Flywheel HP vs. Rearwheel HP

[Erv M.]

In 1972 chevrolet converted to RWHP versus FWHP. With the introduction of less compression and with the hp rating changed the numbers really dipped. What true hp did they lose in the base 350/300 with a RWHP of 200?

Is there a standard HP loss per component to the rear wheels you can apply?

I have a base 1969 350/300 automatic with 3:08 rerend, what do you think the RWHP rating would be?

[Dennis S.]

Re: Flywheel HP vs. Rearwheel HP

In 1972 chevrolet converted to RWHP versus FWHP

I thought those were "as installed" or "net" SAE ratings, not RWHP from a chassis dyno.

[Duke W.]

Re: Flywheel HP vs. Rearwheel HP

The conversion you refer to was SAE gross to SAE net at the flywheel. OEMs have NEVER quoted RWHP.

See the Fall 2010 Corvette Restorer. I explained all the different kinds of "horsepower" along with empirically derived conversion factors for SBs with full dual exhaust systems.

The only way to know what your engine puts out is to test it on a Dynojet chassis dyno. Then you can use the conversion factors to compute (approximately) SAE net and gross at the flywheel.

It's also a good way to check if you fuel map is optimized, and allows some ignition map optimization. Typically dyno operators charge about $100-150 for an hour. Do some road testing, know your baseline, put together a test plan, and have some alternate distributor springs, and you can not only learn a lot, but you can usually find some improvements that are worth the cost of the hour of time. Again, see the above referenced Restorer article to see how to do it.

Duke