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Originally Posted by Anthony
Obviously, your 25% loss is not only drivelline loss, but also loss do to the exhaust system, and maybe even the air cleaner as well, so it maybe it's appropriate. In addition, from your post, it appeared that the chassis dyno was not the same guy who built/dyno'd the engine on the stand, which may also enter some fudge factors in determining % hp loss.
Like you said, I think to get optimum performance, you need to have it chassis dyno'd and TUNED, as there can be large performance gains with the engine set-up right. It beats taking the car the strip, and repeatedly drag racing it, adjusting things to try to determine the best state of tune. Probably easier on the car as well.
By the way, I guess you're running a sbc? What is it's displacement ?
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It's a Rodeck 404 cid alloy block with Victor Jr. heads, manifold, and Street Demon carb.
You're absolutely right as far as the different dynos. Both were Dynojets, but other than that everything was different. The engine dyno was in Wisconsin and the chassis dyno was at Keith Craft's Plano shop. I have heard that the Craft dyno tends to be conservative, but have no idea if that's true. I do know that, when Rob dynoed it, I had him remove the sidepipes and check the hp difference. Even with rejetting I think it only picked up 10 hp or so, so I think my pipes are pretty efficient. The air cleaner is a pretty large K & N with a K & N lid, so I think it's pretty efficient, too. I'm running
synthetic fluids in the tranny and diff, so I feel I've minimized frictional losses there. It has a bimetal 'Vette flywheel so it shouldn't be losing much there.
I guess the conclusions I draw are that either the builder's dyno was very optimistic or the chassis dyno was very pessimistic. The Corvette tuners all use a 15% loss factor and it seems to be accurate; given that my diff is Corvette I would think it would be similar for me. Maybe the M-22 Cal Metal built for me is still tight and needs some breaking in (1000 miles on drivetrain).
Whatever the case, as I said I think you should use a dyno as a tuning device, not worry about the numbers so much, and judge the car by how it gets down the road.