Horsepower question...

[Vaman]

Does anyone know how to roughly estimate the flywheel HP if you know the wheel HP? I'm sure it varies quite a bit depending on drivetrain configurations. Thanks in advance.

 

[BCFAST]

For a manual gearbox truck, figure between 15-18% loss thru the drive-train... an automatic, far worse.

 

[Rammin On]

A rule of thumb generally used is around 20% loss ... so if your RWHP is 288 here is the formula:



288 X 100

________ = 360



80





Hope this helps ... . if you know the actual driveline loss ... then calculate respectively . .



Keith

 

[Dennis Garrett]

Wondering about that myself, I conservatively estimated 10% with an auto in lockup, but it might be worse than that, certainly more than that out of lockup. On the dyno, locked up, mine showed 278 HP (& 649 torque) at the roller, at about 31 psi boost. Somewhere in an old TDR back issue, it was estimated each 1 lb. of boost would be roughly 10 hp. If this the case, I'm making 310 HP (At the flywheel?) and putting 278 down to the roller. Believe it or not, this is a stock, original truck with 140,000 miles, and the entry level 230HP/605 Ft. lb. plate moved 1/16" forward. If I estimate correctly, this equates to about an 11. 5% loss through my locked up transmission.

 

[BCFAST]

DG, I think your estimate is a little optimistic. The BEST an auto in lockup could hope for would be 22% or worse... perhaps Mr. Kondolay could jump in on the automatic issue. In our race cars with a transaxle and half-shafts, we calc a 15% loss with synthetic lube and competition-assembled gearbox. A set-up like our trucks' would be closer to 20% if everything was 'just right' in the 5 speed and drive train.

 

[Dennis Garrett]

OK, lets do it this way. If two runs on the dyno came up with 278 HP, & 649 torque to the ground, at 2200 RPM, & 31 psi boost, in lock up "D" , then add the 22% loss to that, it comes up to 339 HP. How can that be with the 230 HP TST plate? The injectors, pump & everything else are original except for the plate & orfice. I've had the truck since it was new. I'm not a mathmatition, hell I can't even spell it, but 339 seems a little steep for a 180 hp engine. .

 

[Ray Torresdal]

dyno

It isn't impossible that dynos will vary! When was the last time the dyno was calibrated, etc. , etc. I'm not trying to rain on anyone's parade, but not all dynos are created equal, and they need maintenance just like our trucks. I saw 20 Hp. difference on 2 dyno's and havn't a clue which one is right - nor does it matter. I've got a baseline for myself, but wouldn't bet a beer on it unless we were comparing hp. on the same dyno, on the same day. Ray