My engine pulls pretty good up to 4700 -5000 rpm depending on load. I'm thinking my heads might be holding me back. What do you guys think and what heads would you suggest. Here's what i got, sbc bored and stroked to 385,6 in rods,rpm air gap intake,crower roller cam adv.lift 525in 542ex , dur at 50 221in 228ex, lobe sep 115, roller rockers 1.5 ratio, 750 cfm carb and summit cast iron vortec heads,67cc combustion chamber volume,170 intake runners,1.94 in,1.50 ex, glm alum ex.silent choice. What are your thoughts on this. Any suggestions are appreciated. Oh ya my cr is 9.4 to 1 and my all in timing is 34deg.

What size boat, how much does it weigh, what drive, what ratio, what pitch prop, have you tried a smaller prop, was the motor dynoed, what rpm is the peak HP, might help.

Maybe this will help.

http://www.dartheads.com/tech-articles/port-volumes/

I don't have experience with those heads, but that cam will be pretty much done at that rpm too.

With 9.4:1, you could go up another 10 degrees at .050" and narrow up your LSA up some.

Your exhaust probably won't deal with that, so......................

Yes you are right by design vortecs quit around 5000.boat's car's whatever..... here have a read from one the designer's

http://www.nastyz28.com/forum/showthread.php?t=56505

Cam and heads, like everyone is saying, single plane will help, too. Is gross lift for 1.5 rockers? I've always ran 1.6 or 1.72 in SBCs.

Whats the p/n for the heads? Any port work done to them? Any casting numbers on them?

http://www.nastyz28.com/forum/showthread.php?t=56505[/QUOTE]

I've been on NastyZ for years now. Great guys!

Heres a Hotrod magazine build using an aftermarket Vortec head. Impressive numbers to say the least!

http://www.hotrod.com/events/coverag...c-small-block/

Heres a Hotrod magazine build using an aftermarket Vortec head. Impressive numbers to say the least!

http://www.hotrod.com/events/coverag...c-small-block/[/QUOTE]

Heads in this article flow about the same as stock vortec heads

The boat is 23ft long and weighs around 4500lbs dry. Alpha 1 drive 1.5 ratio running a 19pitch mirage plus. I've tried a 17 pitch mirage the rpms went up to 5500 with no gain in speed.The eng has never been dynoed. read the dart article and thought the afr 190 vortecs would be a good choice if indeed my existing heads are holding me back on the top end