Quote:
Originally Posted by Dwight
Keith Craft once told me that of the engines he dyno-ed and then installed into a Cobra, and then chassis dyno-ed he saw a 20% loss.
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I think on his restoration motors like 428 CJs he probably ran the stock manifolds on the dyno. But on custom built engines KC used tuned headers on his dyno runs - at least going by my experience. So taking a 500 HP engine and installing it in a chassis with 390 log manifolds would probably kill the upper end and could possibly cost 25% at the rear wheels in theory dropping such a motor to below 400 HP.
The day they dyno tested my engine they had three 428 CJ restoration (stock) engines lined up outside the dyno room they had just finished breaking in and running. I asked the dyno operator what they typically made and he said usually stock they pulled about 410 HP. A 428 CJ is not very different from a Q-code 427/400 HP center oiler from the 63 - 64 era other than a bit less bore and bit more stroke and everyone knows by then the 428 CJ was grossly under-rated by Ford at 335 HP. So the 410 HP would seem to compare pretty closely to what Ford rated the 427/400 engine at - but both 427 Q and 428 CJ ran a more efficient exhaust manifold than the 390 log manifolds.
Detroit wasn't messing around with HP ratings too much until the later 60s and their engines in the restoration dyno reports I see in magazines like Car Craft and Muscle Car Review seem to run right on the old manufacturer ratings for the most part. Course that was stripped of accessories and the old rating system.