Chassis Dyno??????

[art leong]

Wondering about those ET predictors? Are they calibrated for drive wheel horsepower or flywheel horsepower? Is there a way to calculte one from the other?
I'm using an automatic and have made 210 hp (so far) on a dynojet chassis dyno.
Trying to figure how far off the mark I am.
Thanks
Artie

[SSDiv6]

Originally Posted by art leong

Wondering about those ET predictors? Are they calibrated for drive wheel horsepower or flywheel horsepower? Is there a way to calculte one from the other?
I'm using an automatic and have made 210 hp (so far) on a dynojet chassis dyno.
Trying to figure how far off the mark I am.
Thanks
Artie

Most of the available ET predictors calculate "Gross' horsepower" based on SAE J245; this means, it does not account for any accessories. Other available higher cost predicting programs, are more accurate and account for accessories and other factors, which would give you "Net' horsepower in lieu of "Gross" horsepower. As a general rule, the "Net" horsepower reading tends to be approximately 80% of the value of the "Gross" reading.

Dynos measure horsepower under the conditions of the day, then apply a mathematical conversion based on SAE J1349. Predictions programs are a hit/miss in regards the numbers you get since there are too many variables. Also, dyno numbers vary between brands, the way they are used and the setup. I have seen dyno numbers vary as much as 20+ horsepower on the same engine between brands. Also, the rate of the pull and the operator can change the numbers too. Most of the prediction programs do not come close to the actual real numbers.

My recommendations have always been to run your engine on the dyno for a baseline, install the engine in the car as if ready to race, and then run the car in a chassis dyno. You will be surprised how much power you can find in a chassis dyno.

[Ed Wright]

I agree. I have a Dynojet, and think that et prediction/1/4 mile run simulator deal is a joke. I never use it. How fast you can spin up those rollers has very little to do with how quick the car will be. I tune a lot ot cars making 100 more rwhp than my car at about the same weight, yet run over one second slower. Way too many variables. Its good to know, however, where you are at the track versus how much power your making at a given time. After a while you will have a somewhat fair idea how much your car will pick up after seeing gains on the dyno. It's a handy tool to have access to.

[n2oracer]

What kind of affect does the converter have on a chassis dyno? Can you get any kind of meaningful results with a loose (5500+) converter?