Bare with me here.

A lot of folks think that the stock Mustang GT has more than 300 hp at the flywheel. This is primarily based on the stock dyno numbers. Traditionally 15% loss has been used when converting from flywheel to rwhp.

I took 11 stock manual Mustang GT dyno readings and they averaged out to 269 rwhp and 289 rwtq

I've also seen 2 dyno readings for 2 different stock manual Shelby GTs and both were really close.

1st one had 279 rwhp and 299 rwtq
2nd car had 281 rwhp and 301 rwtq

So let's just assume that avg Shelby GT has 280 rwhp and 300 rwtq.

Ford and Shelby originally had the flywheel hp for the Shelby GT listed at 325. Then they changed it to 319 hp. Unlike the 300hp # for the Mustang GT, this sounds like a rather precise flywheel hp number. They could have rounded to 320 but they didn't.

So if the flywheel hp for a stock Shelby GT is 319 and the stock rwhp is 280, then it has a 12.2257 drivetrain loss % http://www.geocities.com/da_toy_gti/power.html

So if the same drivetrain loss is true for a manual mustang GT (why wouldn't be?), then a 269rwhp mustang would come out to 306 flywheel hp and 330lbs of tq.

I had heard that automakers had improved drivetrain losses over the years, so maybe the new loss for conversion for a manual trans is closer to 12% rather than 15%

 

really cool and intereting analysis...

food for thought...hmmm.....

thanks!

 

It would not suprise me that the driveline losses are less now than they were even 10 years ago. Synthetic fluids in the tranny and rear end will help a lot, as well as any other tweaks that have been done to maximize fuel economy.

 

I think your right twice. First, I think your right in believing the drivetrain loss has been reduced over the years, for what ever reason. Second, I think your right in assuming that the stock GT actually has a little more than 300 hp. Since we know the dyno numbers and we know the advertised numbers, there is no reason to believe the same % loss in the Shelby is equal to the % loss in the stock GT. Shelby does nothing to the drive train when upfitting the GTs to there specs, so there is no reason to believe that a Shelby has less % loss in the drive train than the stock GT.

However, a 12% loss from flywheel to tires would result in 306 HP at the flywheel, while a 15% loss would result in 316 HP at the flywheel. So for the sake of my ego, i'm gonna keep assuming that 15% loss and just say ford underrated the HP numbers for EPA standards which will remain nameless.

 

This also should bring up the point to people who do drivetrain mods like pullies and flywheel and driveshaft that they're reducing the loss % instead of increasing power.

 

I think the original poster is right on the money. Another thing that would back this up is the fact that many of the first '05 models had the precat device installed in the intake. It was pretty restrictive and I remember seeing a couple of before and after dyno tests showing a few more hp at the rear wheels after it was removed. To the best of my knowledge late '05s and beyond don't have this device yet the hp rating stayed the same.
As we all know removing a restriction from the air intake, especially one as bad as that one was is sure to increase hp even without a different tune.
The other thing to consider is that a manufacturer is safer to publish hp ratings that are lower. I remember a few years ago there was a lawsuit with some model of Mustang (don't remember which one) where the car wouldn't produce the factory rated numbers and Ford got into a lot of crap over it.
So it wouldn't suprise me at all to know that Ford is going on the side of caution with thier hp numbers.

 

I believe Doug said the TR-3650 has about a 16% loss in 4th gear for the S197 GT.

As a comparison, the 4R70W has a drivetrain loss of around 14% in 3rd gear w/ the TC locked for a Crown Vic.

The big lawsuit was over the 1999 Ford Cobra because it needed a bunch of recalls to even get close to the advertised horsepower. The 2000 Crown Vic dyno'd 160 rwhp whereas 98-99 Crown Vics were at 180+ rwhp. Since almost none of the Crown Vic buyers (police/fleet, old people) regularly dyno their cars, Ford got away with advertising 215 hp at the flywheel.

 

i put 272 hp at the tires and 295 tq on my car when it was 100% bone stock. So....15% is like 320 hp

 

Mark,

If I reduce the stock 300hp by 12.2257%, I come up with 263hp. That is exactly where my stock GT (1,650 miles) dyno'd at last Sunday.

