Just finished mine.

Flowed 358 @ .700 int, 231 @ .700 exh.
I blended the bowls, radiused the SS radius and worked the guide bosses on exhaust. Not a lot of work. Left the runners alone.

Put in 11/32 valves (.100 longer)

5 angle intake seats, full radius exh seats.

Milled .010

One thing to remember, HP500 heads are 088's, but are not 118cc. Merc worked the chambers out to 122cc's to keep compression down below 9 to 1. I should get around 575 HP, and over 600lb torque.

Bullet proof motors if done right.

Thanks for all the data guys, I'm torn between using my present heads, and buying som Alum heads, (concerned about saltwater corrison issues...)
Dean

If you go with Aluminum, have the water passages hard anodized and you'll be fine. I think its about $100 to have that done.

I have a HP500EFI Vortec M3 supercharger,EFI,intercooler,pulleys,remapped ECM for sale
[email protected]

That is a good idea.
Thanks,
Dean

I went the 509 ci route which increased compression. Cam, Pro-form 950cfm carb w/ super suckers. Kept stock heads and ended up 589hp. Love the new carbs. Starts and idles like a fuel injected engine

Really nice #'s for stock heads!

That's pretty impressive.. Now you have to give us some details. Head work, Cam, etc. Build sheet and Dyno sheet would be even better

More More!

Tthe Edelbrock (marine) heads are anodized

Marine Duty Performer RPM 454-R

Heavy-duty, 1.89" Inconel exhaust valves provide added durability for marine applications
Hard anodized black to protect the aluminum in the harsh marine environment
Sold with valves only to allow for valve spring choices
Match with an Edelbrock Performer RPM manifold, Performer Series 750 cfm marine carb and Performer RPM cam for proven performance
Smaller-than-stock 11/32" valve stems promote excellent flow and lighter valve weight