mine are large oval port.. If you ground out too much meat in the exhaust port eventually it starts to leak. The original heads that came with the boat both went bad, both were leaking from the exhaust ports after pressure testing. So this time we went not so large on the valve sizes and no deep porting...The problem with new heads is that most if not all of them like world products, dart have raised the exhaust ports 1"....SO after you install your exhaust manifolds and risers nothing lines up again. 1" at the bottom changes a lot on top of the engine. Years ago I had Gil exhaust on a single big block with new heads. Gil made wedge plates for this type of situation. Try and get a wedge plate for stainless marine exhaust...or many others. lots of luck.

I think Brodix makes an aftermarket head that flows pretty decent, and still has the exhaust ports in the stock location. The heads are aluminum, however, so might be an issue on a raw water cooled application.

Yes, the RR (Race Rite) series for BBC's.

You'll never get to 9.75:1 with a 454 and a flat top. I don't know how you are getting 8.5:1 with a flat top and peanut port heads. Even with a 100CC chamber and a zero decked block, you'll be lucky to see 9.25:1. A stock 330HP merc was 8.0:1

I ended up with 781's .030 shaved from heads giving me chamber of 108cc and .023 in the hole on flat top pistons. 30 over bore. Don't have a calculation on compression but guessing 8.5 - 8.75 on compression.

That would make a little more sense if your heads cc at 108, and the block is .030 over.

With that combo, you're about 8.4/8.5 ish with a typical .040 head gasket. You could get that up a bit with a thinner cometic head gasket, or if the block is going to be machined, have the decks milled a bit. Nothing wrong with a 8.75:1 engine. Mercury did it on many engines. I'd enjoy the 87 octane fuel and run it.

8.4/5ish did you run that through your computer or is that an educated guess?
Any idea what I would pick up with a thinner head gasket?
Thanks

Merlin made the majic aftermarket boat heads . Under a grand . Cc your oval ports , use the drugstore kiddo syringes if you cant get a moroso acrylic or comp big glass, 9cc can be the difference between yea and nay
Big john got over 500 out of peanut ports at under 5000 rpm , yea he could make hummers do wheelies in street trim , but the peanuts its mostly in intake port volume and cam cause your exhaust is still going to suck anyway
Your never going to be king with a bbc and flat tops but with some science you can get within spitting distance of the mag on wet exhaust boat app without pulling the motor

Did you cc those? I've cc'ed probably 7-8 781 heads (exhaust issue mentioned above got me), and I've never seen one below122 cc chamber - and that one had been shaved previously. Starting with that, you can't get to 108, not enough deck thickness. Online, they list 781s at lower cc's, but those are inaccurate when considering everybody's actual cc readings.

I personally did not cc them, the machinist told me that is what they cc'ed at. He said he measured therm.