standard drivetrain loss

[kahmann]

What is the standard drivetrain loss for the SGT?

I've heard anywhere from 12% to 19% from some reputable people whose opinions I trust.

I was told by AFBLUE in my last dyno thread that it's 12%, based on the fact that several SGT's base dyno'ed at around 280 RWHP. Taking into account the advertised 319 crank HP, you come up with about 12% loss. Are all of those STD or SAE #'s? Is the 319 crank HP verified by some sanctioning body? I honestly don't know how that works, but if not accurate, the actual flywheel # would probably be less than the advertised HP, further confusing the issue.

 

In the April 08 edition of Motor Trend, however, they run a comparison test of the 08 SGT against the Roush Stage 2 and the Saleen S281-3V. They dyno'ed each car to compare and mentioned that they would be "expecting a 15% loss due to drivetrain inefficciencies." The SGT-C that Motor Trend was using pulled 273 RWHP on their corrected dyno. Assuming that the advertised 319 HP is accurate, then the drivetrain loss on that SGT-C was just a hair below 15%.

 

So which is it? This has always been kind of novel to me when running my SGT on the dyno, because a higher drivetrain loss meant that the final crank HP would be higher. So after hearing 17%-19%, I never looked back!

My 347 RWHP would equal 420 crank HP based on 18% loss, but would only equal 409 HP based on 15% loss or 400 HP based on 12%, which simply means less bragging rights I guess. Nothing too important.

But now that I'm about to install a supercharger on an already modified engine (with stock internals), this calculation has become much more important to me, since it will help determine how much boost I inevitably operate the blower at.

 

Two final points:

1) Regardless of what the actual drivetrain loss is generally accepted to be for the SGT, is the % any different for the GT500? If so, why?

2) Is there a dyno sheet thread in the SGT section of the forum? If so, I can't find it. Perhaps it would be useful for all of the guys that have had their SGT's on a dyno to post their #'s and sheets in a dedicated thread (especially base dyno's)?

 

Thanks for any and all input, citations, or experience.

 

Ken

[GT500-07]

good question, I've been told 15% by some and 18% by others for SGT or GT500. Then last week end while test driving a CSX I was told it was 12% on them because the drive trian is so short.

[Radical08]

Typical loss on a manual is 15% and auto is 18%.

[blueone]

I've had my car dynoed twice, both times it was on a in ground Dynojet after my blower was installed but the shop who is building my new motor uses a MD1750 and has already told me that my numbers will be lower on their dyno but will be more accurate for the reasons listed in the link below. I would like some opinions on the differences in accuracy between different dyno manufacturers.

 

http://www.mvperformance.com/catalog/index...2&chapter=3

[AFBLUE]

Typical loss on a manual is 15% and auto is 18%.

This is an average/rule of thumb for all vehicles. Obviously a F-350 is not going to have the same drivetrain loss as a Mazda Miata.

[AFBLUE]

I've posted quite a few time about this subject in the past. The 2 EPA runs on done by SAI back in Dec 06 were 319 and 320 at the crank on 91 octane gas.

 

We don't know what this partular engine would have done on a dynojet, but we do know some stock dynojet numbers from TS members.

 

SGT Stock Dyno #s

Shelby GT #0779 279

CudaFly 281

Ed S #571 276

Ed S #571 280

Lulu 276

SGT#507 275

mastersmech1 285

 

If we use 275rwhp we get 16% loss (275 x 1.16=319) If we use 285rwhp we get 12% (285 x 1.12=319). Based on this small sample it's somewhere between 12-16%.

