Dyno numbers

[TIGER 6]

Not sure if this is the correct location for my question. In any case, my question is this:
I have a 2004 Daytona with a 402R engine. Roush "guarantees" the engine will produce 515hp and 500lb./ft. of torque.Understanding that there will be hp and torque losses at the rear wheels due to drive train,exhaust etc., what should I expect will be the dyno reading for this car and engine at the rear wheels? Thanks for youe opinions.

[Ibr8k4vetts]

I have read any where form 10% to 20%. Hope this helps,
Mike

[blykins]

Or more...IRS will take up a little more....My guess would be 15-25%. My '02 Stang GT (260hp rated) dyno'd at 228.....so that's a 13% loss....I would consider that on the "good" side of losses.

[Bill Wells]

so many variables can cause different losses. side pipes on a roadster alone can eat 50 hp in many cases. no idea what similar losses might be experienced on what appears to be a more complicated under car exhaust system on the spf coupe. more or less ? dunno. an engine on a dyno stand under ideal conditions with a different carb than when tested on a chassis dyno can alter results too...as would ambient temps, humidity differences as well as carb jetting/ timing etc on one dyno vs another. mustang brand chassis dynos usually give lower numbers than a dynojet brand chassis dyno based on experience of some of my friends. typical parasitic loss numbers i have been quoted from engine dyno to chassis dyno would be 17-21% loss differential. some higher, some less. use the chassis dyno as a tuning device and forget the numbers, rather look for directional changes from one xyz adjustment to another, ie, did the change directionally improve or hurt vs the baseline pulls. doesnt roush provide dyno sheets for each specific engine ? if so, you can calculate your own parasitic loss numbers comparing chassis dyno results. i use chassis dyno for tuning purposes, they are usually humbling and perhaps meaningless except for tuning efficiencies. if you have a roush engine dyno sheet , tell us your experience after a chassis dyno tuning session and see if it varies considerably from a 17-21 % range. bill.

[Tim Brewer]

Find you a chassis dyno and then you'll know for yourself. But don't beat yourself up when the numbers fall a little shorter than you expected them to be. Like Bill says, use the dyno to tune and don't worry about the HP #'s so much.
Tim

[TIGER 6]

Thanks for your replies.Bill,I have some data and would like your and others opinion.The data sheet Roush sent with the motor shows 497.9 C Pwr C_Hp at 6000 rpm and 435 CTorq C_FtLb at the same rpm. The engine redline is 6500 rpm so I would assume that the Roush advertised 515 hp is correct. I am not so sure,however,about the 500 lbft torque number. I had the car dynoed several months after purchase on a dynojet.
We did 3 pulls with the following hp/torque results:378.03/389.6, 382/393.01, 385.43/393.34.





































As the car did not have rev limiter at the time{does now}, I was shutting it off at ~6300-6400rpm.If I take a 20% reduction in the hp numbers, I should be pulling around 412hp at the rear wheels and 400 lbft of torque. A 15% reduction should result in 437.75hp and 425lbft of torque.
Any thoughts?

[marcocsx3121]

Your chassis dyno numbers are definitely lower than I would expect based on the engine dyno sheet. As an earlier post correctly indicated, there are a number of variables that can have a fairly dramatic effect on rear wheel horsepower.

As an aside, I drove the twin of your car (Brock coupe, 408 Roush) a couple of months ago, and based on my seat of the pants dyno, I'd say that mid to high 300s at the wheels felt about right.

[Bill Wells]

if you take your numbers and use a 20% loss number at rear wheels, your calculated crank hp would be 473, 477 and 481. torque numbers would est to be 486, 491 and 481 ft lbs.

those numbers are not so far off of the advertised 515 hp and 500 trq, but your loss would be 26%on hp and 22% on trq.

not sure that is worth getting upset over as there are still so many other variables in a chassis dyno real world setting vs a clinical perfect condition engine test stand dyno. chances are the engine numbers at that time are correct and there are additional parasitic losses , or different other variable conditions attributing to the lower than anticiapted rear wheel numbers.

as i said before, to most, chassis dyno numbers are humbling and less than expected based on 'supposed' engine crank numbers. the truth is in the tuning aspect and some sort of reasonable explanations for losses.

in a perfect world, your rear wheel numbers at a 20% loss would be expected to come in at 412 hp vs your average of 382 and trq numbers at 400 vs your average of 389.

other thought is : engine or advertised numbers are NOT as high as advertised. short of an actual engine dyno for your specific engine you can only use the adv figures. some engines most likely produce more than adv and some less . just like some new car mfr's found out not too many years ago. their customers started complaining on low chassis dyno numbers and the mfrs said 'gee, guess what..we just retested and found out our hp numbers are indeed LESS than we advertised...mazda for one as i recall and ford svt mustang for another. i recall some vipers perhaps in that same situation too based on some local viper owners here whose club rented a chassis dyno shop for a day of bragging rights / comparisons and one owner had his engine replaced due to low chassis dyno numbers. however, another put his car on the dyno at the viper plant and got a whole different set of hp/trq numbers, higher than the local shop. whose was right ? hmmmm....ya never know.

so, as bill clinton said : what is the definition of IS ? IS it as advertised or not ? or is it ok and your losses for some reason specific to your car or similar cars showing higher % losses than what is norm. then the debate of what is NORM ? this is a snowball in hell or a snowball rolling down the hill..does it melt or get bigger ? you will never know unless you yank your engine for test stand dyno (unlikely)< live with the numbers ( they aint shabby) and/ or solicit similar input from other owners of same car with same engine /driveline/ ratios and see what they experience. then a new variable starts... what is the real world accuracy between dynojet A and dynojet B three states away.

me, i would live with it. accept the chassis dyno numbers for tuning purposes and go out and enjoy driving one of the finest cars on the market that can kick 98% of all other cars butts, regardless of what an estimated or calculated hp is...

my $ .02 worth, and wish i had a coupe, no matter the engine. b