficiency is the multiple of both heat exchangers’ individual efficiencies.

q To calculate the final air charge temperature entering the engine with an intercooled forced induction system, use the following formulas:


T6 = T4 x IE


T4 = Actual temperature increase (degrees F); at adiabatic efficiency

IE = Intercooler efficiency

T6 = Temperature decrease (degrees F); due to intercooling


T7 = T5 – T6


T5 = Actual air charge temperature (degrees F); at adiabatic efficiency

T6 = Temperature decrease (degrees F); due to intercooling

T7 = Final intercooled air charge temperature (degrees F)



EXAMPLE 4: 85° F inlet temperature, 70% adiabatic efficiency, 65% efficient air-to water intercooler (typical supercharger with liquid intercooler), 7.5 PSIG boost



Temperature decrease T6 = 96° F x 0.65

Temperature decrease T6 = 62° F


Final intercooled air charge temperature T7 = 181 – 62

Final intercooled air charge temperature T7 = 119° F





EXAMPLE 5: 85° F inlet temperature, 76% adiabatic efficiency, 88% efficient air-to-air intercooler (Thunderhawk Performance intercooled turbo system), 7.5 PSIG boost



Temperature decrease T6 = 88° F x 0.88

Temperature decrease T6 = 77° F


Final intercooled air charge temperature T7 = 173 – 77

Final intercooled air charge temperature T7 = 96° F

CONVERTING CFM TO LBS/MIN AIRFLOW



q At 85° F and 28.4 in. Hg., CFM can be converted to lbs/min by using this simple formula:


Lbs/min = CFM x 0.069

By referring back to Boyle’s Law, it is obvious that the volume (CFM) will increase with a corresponding increase in air charge temperature. However, this increase in CFM provides NO additional air mass. Therefore, there are no additional oxygen molecules made available to the engine for combustion, although the volume (CFM) is significantly higher.



Using CFM as a measure of airflow confuses the calculation due to the wide variations in temperature, both before and after the compressor, as well as after the intercooler. All calculations in this technical manual assume the above conversion standards. However, to accurately compare compressors, the compressor efficiencies as specified in the compressor flow maps must be known in order to calculate density and bring all compressors back to this standard.

Improviz

....keep in mind that MB, BMW, Audi, Subaru, others all have engine management systems of the type you describe, and yet all invariably lower the compression ratios of their engines in turbocharged applications.

Detonation is the reason, and clearly, even with all of the tools at their disposal, they don't feel that going beyond a certain point is prudent.

Certainly, one can introduce higher boost into a lower compression motor without introducing detonation. If you figure an engine takes a 8% hit for each point reduction in compression ratio but gains 7-8% for each pound of boost, then you can lower the compression ratio to 9:1 and make up the difference with a bit more boost...but if you've got it at 11:1 or 12:1, then you've got much lower margin. On DI cars you can run higher boost w/o detonation, but this calculator isn't restricted to DI engines.

There are tricks such as water injection, etc. that you can do to avoid grenading the engine, but on the whole it's safer to use lower compression motors, which is why the manufacturers do it. They've got to warrant those motors.

In fact, Garrett turbocharger designs recommends lowering compression ratio in high-boost applications; I'll highlight a few pertinant quotes for emphasis:
And that's the thing: this calculator doesn't allow for this fact; it simply assumes a certain amount of boost can be stuck into a motor, regardless of the design of the motor.

It is because of this, along with other factors not factored in previously discussed, that I find that calculator to be kind of a hit-or-miss enterprise, at least in terms of practical applications. And Garrett would seem to reinforce that view. In a perfect world (or one where the tuner has a multimillion R&D budget ) you could have your cake and eat it too via high compression and high boost, but in reality the low-compression motors will always give you more margin, and thus more potential for power gains with less danger of grenading.

Thanks for the refresher course in Boyle's law, studied that in school, now I'll have nightmares tonight.

BlownV8

Most manufacturers lower the compression for engine longevity and dependability in a forced induction application. Modern engines run high CR's for good power without forced induction. They have to warranty the engine and don't want to replace them very often. Yes, ideally, you don't want to run high CR's in a forced induction engine but it can be done but like I said it is not ideal. In fact, most manufacturers usually run CR's that are lower than ideal for forced induction because they want a margin of safety.

Many people often use detonation to describe what kills engines but the real insideous killer is pre-ignition. Detonation and pre-ignition are completely different; however, they are both issues with abnormal combustion that you don't want. The higher the hp/cubic inch the greater the damage from detonation. Low CR engines can run with continuous detonation for a very long time without serious issues. With detonation, you get warning signs but with pre-ignition all you get is engine damage.

An engine can suffer from detonation for, often, great lengths of time without failure. However, the damage from extended detonation causes broken ring lands, broken spark plugs, overheating and scuffed piston skirts, as well as pitting of the piston crown much like sandblasting would appear. Detonation occurs after the spark plug fires and usually occurs well past TDC when the piston is on the down stroke. You get that sound as if someone is beating on your heads with a hammer - PING! Detonation also causes EGT to DROP. Any drop in EGT's from your norm should be a warning for detonation.

Pre-ignition is the ultimate killer of an engine. You get no warning what so ever. Usually, all you get is a grenaded engine. When the fuel mixture ignites prior to the spark plug firing, you have pre-ignition. A glowing spot in the chamber is the usual cause for pre-ignition and can be a plug that gets too hot or even a carbon ember. The amout of stress on an engine during pre-ignition is tremendous. The piston is pushing up on very hot mass of expanded gas and it puts tremendous stress and tremendous heat onto the parts. Holes in the pistons or spark plugs that are melted are also sign of pre-ignition

You are welcome and it wasn't my favorite either.

Improviz

Right, because they don't want to deal with engines damaged by detonation.

Detonation is caused by excessive heat and pressure causing the air/fuel mixture inside the combustion chamber to autoignite. Pre-ignition is also caused by excessive heat (in fact, pre-ignition can be a source of detonation), and either can damage the engine. and remember: the more compression, the hotter the air, so the likelihood of both is increased with increased boost in conjunction with higher compression.

Yup. Either one can damage an engine, but pre-ignition does it faster and worser....

They can also be caused by detonation. Either one can introduce serious damage to an engine, although it will occur much more quickly with pre-ignition. Here's some interesting material:
Also, the likelihood of engine damage from detonation is significantly higher as the engine's specific output increases:
http://www.streetrodstuff.com/Articles/Engine/Detonation/Page_2.php
Here he discusses how detonation can cause pre-ignition:
So, ymmv, but I'd avoid boosting a high-compression engine like the plague.

Cylinder Head

iTrader: (1)

Amen, that's why I have the best of both worlds. 2JZ and S85 FTW!!!

P.S. I avoided the last 20 posts because you need an astrophysics degree from MIT to understand them.

ProjectC55

Good Stuff!