 

Having said all that, I read an article about a dyno operator with a lot of experience dynoing F-150s. What was interesting was his before and after engine swap runs going from a 4.6L manual to a 5.4L manual. The drivetrain was unchanged so according to the percentage theory, the % should have stayed the same. But it didn't. What stayed the same was the actual horespower loss (not the percentage)

Now in the manual-tranny vehicles, the 5 & 6-speed manuals tend to lose (in round numbers) about half as much power as the automatics do - so a typical 220 HP non-PI 4.6 5-spd. 1997-1999 F-150 sees about 185 RWHP in stock trim on an ideally-running stock truck, just for example (though we've seen a number of them hit only 170-175 stock). So now we're talking about a 15.91% loss. But drop a 5.4 260 HP motor in that same truck as a number of our customers have done so that they can have a 5.4 manual-tranny F-150 (which Ford doesn't make), and the driveline loss stays close to 35 HP (it might hit 38-40 HP), which then represents a 13.46% loss.

http://www.f150online.com/forums/sho...6&postcount=13

 

This tells me that using the percentage method for drivetrain loss is flawed. If it worked, the the percentage should have been the same for both runs on the same vehicle/drivetrain.

 

Based on the above, unless you change component in the drivetrain, it may be more accurate to add 40 +/- 5hp to your dynojet SAE numbers to get your crank number.

 

Here's another interesting read titled "The absurity of fixed % drivetrain loss" http://forums.tdiclub.com/showthread.php?t=75062

The whole concept of a fixed percentage drivetrain loss in evaluating chassis dyno tests is one of the most absurd things i've ever heard of in my experience as a powertrain engineer, and is the motivation behind this post.

 

First, a primer: energy (or in the case relevant to this discussion -- power) cannot be created or destroyed. Simple enough? Where then, does that power that is transmitted from the crank, to the wheels, and ultimately to the road, go? Most of it goes to friction and therefore heat.

 

Second, an illustration: For argument's sake, take a stock 90HP TDI, and we'll arbitrarily say that it has a 15% driveline loss. That means that the engine would be developing about 104HP (90/1.15) at the crank. The loss through the drivetrain was 14HP (104-90). Now, you do a bunch of engine mods without touching the drivetrain, and you now measure, say, 135HP at the wheels. Adding the customary 15% to refer back to the crank, you get 155HP, but the loss through the drivetrain is now 20HP, a difference of 6HP, WHEN NOTHING HAS BEEN TOUCHED THERE!

 

Do you now see the absurdity of this concept?

 

Firstly, may I submit that 2WD vehicles with manual transmissions have very good mechanical efficiencies, as evidenced by the fact that 2 quarts of non-pressurized, non-circulating oil is sufficient to keep the entire transmission cool and lubricated. In fact, to attach a number to it, manual transmissions are usually over 90% efficient, and many over 95%. That implies a loss through the transmission of between 5.3-11%. Even the best automatic transmissions with lock-up TCs achieve between 80-85% efficiencies.

 

Secondly, may I submit that contrary to popular (mis)conception, flywheel weights, rim weights/diameters and tire type (should) have very little contribution to the HP numbers on a rolling road dyno. Heavy flywheels and rims act as inertial dampers but do not destroy or create energy, nor transform it to heat, as would have to happen to if it is to result in a greater or lesser HP value on the dyno. Tires will shed energy in the form of heat by the simple contact with the ground and also though the flexing of the treads and sidewalls, but this amount is negligable in the scheme of things that it is generally ignored unless you are an engineer for an OEM, race car team or tire manufacturer. More on inertia in a moment.

 

Thirdly, I hope the above underscores that an accurate measurement of drivetrain loss cannot be overgeneralized. For one, it is not constant across the entire measurement range within a given run. In fact, friction increases roughly linearly with speed. In automotive engineering speak, this is quantified by a parameter called the FMEP (friction mean effective pressure), and although it's is not called that, it is manifested in many engine graphs you may read without even realising it. Frictional losses are different at 2000RPM to 4000 RPM, etc., etc. You cannot, therefore, equate the drivetrain loss of a car whose engine is turning at 8000RPM at the maximum rated power to one turning at 4000RPM, because on the basis of the RPM alone, frictional losses at 8000RPM are roughly double that at 4000RPM.

 

That said, yes, it's true: gear selection when performing a rolling road dyno DOES have an impact on HP, but it is not usually borne in dyno results, because the difference is small and within the inevitable variation from test-to-test and also measurement error.

