Do the chassis dyno setups have some method of determining the hp/torque at the crankshaft? If not, I'm not sure where he gets the 12% from if all he does is run cars on the chassis dyno. The drivetrain loss factor is the amount of power/torque lost after the engine. The amount of grip between the clutch and flywheel, the gearbox, the driveshaft, differential, axles, rear suspension, and even the wheels/tires can play a role in this loss factor. Tillmanspeed said this factor was 16% (I originally said Doug by mistake).

 

As you know, that would involve removing the engine, running it and testing it on stands, refitting it, then running it on the rollers, on the same day or at least in similar conditions. So no, not many people do that. His method, as I explained, is comparing stock dyno numbers to manufacturer's (engine output) figures over a large sample. Knowing that manufacturer's figures vary, and engines vary and accounting for that in the large sample's mean is the best anyone can do without the exhaustive process outlined above. Tillmanspeed's 16% and the suggested 12% differ by 12hp on the 300hp GT. 252 vs 264 if 300 is correct. A lot of s197s are showing 10-15hp above even the 264, which suggests the engine output is well underrated (5%) but within tolerances. If the 16% figure is closer to the truth, then the margin of underrating is close to 10% of total output, which seem to be wild engineering tolerances. I don't care either way, but 12%, given the evidence, seems more realistic than 16%.

 

I'm not saying that 12% is the wrong factor, but I am saying that the method used to derive this figure (thus far in this thread) isn't solid.

The OEM would know the actual factor due to the amount of testing they have conducted. Like I suggested earlier in this thread, the only surefire way that I know to determine this value is to run the engine on an engine dyno, then drop that motor into a S197 GT and run that on a chassis dyno. Until someone does this or has the data to back it up, 12% is still speculation and far from "confirming" the actual factor.

Like I said before, the 2000 Ford Crown Victoria was advertised to have 215 hp. Those "in the know" knew about Ford using retarded timing, and only achieving roughly 160 rwhp on the chassis dyno. The drivetrain loss factor was already known, so Ford over-rated the advertised hp by 28 horsepower!

 

I say the 12% is observed from repeated experiment, given the physics associated with engineering tolerances, making a claimed engine output figure +/- 5% (at most) away from any individual motor's actual output at the crank (which makes it a soft constant). Plus, we have observed rwhp data that supports the theory. So it's far from speculation, in my view, it's observation.

The Crown Vic example is messed up because of the supposed ignition retardation. We have no actual motor output number to work with.

 

As opposed to your dyno operator's repeated experiments dealing with RWHP and not engine output?

The 98-99 Crown Vic is identical to the 00 Crown Vic. It was shown repeatedly that the 98-99 Crown Vics will dyno 180-183 rwhp, and it was known that the drivetrain loss is slightly under 15% (through OEM conducted tests). Almost everything is known. The 00 Crown Vic is just an example of how the advertised horsepower can be completely wrong. Had someone used that advertised figure as a baseline, they would have assumed a loss factor of around 25% (incorrect for Panther 4R70W w/ TC locked in 3rd gear).

AFBlue and your dyno operator are guesstimating the losses using the advertised horsepower as a baseline. You can sit there and run 30,000 chassis dyno tests and still not come out with the right answer because you haven't isolated the engine from the drivetrain.

 

Stupid question: Is the 12% number the same on Automatics as it is with Manuals? Just curious.

 

no, so that would be a reason why a crown vic would show higher then 12% also.

Autos soak up more hp so loss is higher %

 

It's more than a guess, it's the manufacturer's supplied number. Ford are not guessing. There are variations, but these are within close parameters.
You can quote a thousand crown vic examples to me, but you already stated that something else was changed between supplying that number and the actual testing, i.e. the ignition remap. You are right, the pure scientific experiment you suggest would be the only sure fire way of knowing for certain, but it's unreasonable in the real world. I'm happy with the manufacturer's numbers plus dyno testing for my purposes - YMMV.

To get back to the OP's interesting point, in my opinion, a mean of a small sample giving you a value within 2% (306) of the supplied number of 300 is remarkable but only because it doesn't vary as much as I would expect. As you know, mine is also in that range at 276hp, at 12% that's 309 at the crank, that's only 3.5% out. Where are the dynos with manual GT stockers only putting out 265, which is 3.5% the WRONG way... 'Friday afternoon' engines?

319 for the Shelby may be an indication that during testing, they couldn't quite average out a 20 with the 'sports' tune (which has its own variables on top), so gave the actual tested mean number instead of the original guesstimate 325. Rounding down not acceptable anyway for other reasons.

That's probably why Ford go conservative on the Mustang rating, to allow more headroom for SE/tuner stuff.

 

The Crown Vic's 4R70W was about 14.5% (Torque converter locked in 3rd gear).

The standard rule of thumb was 15% for manuals and 25% for automatics. Needless to say, they've improved on automatics with the lock-up torque converter.

