I've been playing around with Desktop Dyno, but the program only supplies power estimates from the flywheel. Is there some sort of calculation that I can perform to compensate for driveline loss in my car?

 

I've read that;

Manuals usually lose 15%

Auto's usually lose 20%

I've heard varying estimates from 17% to 24% for auto's and again different opinions on manuals as well.

So, take it with a grain of salt.

Flywheel HP * (expected loss in decimal form (20% loss = .80)) = Estmated RWHP

 

I've always figured around 12% for a manual and 15% minimum for an automatic- significantly higher if it's got a high-stall converter.

My Mailibu lays 390 to the rollers through an automatic trans with stock coverter. Add 15% driveline loss and that's about 450 at the flywheel. That's what I built the motor to make so the numbers pass a basic sanity test.

 

Thanks for the numbers, guys. I'm just trying to compensate for everything in the somewhat-innacurate Desktop Dyno. 275 hp on a 9.0:1 motor with 882 heads... . Oh well. I guess I'm supposed to look for change, versus absolute statistics.

 

I really have no clue how you gained 150hp at the flywheel due to a tranny and stall

sorry but your math comes out to a 33.333 percent loss


also another thing to think about drivetrain loss can never be a exact thing

rpms spun, wieght,oil thickness and type, tires, rims, how the gears are cut, and many other factors make a difference as to how much you lose through your car before it hits the wheels


and another thing to me percentage of loss is kinda a stupid idea


lets say you take a full drivetrain from a v8 making 500hp at the crank
take 15% from that and you have a loss of 75hp

now take that whole drivetrain from that car and put it behind a v6 making 145hp and it only has a loss of 21.75hp

something seem wrong with this?

 

Where did you come up with 150?

 

Ive found that when playing with DD2000, it is more realistic to put on "HP manifolds and mufflers" when you are using headers. It simply adds way too much when you use "small tube headers"

Do you have the actuall flow numbers on the 882 heads in there? or are you using one of their generic heads?

 

I took the flow numbers out of Chevy Hi-performance's article and got the actaul flow numbers for the more popular sets..

Edit: forgot pic, my bad

 

.

 

you're right.. thoes numbers are way too high for thoes heads.


i hate thoes heads. i had a bad experiance.

if i ever have a friend that has thoes.. im going to crack them... that way, he HAS to get new heads.... he might hate me for awhile, but he'll thank me later.





right now desktop dyno is showing me around 500hp for the motor im building.... i think thats wayy high... i really wonder about the accuracy of the head files i find online....

right now i have 3 head files for my Dart Iron Eagle heads.... all 3 are pretty diffrent.

 

I'm using DD's included 882 head file. Those numbers coincide with numbers that I've seen from other sources, too.

I don't actually intend on building a motor with these heads (though, my 882 heads are the better version), but I wanted to see roughly how much power this 350 I have will produce. I set up the DD file for an L48, which is what I have -- motor from a 1974 Corvette, 195 hp. Desktop Dyno said that it puts out 250 hp... which is why I thought about driveline loss. But, I guess that GM always quotes raw engine power, not rear-wheel power. The discrepancies lie with the computer, I think.

Anyway, no need to have a "Desktop Dyno inaccuracies" thread -- I've read all of those already . Just checking on driveline loss.

 

I have found that if you deduct 10% from the DD2000 numbers it comes much closer.

 

well just noticed I was a tard and missread

thought he said 300
not 390
oops

 

There are some excellent discussions of drive train loss, rotational inertia, chassis dynos, etc. in the tech notes here:

http://www.pumaracing.co.uk/mainmenu.htm