HELP! Poor engine power

i have a rebuilt 1976 302, Windsor jr heads, Edelbrock 7122 high lift cam (0.496" lift and 290 /224 @.050 lift) with a holley 600 vac sec, Ford Cobra 9424a? manifold, Standard flat top pistons and rings and crank and headers. The engine used to have Standard heads, an edelbrock Torker 2 and a similar spec Crane 280 cam, it ran brilliant with lots of torque. I then fitted the new Windsor Jr heads (complete with valves etc. fitted). My Engine builder rebuilt the engine with the diffent cam and manifold. He couldnt get the old manifold to seal so he fitted this ford Cobra unit as it was the only one of 5 in his workshop that he could get to seal the water passages properley. It was proffesionally set up on a dyno by a well respected tuner. However now the engine runs very sweet and quiet but the power is useless. The dyno showed only 245 hp at 5,000 rpm with 270 lb's ft torque at 4,200. The only real change was the manifold which looks more like a medium riser than a 'street' manifold. Could this manifold completely wreck the performance or has anyone got any ideas why?

I'm going to venture a guess (and it's just a guess) that the new cam was not installed properly and needs to be 'degreed'. Or that it isn't really a 7122 cam...

I just played around a bit in Dyno2000. The manifold can make a difference, and it's limited in its manifold type selections, but the difference it shows between a single-plane (e.g. the original Torker II) and a dual-plane is on the order of 5-6% at 5000 RPM. Retarding the cam timing by 10 degrees can lose you 6-7% (again, according to Dyno2000 so don't take these numbers too seriously).

There's something very strange going on if your torque peak is at 4200 RPM - that's a stock cam kind of curve...

Have a look at compression. If it is low then find the leak. No leaks then figure out combustion chamber volume. Just a guess with new heads.

Thanks for the help guys. I think maybe it is a cam timing problem. It is very strange that the engine is much quieter now than before both on induction and exhaust noise. Maybe the valves are not fully open? Im going back to the dyno tuner!