The six pack engine in my GTX is 708 horse on pump gas. I used a 73 block, installed cross bolted main caps, put bushings in the lifter bores, bored .030 over, 4.5 lightened stroker crank and assembly from 440 source. Solid com roller cam, 633 lift I think, 1.6 crane rockers, ported Edelbrock RPM heads. Head flow 327 on the intake side. Port matched the intake, installed 1/2 spacers on top. Do not mess around with the top side of the manifold. Leave it as cast. Now I sent my carbs out to Gary Williams and had him work them over. I wasn't happy with the throttle response so I got a set of mechanical carbs. Sent then out, very happy. Now the stock air cleaner with a paper filter will cost you 40 horse. A K&N filter robs 22 horse. My 535 is all done by 6000 rpm. When we dynod my engine, we tried 7 different manifolds. A single 4 barrel ported made 15 horse more. A tunnel ram made the same, just pulled more rpm's. Tried a crossram, that castrated the engine.
When you say you went to mechanical carbs are you talking about the ones that have accelerator pumps on the secondaries or just straight mechanical linkage?
Thats quite a power loss from the air filters- more then I would have initially guessed. Maybe I shouldn't be surprised the element doesn't look very tall so maybe not a lot of area to it overall...
