how much HP gain will a lg4 get with heads.

 

This is the wrong board to ask that. You'd probably have more luck in one of the engine boards.

 

Thats a pretty broad question... can you be a little more specific?

 

Just heads? Not much.

Improvement in the heads is needed in order to take advantage of other improvements. The order of importance goes something like this: 1) Air cleaner; 2) exhaust; 3) cam; 4) heads; 5) intake manifold.

You can justify #1-3 without 4 or 5. However, 4 or 5 without #'s 1-3 is a waste of time/money.

You don't need to replace the heads, although that's what I did. Basic porting with 1.94" instead of 1.84" intake valves, better valve springs, and screw-in or pinned rocker studs will make a vast improvement.

 

The heads you have now are not your problem. The exhaust, intake, and cam are what make your engine a non performer. The LG4 actually has desireable heads for a 305 and can be prepped to make more power than your 305 will ever make. If you keep your 305, keep the heads. Replace the cam, intake and exhaust to make power. The heads on an LG4 are basically at the end of the "weak link" list of stock parts.

 

perfomance heads

 

Nothing

Unless you do a whole bunch of other things first

You might even slow your car down

Listen to what they're saying, it's true

 

The heads that are on the 305 will be performance heads enough for a 305. Have them machines for 1.94 intake valves, better springs for a good cam, and screw in studs. That or go cheap and pin your studs.

 

Just go to a yard and get some 305 castings for your year, have them done up, port and polish them, make them nice. Do what LJ said to do about the valves and what not. Put them on when you are ready. That's essentially what I did.