 

Ford does conduct more testing than the average dyno operator, but the advertised horsepower (which people are using as GOSPEL in this thread) is not the same as the designed/expected engine output level. Equating a 12.2% loss from an average of 270 rwhp with 300 advertised horsepower isn't going to be accurate especially if you're basing it on what a chassis dyno operator guesstimates.

Surefire way to answer the question or find out the drivetrain loss:
Use engine dyno to determine engine output
Plop that motor into a S197 GT (stock drivetrain, stock suspension)
Run that vehicle on a chassis dyno
Use arithmetic

It'll be much closer than using under/over-rated advertised engine outputs or Swiss dyno operator guesstimates.

 

Why is drivetrain loss given as a percentage of the flywheel HP rather than just a flat number?

It doesn't make sense to me, if you consider two different motors that use the same drivetrain.
For example, replace your 300HP motor with a 400HP motor, and your drivetrain remains the same, assuming %25 loss (automatic trans), then your calculated drivetrain loss would go from 75HP to 100HP.

I'm not saying you're wrong, i'm only saying I don't undertand it. Please explain it me.

 

25% for the Automatics? So, if I dyno's at say 285 HP with mods of course, I would be over 350 at the Flywheel? That is hard to believe.

 

That was an OLD rule of thumb, probably derived before widespread use of a lock up converter (or the dyno operator simply didn't bother to make sure the converter was locked up in the 1:1 gear ratio). Again, you can't go by these estimates because the 4R70W (a 4-speed auto used on the 99-04 GT and 96-up Crown Vic) demonstrated much less parasitic drag than 25%, mainly due to the use of a lock-up torque converter. The manual transmission still relies on a clutch so it can't be too far off from the 15% estimate.

 

Thanks. But I do like the sound of 350+ HP. LOL. This has been an interesting thread and I learned a lot. Thanks guys!

 

If the Crown Vic auto tranny is 14.5% loss, then explain to me how a manual tranny is about 16% loss??? That makes NO SENSE. AT ALL.

 

In pondering this a little more, It occurred to me that if you take the "lowest"
number a Manual GT has dynoed, (Out of the examples given earlier 258 was the lowest) that car has to make 300 hp flywheel, else Ford is open to another fiasco like the 99 or whatever Mustang it was that didnt make advertised hp and wound up in some kind of litigation.

258 if I did the math right would be a 14% drivetrain loss and 300 fw hp.
275 which was the highest example you listed at 14 % loss from fw to rwhp would come in around 338 fw hp.
Sounds a little high but consider this also.
Every Manual GT wont have the exact drivetrain loss due to the same considerations that apply to the Motor. Variables in assembly tolerances, bearing variances, rear gear specs etc etc etc......

Seems to me this whole thing of % of loss hp from fw to rw hp is a dog you could chase for ever.

 

Neil, I think you are on to something here. This article about rwhp vs rated hp for the Ford Lightning and F150 illustrates that your train of thought is being backed up by dyno results.
http://www.f150online.com/forums/sho...6&postcount=13
Goes along with Neil's point. In the above F150 examples it would appear that using a horsepower set # loss for a given drivetrain, rather than a set percentage loss has more consistency.

Using the manual F150 with the 4.6L or 5.4L, they both lost 35 horsepower going through the drive train to the wheels.

So on a Manual Mustang GT, if we assume that 271 rwhp is the average rwhp (avg I got for 20 TMS stock manual GTs), and it has the same drivetrain loss as the Shelby GT (39), then we get 310 at the crank.

 

Yes, but there are tunes and tunes I ran my car with the FRPP power-pack and FRPP tune (Basically same setup as the Shelby GT minus the X-pipe) and I couldn't feel much difference compared to stock. With the same setup, a Brenspeed tune completely transformed the car and pulls much harder with no throttle lag, etc. So from what I've experienced, the FRPP is ultra-conservative, and I wouldn't expect the same gains that other tunes will give you.

So IMHO it wouldn't surprise me if the GT is underrated, the shelby GT is making slightly more than the GT at the crank, but Ford decided to keep a safety blanket and advertise lower than actual output to cover their a$$.

 

You are beating a dead horse. Go and do the experiment if you feel so strongly about it. The nationality of my mechanic is irrelevant. In my opinion, you are being a bit of a **** for reasons only known to yourself.

 

Just found this post by Amyb.
http://forums.bradbarnett.net/showpo...&postcount=213

So I think it's safe to say that the flywheel hp is confirmed by the EPA to be 319 or 320 hp. If folks are averaging 280rwhp on a dynojet (seen SGT dyno results: 1 was 279rwhp and the other was 281) then that is a confirmed 39-40 hp loss through the drive train (the same as on the Mustang GT).

So based on the info I posted in post #57 of the this thread, I believe you simply add 40hp to your SAE corrected dyno HP to get your flywheel hp.

Or for those who are not convinced by post #57 and still want to use a percentage, then that would be a 12.2% drivetrain loss.