I got one of the early sets way back when and they replaced my lightly ported 906 heads with big valves that flowed about 255-260cfm. There was an improvement for sure, but because of a camshaft change at the same time, I can't contribute it all to the heads. I had absolutely no issues with the heads at all, they worked well.

With a decent sized street/strip camshaft, flat top pistons, the E heads, 1 7/8" headers, single plane intake and a 750 carb it made 360rwhp (about 450hp) on the dyno-jet chassis dyno and ran high 11s at 115mph in a 3600lb B body with 3.91 gears.

-Dan