Horsepower calculation

**Too Fast** · 04-12-2008, 08:51 AM

Here is a formula to get a close idea for your cars' HP if you have not had it to the dyno yet (or have other things to spend your $$$ for):

HP = (MPH/234)3 x weight (MPH is your 1/4 trap speed)

For me I put these numbers in:

HP = (109.89 x 234)3 x 3675 (I don't know how much my Trans Am wieighs, I am guessing 3500 plus my 175)

HP = (0.4696xxx)3 x 3675

HP = .1035581 x 3675

HP = 380.57601

I don't know if this is flywheel HP for sure, but my guess is it is. If I multiply 381 x 88% (I think you have about a 12% drivetrain loss for M6 cars) I get 335, which is about what I see for other cars like mine, long tube headers, lid, ORY, muffler change.

That trap was last October, last May I had a trap best of 107.5. When I plugged in that trap speed I got 346 HP (305 with 12% drivetrain loss). I did no tuning between these days at the drag strip, I think the weather was 20 degrees cooler last October. Interesting to see this calculation shows ~30 HP difference for a little over 2.3 MPH trap speed change.

**wildbanshee** · 05-06-2008, 07:02 PM

i was looking at that same formula online...there is another one for et...which is different.
i ran a 13.5 @ 106. the formula you first gave suggested 343 hp and the et suggested 297hp. i have the free mods and an ud pulley..accurate??

**Too Fast** · 05-07-2008, 01:22 PM

Sounds accurate. Maybe the one you found is for RWHP? Can you post the formula? But ET is highly variable, all depending on your 60 ft traction. If I were brave and used slicks with my stock differential, I bet I could get some 1.7x 60 foot times. On my 12.89 @ 109.89, my 60 foot time was a 2.01, that would drop my ET by .2x-.3x I'm sure. Last October my MPH were all over 109, my 60 foot times were from 2.01-2.31 with ETs up to 13.3x

**wildbanshee** · 05-14-2008, 05:48 PM

the formula is at http://www.musclecardrive.com/calcul...calculator.php
12.89 is what im really shooting for as i worked the formula backward using the 343 number and the weight of the car and it pointed to 12.89 et....figure that s a reasonable target. you are at that time with only long tubes? did it do that much? i have the free mods and a pulley...oh and the 10hp from royal purple..the jury still out on that one. i used to race in the late 80's...12's were/are wicked fast im still in awe of these cars!

**wildbanshee** · 05-14-2008, 05:50 PM

im only guessing its for RWHP ...seems strange to put the 20% reduction in the foumula?

**Too Fast** · 05-15-2008, 03:01 AM

I agree it seems to be for RWHP on the ET equation. I did their calculator both ways and it came out as what I said in my first post. Using their calculator sure is easier!

Before my Hookers and ORY (I have a lid also) I was running 13.3x-13.5x @ 104.5-105.x. My ultimate goal for the car is to run 12.99 @ over 110 MPH on my slow nights (hot weather). I think I can do that with a LS6 intake and a tune.

I raced in the late 80s as well with a '67 400 4-speed Firebird, its' best times were 13.2-13.4 @ 104 -105.7. No slicks. Yeah, 12s are very fast. That old car got 8 MPG city/10 on the highway. New car gets 16 or so and 25-28 on the highway. And doesn't overheat. And stops more than once, with antilock. My '67 handled pretty good due to massive front and rear sway bars and modern rubber.

**blackbirdbrain89** · 05-17-2008, 09:48 PM

i dynoed my car @ 341HP AND 351LBS OF tq to the wheels and i ran a 12.9 @ 110 with a 2.0 60 ft im thinking next time i take it out ill get a 12.8 and a 1.9 60 ft