When on a dyno that gives rwhp how much loss can you figure thru the drivetrain for an automatic? I've heard as much as 30%

 

[quote author=moneyman link=board=7;threadid=20003;start=0#msg188134 date=1064330448]
When on a dyno that gives rwhp how much loss can you figure thru the drivetrain for an automatic? I've heard as much as 30%
[/quote]

30% too high. The "standard" practice is 20%. I'd put it closer to 15 to 17% personally.

 

Interesting. Now turn that around. How much power loss with a standard?

 

Nominally 15% for standard transmission drive trains. This accounts for rear diff and some frictional losses through the transmission, though you should be in direct 1-1 for the dyno run.

Automatics can be over 20% depending on torque converter size/health, clutch health and internal pump pressure. Having an automatic near 15% would probably be in race trim with a huge locking TC and high clutch force. IMHO :

J-eh

 

[quote author=Lil Dog link=board=7;threadid=20003;start=0#msg188234 date=1064345390]
Automatics can be over 20% depending on torque converter size/health, clutch health and internal pump pressure. Having an automatic near 15% would probably be in race trim with a huge locking TC and high clutch force. IMHO [/quote]

I'd have to look for the old sheets, but it was with no convertor lockup. I wanna say it was 16% on my truck when I tested it, if I can find the old dyno sheets I'll verify.

 

~20% with an auto and ~15% with a stick. Both of them could vary due to the holding ability of the TC/Clutch. A truck with a race built auto (ATS, DTT, Suncoast, ETC...) would probably be closer to 15% than say a stock transmission which could vary from 20%-30%. The only thing that would affect the standard would be the clamping force of the clutch.

 

How can you test the losses on the dyno?? Do they measure slippage somehow??

You would have to have a tach read out on the engine and the output shaft of the tranny, as well as knowing the absolute final drive ratio out of the tranny to calculate for loss/slippage.

If you calculate roll slippage, then thats another set of variables for the dyno..

I would be interested in this...

J-eh

 

Here's an easy way. My engine stock dynos 235 hp at the flywheel. Account for a 20% loss through the drive train and you should come up with ~180 rear wheel hp. Now, I haven't had my truck on the dyno, but I bet alot of people with a stock truck have and I'm almost willing to bet my bottom dollar that they dynoed around 180 hp. This is with an auto.

 

How do you dyno an engine in the vehicle? Just the engine, no drivetrain.

 

[quote author=BigBlue link=board=7;threadid=20003;start=0#msg188310 date=1064358261]
Here's an easy way. My engine stock dynos 235 hp at the flywheel. Account for a 20% loss through the drive train and you should come up with ~180 rear wheel hp. Now, I haven't had my truck on the dyno, but I bet alot of people with a stock truck have and I'm almost willing to bet my bottom dollar that they dynoed around 180 hp. This is with an auto.
[/quote]

First time I dynoed my stock truck I got 205.
2nd time, same truck, still stock, I got 187.

Only difference was the Dyno.
One was a Mustang, the other was the other brand but I'm not sure which was which.
2nd time was on Edges dyno, whichever model that is.
(getting old and forgetful)

Both times they had trouble keeping my TC locked up.


phox

 

There's a way they can come quite close at measuring loss. I recall it was a coast down scenario. Most folks just do the 15 and 20% fudge factor.