 

Further, engine/driveline design considerations mean that there is a wide variance in frictional losses between different cars; the comparison of mechanical efficiencies between manual- and automatic transmissions have already been discussed above. Cars with AWD, automatic trannies, and large-displacement/many-cylinder engines will tend to have higher frictional losses than small-displacement, 2WD, manuals.

 

Finally, The importance of "motored" or coast-down tests in a dyno evaluation is important and needs to be stresssed, because that is what accounts for your true frictional losses and balances the inertial "ledger sheet" of the different driveline components, including the wheels and tires. The energy that is absorbed in the form of inertia in the flywheel/wheels/tires, etc. is accounted for ("given back," to oversimplify) in this coast-down, and when doing a street (i.e. butt) dyno, also accounts for the very important aerodynamic drag.

[kahmann]

My head hurts after reading all that AFBLUE!

Definitely some great info, though. Makes me second guess just about everything I've assumed, heard, and thought I knew. Thanks a lot man.

[AFBLUE]

I hear you.

 

The underdrive pulleys like the drivetrain reduces the amount of hp that reaches the wheels. Whether we swap out the UDPs on a stock 180rwhp 96 Mustang GT or a stock 2007 280 rwhp Shelby GT, we gain about 10 hp at the wheels. 10hp is a 5.5% increase for the 96GT. If I took the SGT 280rwhp and multiplied it by 1.055, it would give me 295rwhp rather than the actual 290rwhp gain.

 

So why do we assume that using a percentage for a drivetrain will give us an accurate number when we add superchargers or other performance mods?

 

Just like in the example above where they swapped a 220crank hp/185rwhp 4.6L out for a 260 crank hp/225rwhp 5.4L in the same truck with the same drivetrain. While the percentage of drivetrain loss was different (15.91% for the 4.6L vs 13.46% for the 5.4L), the actual hp drivetrain loss was remained constant at 35hp.

 

Thus, if the drivetrain sucks 40hp (+/-5hp) from crank to the wheels on a stock SGT, it will probably be about the same on a supercharged one. Why wouldn't it be?

 

I'm no expert on this, I'm just reading what others have said on this subject over the last 6 years (when I got my 96GT dynoed for the 1st time)

 

Here's another good read on this from a much smarter guy

Dave is correct that driveline loss is not really a "percentage". There is a component that's proportional to the torque transmitted (friction between the gears and in the bearings - but the bearings are all rolling-element and gear-sets are typically 98% - 99% efficient except maybe for hypoid rear-ends that are a bit less). If there are two gear-sets to go through and no 90-degree gearsets, which is typical of transverse front-drive gearboxes, then the mechanical efficiency of the gears not counting other types of losses can be in the 97% range.

 

There is a torque component of the losses that depends on the rotation speed (typically, churning and pumping losses of the lubricant - these losses increase with rotation speed but aren't affected by how much torque is being transmitted), and there is a torque component of the losses that is almost constant regardless of rotation speed or torque transmitted (typically, sliding friction in seals). And automatic transmissions have complex patterns of losses (typically much greater than manuals) due to the torque converter and the pump that operates all the hydraulics.

 

There are things that can be done about some of these losses (different lubricant viscosity, for example) but much of it is set by the design - nothing can be done about it other than different lubricant viscosity or oil level, and that's limited by what is specified by the manufacturer. Bottom line: Transmission losses are there, they vary and are not a set percentage, and little can be done about them, so the most suitable course of action is to simply not pay attention to it and only pay attention to wheel horsepower.

 

The bit about wheel and rim weight and other inertial loads deserves comment: how much difference this makes depends on what type of dynamometer is used. If a brake dyno is used, in which speed can be held constant while the torque is absorbed by a (typically) water brake, then Dave is correct, nothing you do about the inertia will make any difference at all. But if the most common aftermarket-type dyno is used (the Dynojet inertial dyno, or similar) then inertia of those parts CAN and WILL make a significant difference.

 

Finally, the most complex element of all: Like it or not, there are variations from one dyno installation to the next. Some of it is variance due to the dyno itself, but Dynojet claims that it's small. Cycle Canada did some testing a while back which found that perhaps the variation is greater than Dynojet admits to. For sure, there are variations due to the installation, and there are variations due to the way the testing is done, and there are variations due to temperature and barometric pressure.

