Your numbers are right on par for what you have. People have a very big misconception of what their car will make on a chassis dyno. The two biggest factors for being dissapointed are:
- Being told the motor makes XXX hp on an engine dyno, and
- Not knowing the reality of drivetrain loss
I have guys coming in all the time with "500hp" motors, and they expect big numbers at the wheels. The fact is, their motors don't really make the power they think they do, and then their engine builder usually has no clue of real drivetrain loss.
Something else to factor in, is even if your motor DID make say, 500 hp on an engine dyno, that's with real long tube headers usually. Cobra sidepipes cost a good amount of power. Case in point... Had a Cobra here yesterday, with a built 428. Customer was told the motor should make about 475hp. First pull, car made 297 at the wheels. Now, his A/F was very rich, and I told him he'd pick up some power if we adjust the jetting. Of course, he wasn't going to get 100hp from jetting, but that's where you start. When I went to put the probe in the tailpipe, I couldn't get it into the muffler part of the pipe, and found that odd. I also noticed that his car was much quieter than any other Cobra I've dynoed. Upon further inspection with a mirror and flashlight, we found that his side pipe design was SUPER restrictive. He had 4 two inch primaries going into a 3.5" muffler, with whatever inside it, and on the exit side, there was a big baffle plate with a small 2" pipe sticking out of it. So basically, 4 x 2" in, single 2" out. Not good for power. So let's factor all this in.... 475 hp - 15% drivetrain loss for his toploader and Jag rear give you 403rwhp. I estimated he was losing about 70hp through his side pipes. That's 330rwhp. I guessed that he may pick up about 30 hp in jetting, from his 297. We changed the jets a few times, and what do you know, 330rwhp
.
The funny thing is, I've had a lot of FE powered Cobras on my dyno. Not ONE of them has broken the 400rwhp mark. The ONLY Cobra's I've had break the 400hp mark were two stroked 351 cars (a 392 and a 406).
So given all your info, I would say you are right on the money.
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