 

The advertised horsepower will rarely end up the same as the actual engine output. If anything, Ford will want to slightly underrate the Mustang horsepower (after the 99 Cobra fiasco).

One way to find out for sure is to have the engine hooked up to an engine dyno, and then to stuff the same engine into a S197 and run that on a chassis dyno. Keep in mind that whatever percentage is derived is only applicable for that exact powertrain/drivetrain setup and will vary due to manufacturing variability.

 

FYI: Here are the 11 stock manual GTs I used to get an 269rwhp average.
Name rwhp rwtq, dyno type, trans
06VistaGT 265 286 Manual
1st Stang 272 288 Dynojet Manual
dallasw77 270 ? Manual
DaTT(1sK) 273 296 Dynojet Manual
FordRacing 275 290 Manual
karman 271 295 Dynojet Manual
Lime-N-Dah-CocoNut 261 284 Manual
mark221 272 292 Manual
MTAS 258 278 Manual
PACETTR 275 303 Manual
TheMustangSource 266 280 Dynojet Manual

Maybe Ford samples quite few engines and sets the flywheel hp at the point where say 80% of the tested engines are over that number. For example 80% of the ones listed above are higher than 263 rwhp which equals 300 flywheel hp (using 12.2257%)

 

It's much more likely that the engines come underrated than lose less hp than other cars.

 

I think you think too much....

 

It doesn't suprise me much. New technology over the yrs has come a long way.

 

It's more likely that Ford underrates the engine output (99 Cobra fiasco, insurance reasons, etc...) and it's not a good idea to use the advertised engine output as gospel or a baseline.

The TR-3650 is nothing new and has been around since at least 2001 (and much earlier when it was being developed). The 3650 is notorious for being noisy and notchy, definitely not signs of a tight and efficient gearbox.

 

Ok well then why is the Shelby GT rated at 319 and it dynos at 280?

 

It has more horsepower than the standard S197 GT (which we all knew). Seriously, if you're using the advertised horsepower as gospel, then it won't be entirely accurate. I asked Tremec about the drivetrain losses but they only had the figures for just the gearbox (which is what they make for the S197 GT). The driveshaft, rear axles, rear suspension (to a certain extent), differential, gears, clutch, and flywheel play a major role in the final drivetrain losses in a 1:1 ratio.

I recall Doug saying that it was closer to 16% for the S197 GT / TR-3650 combo. I would believe this since the TR-3650 seems like a rather crude gearbox, and the 2-piece driveshaft has a lot of slop. The stock clutch also has its limits.

Using a 16% loss:
269 rwhp = 320 fwhp

Using a 12.2% loss:
269 rwhp = 306 fwhp

This does make the 12.2% loss seem more realistic, but you have to remember that advertised hp figures are sometimes pure fiction. The 2000 Crown Vic dynos 160 rwhp and is advertised to have 215 hp. That's a 25.4% loss! The 98-99 Crown Vics can dyno 180-183 rwhp and are advertised to produce 215 hp. Using the correct drivetrain loss for that vehicle/transmission, it comes to around 210-215 hp (still shy of the advertised figure).

 

That is exactly what I believe. They underrate the numbers to be safe. It goes back to the 1999 Cobras that were to have 320 hp, but had problems. Now they always seem to underrate the hp numbers on their sports cars. The Ford GT has 550... more like 550 to the rear wheels (trust me, its true). The Terminator Cobra's, had 390 hp. Alot of people have told me, when they dyno'ed their cars, it was more like 420 hp at the flywheel. I believe the GT is over 300, but they use this number for a reason.

 

The reason i do not think that we should change to using 12% as a conversion is becasue it won't be able to compare to older cars very easy.

If we use 15% on 280rwhp. converts to 329hp.. and this is what an older car would need to compete with the 319hp mustang. that way it keeps comparisons fair.

so even though the stang only has 319hp its as fast as an older car with 329hp.. so using 15% just makes it much simpler for comparisoons sake.

 

Metro is right about the additional parasitic drag...... and don't forget that includes the wheels too..... I don't know if the stock 17" combo weighs less than the stock 18's, but if there is a noticeable difference in weight this will affect the dyno readings too.