Drivetrain Loss Help

[LS1GN]

I'm trying to figure out my horsepower using my trap speed. Most of the calculators are giving me 335 horse or so. I am assuming this is power at the rear wheels. So now I am wondering what is the power at the crank?

Also is this 335 AVERAGE power for the run, or max power?

Does anyone have any pertinent info on driveline losses, especially with an automatic trans (700)? I know the diff takes power and the driveshaft too, but I am guessing that the lion's share of the power loss is heat in the transmission, right?

I have googled this and some sites suggest 18%

What do you think?

PS - here is my data: race weight (with me) 3460 trap speed 107 ET 12.8

 

[GhettoRacingKid]

im sure you can find something on here

http://www.wallaceracing.com/Calculators.htm

 

[CHRIS.O]

I calculated about 16 percent loss on the dyno last time I was on one. 4l60e transmission.

 

[LS1GN]

Thanks guys.

That Wallace racing site had some cool calculators, I am closer to 350 horse (I think that is at the crank) and the calculators are saying my car should be a HALF SECOND ahead of where I am at 330 feet - meaning I am making more power at the big end and really stinking it up down low.

Are the numbers given average horsepower required for a run or max numbers?

 

[CHRIS.O]

One thing I don't believe the calculators will take into account is wheel spin. Are you hooking the whole way? Obviously a little wheel spin at the low end will make your top end look better.

 

[LS1GN]

I've read that... but the wheel spin doesn't actually give you MPH. Whellspin simply masks or disguises a better ET that you don't have because of the wheelspin. Right? A person's trap speed will be about the same (within 1 mph or so) regardless of the launch. Right?

I have old, hard Nitto DR 245/50/16s. I know they spin in first, but it is hard to tell how long they spin and not sure if they spin at the shift into 2nd. It is an old 100% stock transmission so it is the polar opposite of crisp,hard shifting.

 

[dogsht]

Thats why some people paint a stripe on their tire so that they can watch it in slo mo to see if they are spinning. The other thing to remember about the calculators is that they have to assume optimum gearing which is usually not the case. But you can use actual weight & HP etc to determine optimum gearing. For example my target build was for 500HP with peak HP at about 5,000 rpms. The calculators said 500HP could take my race weight to 115mph in the quarter. So I geared my car & tire height so I would hit the stripe in third as close to 5000 rpms as possible.

 

[CUTLASSJESSE]

your most likely spinning all the way through first but with the trans being stock and assuming no shift kit and the ratio difference from first to second its probably not spinning in second

 

[LS1GN]

Jesse - Yes, duh, I should have known that. The 700R has an ultra low first gear and then a big jump in ratio to second.

Dog-I'm still learning this stuff - yes - some guys gear/tire a car for ET which sometimes is a slower MPH

 

[dogsht]

Optimum gearing should not only give the best et it should provide the highest speed thru the traps for the power & weight of your car.