Some one knows?

[Squa10]

hi, so does some one knows how does the rwhp formula works? i mean you have blahp engine and bla tranny, bla rear end, and add all and then you divided by infinitum and thats your rwhp (the blathing is just some kind of example)

[stonebreaker]

It's more a rule of thumb than anything. For an automatic transmission, add 25% to your rear wheel horsepower to calculate engine horsepower.



For example, my impala club dynoed 3 completely bone stock carsduring a dyno day. All of them were rated from the factory at 260 hp. We saw 206, 208, and 210 rwhp on these cars. 208 * 1.25 = 260.



Now that I've seriously hopped up my engine, I really don't know if that rule of thumb holds true. In reality, the transmission absorbs x amount of torque while accelerating. To get a truly accurate picture of how much torque is absorbed, you'd need to know the rotational inertia of the system (from the crank to the wheels) plus the efficiency of the converter and diff. To me it's just easier to use the rule of thumb.

[Squa10]

so if you have a 500 hp engine you have 375 hps on the rwhp more or less??

[jusbo]

The link below should help you out some. If you want a weight estimate there was a thread brought up about a week ago about weight....you'll see what I mean when you get there.



http://www.rpmoutlet.com/dyno.htm

[wheelspin]

I was at the dyno with a buddy on friday night his car had 543 rwhp after all was said and done the machine shop doing the dyno said that it would equate to about 675 flywheel hp and its a 5 speed. scary thing is its only a 302( the its blue oval powered)

[jusbo]

http://www.s10v8.com/images/smilies/icon_eek.gif

[stonebreaker]

On 2007-10-21 14:18, Squa10 wrote:

so if you have a 500 hp engine you have 375 hps on the rwhp more or less??

No, 500 at the crank would equate to 400 at the rear wheels. (400 * 1.25 = 500) But don't get hung up on big numbers. Use the dyno as a means of documenting a RELATIVE change in your horsepower so you have some idea of what the car should do on the track. A given horsepower number really doesn't mean crap - it's like a sprinter bragging about how much he can squat.



<font size=1>[ This message was edited by: stonebreaker on 2007-10-23 15:35 ]</font>

[wheelspin]

well your formula is pretty damn close to what the dyno owner figure for my buddies car tha is a drop of 132 hp from flywheel to rear wheels. this is a very well known engine/hotrod shop in my area very relibale man in our area who we have known for years so Ill stick with what he says.