Last year i purchased a set of used HO heads,How much will i gain on my 305.My car is a 87 LS 305 4bbl.last year i installed true dual exhaust,w/full legnth headers, no cats to breath better..The heads should be, in my opinion gone over..They were supposedly done, but i want to be safe.And have them done..How much will i gain??

 

Without porting and polishing them, unless yours are in really sad shape, Nothing. Really no difference between the l-69 heads and the lg4 heads.

 

the 416 HO heads are the best heads to start with for sure but can use some work.
but it depends on how much money you want to spend. 1.94 intake valves are a good upgrade. and a good port and polish job.depending on what cam you want to use you may want to get screw in studs.