It all depends on the transmission (ie TKO600, tr3650, tr6060) as they have different components that would factor into effeciency differently. The cars driveline components will also factor in (ie 2 piece driveshaft vs 1-piece, weight of components, flywheel size, etc)

when people say 15% loss for manual or whatever, that is a generalized statment. I typically here 15% for a manual and 18% for an auto, but that needs to be taken with a grain of salt since they are general statements. Yes, dynos can show variance, the dyno operater has to input parameters which may differ from another dyno operater's input (ie car weight, etc).

 

General rule of thumb I have always used was 15% loss manual, 20% loss auto.

Is that perfect? heck no its a ballpark. If you really want to know remove your engine and put it on an engine dyno as that is the only "real" was to gauge crank HP.

I also use the "guestimate" formula above to go from RWHP to CHP.

484rwhp x 1.15 = 556.6 chp

Is what it is.

 

It boils down to, no 2 cars are alike, 2 different 300 hp Mustangs same year same options will not dyno the same numbers

 

actually, you would take rwhp and divide it by .85;
multiplying rwhp by 1.15 is incorrect because you are only adding 15% of 484, which is a smaller amount than subtracting 15% of the crank HP. (15% of 484 < 15% of a number bigger than 484 which is CHP)

484 rwhp/.85 = 569 chp
569 chp x .85 = 484;

557 chp x .85 = 473.5 rwhp

 

BTW, 300 crank HP bone stock is a minimum value that Ford EXPECTS from our GT's. I suspect the vast majority of our Stangs come off the line higher than that, hence the guys that are seeing bone stock dyno numbers in the 270 RWHP and higher range. There are those that have dyno'd in the 255-260 range. Factor in the dyno's tolerances and other variances and you can see why we're all over the board.

There is no magical formula. Just "typical" values where the percentages tossed around above are a decent guideline.

 

I've heard that overtime cars lose hp, but i wasn't sure how many years/miles it would take for that to happen. i'm going to have my gt dynoed soon, its an 06 with 39700 miles. should my numbers be about the same as when the car rolled off the line when it was new, or will the numbers decrease?

best regards,

ben

 

People who dyno at 270 hp stock, that number is very consistent within the range of the sorts of calibration errors that you find on those machines, or the sorts of cars you get that are above average once in a while. There's a lot of variation in the process if you educate yourself about it.

There was an article where a magazine though that dynoed a stock GT500 a GT & a Shelby GT on a calibrated dyno and found the drivetrain loss to be about 15% in every single case. This number is also consistent with engine builders for the Mustang that have engine dynoed the 4.6 as a baseline and then put it into a Tremec 6060 equipped GT resulting in a measured 15% drivetrain loss. With various manual transmissions it seems to be a consistent number pegged there.

 

that is the number I go by and 18% for AUTO
I had 270 RWHP with CAI and tune. Now 465 RWHP so that equals
465/.85=547 crank HP