SR-24

jdnca1, Thanks, I might try contacting you for help with cam selection when the time comes because that's one area I don't quite understand everything that needs to be happening and why.

jdnca1

SR-24;

Anytime, I'm not an expert by any means but have direct numbers to several that will give you some great insight on the correct cam. The first thing they will want to know is CR, heads, flow, intake, carb, expected rpm's, etc. But you really need more head, thats where most of your power is made.

26scarab

SR-24,
Go with the Brodix intake over the Dart

Jdnca1,
Why go with the bigger heads ? I thought that was the problem with making power on a marine engine (low rpm) there isn't a good enough head unless you want to spin it past 6000.
That's why you go with a smaller runner and port it to make it more effienct at lower rpms. I've got Oval port Merlins and they have been welded up and ported and I still have to spin it relatively high 5800 to make any power.
I'm not an expert but have friends that are and I have learned a little thru osmosis

jdnca1

26 scarab;

A 540 inch motor needs flow to make power. If he only wants to turn 5000 r's then I agree with you on using small heads. However, when you are talking higher compressions, large roller cams and Dominator carbs you need a head that can support a 540 inch motor (a 454 is a different story) or the rest is a waste, because airflow will be severely restricted especially @6,000 rpm.
It really depends on what a person wants. But if someone is going to spend the money, it really doesn't cost anymore to set up the motor to make some power and you need to turn it to do so.
I know someone running a 540, 10.25:1, with Dart 345 Pro 1's solid roller (270ish duration) and 1150 dominator that makes 775hp on pump gas. Should be pretty easy to duplicate.

timucin

in my opinion keep the comp low.that matters maximum 20-30 hp but it is safe.you alredy have lots of hp ,do not risk your engine and loose the idle just for 20-30hp.I made the same mistake 4-5 years ago . was using a 502 with 11:1 cr very rough idle, believe me it is headache!!! when you enter marinas or try to pick some one ,engines always turn off-you always have knock problems-you should make 1500-1700rpm idle which is serious trouble for drives....etc.....etc...
just fly low and enjoy your boat...

WETTE VETTE

Here is the question. At what point (rpm, cubic inch, compression and cam) do oval port heads just run out of breath? I built a 454 with 9:1 compression, hydraulic cam, worked over 049 big valve oval port heads, matching intake, 228/235 dur at .050 with .540" lift hyd flat cam and headers. The boat was a blast and gained 10 MPH over the stock 330 motor and put me in the mid 70's with a 210 Baja Sport. This combo worked great down low and pulled good to 5400 rpm or so. Now compare it to my current 496" motor that is about 22 MPH faster than that 454. It has fully ported 325 pro 1's, solid roller 272/280 at .050 and .714" lift, 13.16:1 compression, 1175 CFM Nickerson Dominator, among a bunch other HP goodies. How would oval port heads do on this motor? I think they would give mondo low end and would start to suffer at around 3500 RPM compared to the rect ports. I think a milder 540 could run very well with ovals as 26Scarab and KAAMA have shown, but you are at the outer limit of those heads. It is my opinion that a 325 CC runner is ideal for a mild 540 at 5500 to 6000 RPM on a boat motor. A 345 will be ideal on a 572 to about 600". Above 600" you are probably looking at 360 to 400 CC to keep them breathing. Just my opinion and you know what they say about those. Just like a-holes, we've all got them. I would like to hear jimv's opinion as well as some of the other OSO gear heads. I hope we are helping this guy!

SR-24

I agree with you guys on the smaller heads. I don't plan on turning the motor past 6,000 because the cam is only good to 6,000 and I bet it will be more like 5,800 and that's why I said I planned on using the 310cc runners. I will continue to ask around and yes I wish Valako or somebody with alot of experience would read this and tell us all. I am currently running the Merlin 269cc runners on my 502 with a Merlin dual plane and a short duration cam because of silent choice (don't worry, I'm losing the silent choice) and it is very strong. I imagine the torque is astronomical compared to the horsepower though. I read in the Big Block Marine book by Dennis Moore that you needed to be able to turn the stock 320cc runner chevy heads 6,000 to 6,500 before you would benefit but who knows. Thanks to everybody for the input and keep it coming.

jdnca1

SR-24;

I would talk to DART. I'll bet they tell you the 325. I also have the Dennis Moore book and there is a ton of useful info in there. However, it seems he focuses more on the "smaller" cube Big Blocks. Food for thought...Let us know what you find out.

SR-24

I will. I've got some emails out to some engine builders now, just waiting for replies.

FloridianSon

Sr-24 if you don't mind me asking what are your cam specs.The specs on chevy high performance 502/500 that used oval port heads and is what I went but I have merlin 269. chevy part number 12366542. 224 intake 234 exhaust .527in .544 ex lift and 110 LSA install on a 110 center line.