BajaRunner

Ive got my boat in getting the valve springs and headgaskets done. Is it worth it to get the heads bowl ported?? Its an extra $200 an engine. Id like to get some performance, just wondering if it was anything noticeable.

baja36ft

I Would Do The Exhaust Ports And Mill The Heads
And Bring The Comp. Up To 9.1 0r 9.5 That Will Wake
Up That Motor.

KAAMA

iTrader: (1)

Yes, bowl/pocket porting--- remove/round out the rough edges, clean them up a bit and pay special attention to the short side radius's. You can do a little more to the exhaust ports as "baja36ft" has suggested because they are pretty crude as they come cast from GM. Take them to someone who has some familiararity with head porting. Might be worth 20hp or so. If they were mine, then I would have them done,---but that's just me. Every little bit helps. Have fun!

BajaRunner

would a standard "milling" do that, or do i need to have the done a little more.

If I get that done, do i have to switch to super?

And what kind of gains would i see?

ROTAX454

What GM heads do you have? Also, before you mill the heads, you should have the chambers measured for volume. My new heads right out of the box where not to spec (there is a tolerance level). Two heads where 116cc and second pair where 114cc. GM spec was 110cc. I had them all milled to achieve a 112cc volume across the board.

Bubbletop409

BAJA Another thing you may want to check while you have the heads off is the "quench area". That is the space between the flat portion of the piston and the head surface, with the piston at TDC. Measure from the deck surface to the piston surface and add in the thickness of the head gasket, that will be your quench area. Ideal quench area is in the .038 to .040 range. This can altered somewhat without machine work by using head gaskets of different thicknesses. Cometic offers their BBC marine gaskets in a variety from about .027 to .060. Optomizing the quench will give you better combustion, and may increase your compression slightly also, depending on how far down the piston is in the bore.

baja36ft

NO, STANDARD MILLING WILL NOT DO IT AND YES YOU WILL
NEED BETTER GAS I KNOW HP500 SHOULD BE 8.75 COMP.
BUT WHEN MINE WAS CHECKED IT WAS 8.4 WITH 75 HRS.

BajaRunner

I talked with BobL whos doing the work. He said the same thing, they are usually a little low. Hes going to shave them .020 and bowl port the heads. Hopefully it will add a little. Mine have 370 hrs on them, so hes doing a valve job as well. Maybe with all that, Ill see a little gain.

baja36ft

I Would Also Use The Cometic .027 Gaskets.

BenPerfected

My opinion is you are probably wasting time and money. JimV frenquents this board and he is a VERY knowledgeable head porter and he builds marine engines. You should consider whatever he recommends.