Are 350 heads any better than 305 heads both off tbi engines 305 stock headers 4 barrel intake with adapter plate to tbi

 

Not 100% sure but I don't think you can use 350 heads on a 305 unless they are 58cc combustion chambers. This is due in part to the bigger combustion chamber over shrouding the valves. The 350 heads have 76cc chambers I think. As far as flow is concerned I don't see one outdoing the other as they are both swirl port heads.

 

Thanks I have 350 out of 91 I'm gonna build for the bird but the heads ain't the best I just wondered if the 305 get any free power from them

 

You run into valve shrouding issues. Pretty sure the 350 valves will hit the pistons on a 305.

Your best bet would be to pick up a Vortec Intake and 58cc Vortec heads. They'll outflow just about anything except the high-end aftermarket stuff.

 

The 1.94 intake valves won't hit the factory pistons or cylinder bore even at .500" with a modest duration. Never tested a massive 240+ @ .050 duration cam, but have tested into the mid 230s using 6cc relief flat top pistons. The intake valve will clear on up to about .650-.700" or so.

 

So would it be worth even doing?

 

No. Simply because 350 heads are either 64cc or 72 occ and your 305 had 58cc chambers. You will lose compression and horse power. It's basically a terrible idea unless you plan on running boost through it.

 

Okay thanks thats all I need to know

 

If you have money to spend, port your 305 heads and install 1.94 intake valves. This is what super chevy did to get get 300hp out of their 305 and will get the most out of your current heads and is going to be your best bet short of serious aftermarket stuff. They just don't make high performance heads for the 305.

 

Trick Flow 175 is a high performance cylinder head for the 305, but since he is planing to build a 350 ...