Has anyone ever taken their motor out of their car and put it on an engine dyno AND THEN put their vehicle on a chassis dyno to determine the ACTUAL drivetrain losses for their car? I have seen estimates ranging from 13% to 24% depending on who does the estimate and that range seems like a huge difference to me. Granted, I would NEVER be able to afford something like that, it would just be interesting to see.

 

I never have because there's just too much work involved in order to see what the ACTUAL drivetrain loss is, but for our Montes the general rule of thumg is 20-25% drivetrain loss.

 

There has been at least 1 or 2 run them on an engine dyno over at clubgp, but it was quite a while back that I remember reading about it. Not sure if they ever went to a chassis dyno to compare numbers.

One problem with that is- among all the other variables (ie testing at a different location/day/etc), which chassis dyno do you compare it to? A mustang and dynojet put out different numbers even between the two.

I will say 13% is definitely way too low on these cars. One easy way to roughly compare is to look at what people dyno with stock cars. There have been plenty of people dyno with stock L36's and L67's (more comparable back when these cars were much newer)- and assuming GM's engine power numbers were correct (I don't see why they'd have any reason to fudge numbers up or down on regular passenger cars)- then the 20ish% zipper mentioned is as close as you're going to get.

The other thing is- bhp doesn't really mean a whole lot in the aftermarket world anyways, at least not in modern cars. The only people I hear brag about crank numbers anymore are old school muscle car guys. With all the chassis dyno places out there- no people with modern cars really care what the crank hp is anyways, because what you put to the wheels is all that actually matters. I always laugh a little when I hear some of those old school muscle car guys bragging about their 400, 500 hp big block- then you figure minus that big turbo 400, minus the steel driveshaft, minus the big rear end, minus the massively wide tires- actual whp on some of those old cars can be pretty weak.

 

I too, am confused as to why one would want that...I mean you really can't run the motor down a track without a car, so what would the point be of measuring crank hp? To the wheels is really the only one that matters unless I'm missing something?

Joe

 

Why dyno an engine? Simple. Torque & HP curves. These curves DETERMINE when you shift in the RPM band. Modding a transmission is just as important as modding an engine. For example: shift times- Ferrari, Porsche & Lamborghini spend 10's of millions a piece, each year to bring those shift times down a few milliseconds (and all automatics). Clutch slippage- Did you know that GM designed the 4T65E to ALLOW slippage if TOO MUCH TORQUE is applied? This extends the life of the transmission internals & prevents GM from having to replace it. I usually hang at ClubGP and it has been tested on a dyno that 17.5% is the HP loss thru a GM 4T65E. Example: GM lists the NA 3800 Series II at 200hp, however when measured in stock form on the dyno, the WHP is 165. Ergo 200chp x 17.5%trans loss = 35lost hp...and so 200chp - 35loss hp = 165whp. Several cars have been Dyno'd and 17.5% is a consistent & accepted number. P.S. on the street your slicks and track times mean !@#$.

 

Since when can't you can't get HP and Torque curves from a chassis dyno?

IMO, that's too specific a number- especially considering a mustang and dynojet dyno both put down different numbers. Add to that the wheel/tire package someone is running can make a big difference too.

As was said above, it doesn't really matter what the crank hp is anyways- all that matters is how much is getting to the wheels. We don't have any drop in other transmission or rear end options like most RWD cars have, so we're all stuck with roughly the same drivetrain loss anyways- there is not much we can do to drastically change that number running the same trans.

If you're curious what an approximation of your crank hp is, ballpark 20% loss and be done with it.

 

I agree with bumpin, 17.5% is WAY to specific. Like bumpin mentioned, there are too many variables. I've seen a Monte with a 3800 dyno 145whp, and I've seen a number of 3800's dyno in the 150whp range. Even the Corvette ZR1 was dynoed at 505whp (I believe it was Motor Trend that did this particular test). That's 21% drivetrain loss in a Vette.

But who cares? The only numbers that matter are whp and wheel torque numbers. I will agree though that if you're into street racing, your track times mean nothing.