I'm not a head porter BUT I also had a set of merlin vr rectangle ports (previously to my afr's) and they used the same exact exaust port as the oval ports,my motor had a hard time breaking the 700hp mark no matter how much boost I put to it and it was a 540. The exhaust ports are raised but flow virtually the same as most STOCK gm heads until they have a grinder put to them by a professional head porter,203 cfm at .600 lift is what the stan weiss chevy head flow dat base shows,most good flowing bbc head exhaust ports are more like 260-320cfm,a 25-30% difference. They are restrictive,if it was just the exhaust ports I would say have them ported but you also have mismatched intake ports that would be ok on a N/A 454 but again don't flow enough for a blown application,Smitty

Oh yeah.....I forgot to mention the 468 made that power with full port GM rect. port heads we ported in house. The camshaft works fine. 232/240 is what I run in my lawn mower.

The exhausts on my AFR's after being worked by Jim V flow 290 at .6 lift. Your Merlins are probably flowing around 200 at the same lift. That's about 45% more. With the mismatch the intakes are somewhere around 250. Out of the box, most small rect. alum heads are 350 or more at .6 lift. There is a lot of hp to be gained with a head swap.

If you want to stay with cast iron, talk to JimV about porting a set of the Dart IE 308's. These heads supported 820+ HP in 505 ci NA with a 323 cc intake runner; the acceleration is absolutely awesome. JimV had the flow on both the intake and exhaust at industry leading levels that were as good as any similar sized CNC aluminum heads.
Cast iron has numerous benefits vs. aluminum in a marine application.

THANKS EVERYBODY HERE!!!!
Any input on the AFR steel heads?
Should I look at a 360 or a 320 runner on this application? Power is the # 1 goal, and being me, I would choose the 360's however I need to live with it cruising 85% of the time....And, I also want to be able to expand from here and not end up with a dead end head like this again....

Small runners for a small engine. If you were drag racing, 360's would be good for 8000 rpm's on a 489.
Arcticfriends is getting 950 hp out of a supercharged 540 with AFR 315 heads.

Ben Perfected, How fast you going now? Can you post some pictures of the boat / engines? thanks

Jim,
I will post some pics in early June on my next trip to OH. Last weekend I got the boat out for the first 2007 ride. We briefly ran to 100 MPH and backed off as everything is is at zero hrs...couldn't wait! Between your newest heads and the Wilson Manifolds prepared Merlin X marine intakes, this is the most responsive package I have have ever had...only took 20 years! It did take $1100 of work to fix each intake. My initial impression of the Peterson wet-sump oil pumps is also positive...still dialing in the initial pressure settings.
MRE's Spinton tested valve train includes a 55 mm cam, Crowler .937 lifters and 7/16" tapered .180 wall push rods. This stabilized combination should set a new base line for high performance BBC marine valve train longevity, except maybe for Mercury Racing.
The 820+ HP is not "in the boat" real as we used 2.25" ID dyno headers. Real world in the boat with my current CMI Sport Tubes is about 780-785 HP.
I am thrilled with the performance of your heads and your ongoing contribution to my project. If the A & B classes still existed, we would be hard to beat in 2007!
Your intake runner size is proof that size does matter...
Thanks,
Sprague

A 360 is too big. Like I have mentioned prior.....that everyone seems to forget here is, you have a BLOWER on top this engine. Give me a call if you need some advice before you get confused. I will be more than happy to help you in any way I can. We do our own cylinder head developement in house for over 50 years. You made a great point...." I want to be able to expand from here". PM me for more info.

Thanks,

Dean Gellner
Gellner Engineering Marine Power

Sprague, That's awesome!