 

If you are doing serious tuning, then comparison tests should always be done on the same dynamometer by the same operator using the same test procedure, and preferably under ambient conditions that are as close as possible. Comparisons between different dyno installations aren't really valid.

http://forums.tdiclub.com/showpost.php?p=7...mp;postcount=12

[wmoore]

 

TMI...QP told me I had 535 at the crank and 455 HP/444 TQ at the rear wheel (corrected). I was told the numbers before correction was 471/461. I say just go with the dyno sheet and keep it simple but, then I guess it's a game of...which dyno and what kind.

[AFBLUE]

The only way you are going to truely know your crank hp is to put it on an engine dyno...very expensive and time consuming compared to a wheel dynanometer.

 

As you make changes to your car, the key is using the same dyno so you can compare apples to apple.

[kahmann]

The only way you are going to truely know your crank hp is to put it on an engine dyno...very expensive and time consuming compared to a wheel dynanometer.

 

As you make changes to your car, the key is using the same dyno so you can compare apples to apple.

+1

Same shop, same dyno, same correction. But then your only apples are your own dyno pulls.

[wmoore]

The only way you are going to truely know your crank hp is to put it on an engine dyno...very expensive and time consuming compared to a wheel dynanometer.

 

As you make changes to your car, the key is using the same dyno so you can compare apples to apple.

 

 

An engine dyno? But, we still have the debate about rear wheel HP with just an engine dyno. Aren't the rear wheel numbers the important ones?

[AFBLUE]

An engine dyno? But, we still have the debate about rear wheel HP with just an engine dyno. Aren't the rear wheel numbers the important ones?

I agree that the wheel hp is the important one. My point was to attempt to answer the question that started the thread. If you want to know exactly what your drivetrain loss is for your engine you would have to test it on an engine dyno and a wheel dyno. Otherwise it's just a guessing game.

 

The best we can do now is an estimate based on the EPA tested SGT engine that achieved 319-320 and that SGT engines on a dynojet produce 280rwhp (+/- 5hp) SAE on average...or 40 hp loss in the drivetrain.

[clark17357]

While the "loss" question is interesting, it can be mind numbing. The numbers that matter (to me at least) are my rear wheel torque and horsepower (in that order) numbers.

 

Jim

[Radical08]

While the "loss" question is interesting, it can be mind numbing. The numbers that matter (to me at least) are my rear wheel torque and horsepower (in that order) numbers.

 

Jim

 

 

I don't get all wrapped up in what loss I had and can't control that mush anyway. After my Whipple install I lost 14% crank - wheel. A dyno is the quickest and easiest way to see loss and what is at the wheels and is close enough for anyone's needs, I would think. :happy feet:

[one_quik_pony]

I don't get all wrapped up in what loss I had and can't control that mush anyway. After my Whipple install I lost 14% crank - wheel. A dyno is the quickest and easiest way to see loss and what is at the wheels and is close enough for anyone's needs, I would think. :happy feet:

 

How do you know you lost 14% without the use of an engine dyno?

 

Are we going as far as to figure in the horsepower lost by turning the Whipple?

 

A good example of why those two theories aren't correct would be the installation of a lightweight driveshaft. You don't GAIN horsepower from it, but you lose less energy (torque) by spinning up less mass, resulting in higher horsepower (calculated from torque) numbers.

[HORSBYT]

And you lose even more if you're running 4:10's........

[kahmann]

And you lose even more if you're running 4:10's........

I didn't even consider gear ratio. I was running 3.55's on my first pull and 4.10's on the last go around.

 

Ken

[HORSBYT]

I didn't even consider gear ratio. I was running 3.55's on my first pull and 4.10's on the last go around.

 

Ken

 

 

Yeah, my shop (a featured install shop in all the Mustang mags) told me that i'd lose 15-20RWHP due to the 4:10's. I asked why and it had something to do with how the wheels are turning the drum and at what speed, etc. The obvious trade off with 410's is the gain in torque which you obviously give up HP for. So hard to always have your cake and eat it too!