Might be more power in an exhaust change. From what ive seen from some dyno testing on a 600hpish marine build, a good set of headers picks up 30-40 hp and about that in midrange torque , over a stainless marine/GIL type of manifold

I had a similar issue didnt listen to my motor man bought pre Assembled heads 20 hrs in hung three valves valve stem clearance was too tight had to fresh the motor world products Only would help with parts and the work order clearly stated for marine use so I total agree bare heads and build them up

I sucked a bunch of water back up into the motor complete refresh fun fun

We used tcast Iron heads and had Jim Valako touch them up. My suggestion is to call Jim and get his advice on which cast iron heads would be best for your combination. He got them to flow similar the the AFR heads.

32 degrees timing in your application is not enough lead imho.. Will put unwanted heat at the exhaust valve... You would be able to get away with this if the engines were 572's 598's or bigger cid... But in your application a few more degrees of lead wouldn't hurt you a bit!! Just my 2 cents

agreed!!! X2

Look at the short headers cp has will bolt up to risers
the manifolds are harder Gil style and i thought they where rated to 500 hp but I could be wrong

NA engines benefit from header tube length, diameter, collector length, etc. Same concept that goes back to the 450hp big blocks of the 1960s

imo,the engine quest 320 head would be a good choice,good head at a very fair price,if you want aluminum on a budget look into ak racing pro maxx 317 heads.afr 305 is also a good choice.as mild thunder already stated,the best cylinder heads won,t show much improvement if the exhaust system won,t let the exhaust get out.

How do you guys like the cmi e tops or lighting headers

Diamond Marine Thunder and Lightning cast headers (used to be KE) - make sure tail (including tailpipes) is 18"-19" long total length.

Thunder-N-Lightning Cast Aluminum Exhaust Headers :: Thunder & Lightning Headers :: Exhaust Systems :: Diamond Performance Parts