how big of ones should i look for? and are the cnc's worth the money?

I've run both and have to disagree, never lost the guides due to poor workmanship on a set of Brodix.

Depends on the power you want to make,

If you call Bob he will most likely tell you AFR. I would recommend their 335's that are CNC'd, good flow and velocity. I have the 315's on my 524 with a slightly smaller cam. I haven't been able to really test the top end yet, but the acceleration is out of this world.

Agreed. Bob is designing my 578 right now. We are going with 335 cnc'd AFR's. Alum heads with good parts and a good port velocity. We are aiming for the 750 mark also spinning 5500-5700. Guy knows his stuff thats for sure!

You should probably talk to Bob Madera about the heads as if he has spec'd the cam he will know what head will be the best bang for the buck! Those camshaft numbers still kinda look like reversion to me on an N/A engine but if Bob says it will work , then It will work.

Next, want to build a good big power reliable big block 581inch -750HP marine engine, THEN DROP THE TERM CHEAP FROM YOUR VOCABULARY AND PRACTICES! A good marine 750HP reliable well constructed big block "AIN'T GONNA BE CHEAP" and you aint gonna find or build one on this planet! Try and you'll be back on this forum sometime in the near future whinning about the experience and problems. Not trying to be negative or critical here, just know that "Cheap' builds are just that! Don't build and buy your engine twice , its a costly and painful experience!

Best of luck on the project, hope you achieve great long lasting results!

Best Regards,
Ray @ Raylar

Im just like anyone else in this world i want the best deal possible. if i were cheap i woulda built my 454 to a 496 with a procharger that i still all own im my garage. im just looking for good true opinions from guys like arcticfriends and poker n run that have helped me out with there knowledge alot to this point.
As here in the prairie provinces in canada no one has any knowledge marine know how.
You will never see me in a competition as i live in nowhere land in canada. Im also not looking for a pusher on a product that they make the most commision on.
I was just in my small city at local race shops and there pushin me on edelbrocks. cause thats what they sell.
I just want some good ol truth from you crazy guys that GET summer year round. Remember i run a snowmobile from november till april too!
Its hard to keep all the #'s in my mind seperate as come november i forget all my boat knowledge and am running my sled.
Its hard to explain but i got 2ft of ice on the lake right now! I can always take a picture of the ice for you crazy BBC marine guys that never seen it, just ask.
And a BIG thanks to all the people that have helped me out with there knowledge I do respect everything you guys say!

Zeke,
There are a few simple tips to define the proper head for any application.
• Define realistic target performance parameters. Address the budget you are committed to and the collateral supporting components.

• Always select your induction path (carb/heads/ intake manifold/camshaft) to the scale of the engine. The scale is readily defined by a number of empirical data points. The displacement, volumetric efficiency, and RPM will define the necessary cross sectional area and delivery requirements.


Pitfalls to avoid.
• Flow numbers, used correctly, can be a useful tool in determining if the delivery will supply your targeted performance parameters, however they don’t supply the entire picture. They are a tool not an end. They can also be manipulated by test pressure and bore fixture size. Never use raw flow data as the sole criteria for determining head selection! It’s worth noting that exhaust numbers are often the most misrepresented/misused data point.
• Don’t get caught up in peak flow. Select a cylinder head that offers the best characteristics within the lift range you will be utilizing. There is no gain in selecting a cylinder head that flows 420+ CFM @ .800” for application exploiting a cam displacing .640” theoretical lift at the valve (closer to .600” actual after deflection and compliance). Keep you comparators within the useable range of valve motion. There is no upside to excessive CSA for the scale of the engine.You will find that will narrow your selection process.
Bob

I totally understand your special geographic situation and your limited boating season and obvious idea of the best bang for the buck thoughts.
I would say though with your very limited boating season window and remoteness for service work, tuning, tweaking and repairing, etc. I would recommend that you seriously consider purchasing a drop in "proven-ready to run" version of an engine and power you would like to have a possibly refrain from a do it yourself or local yokal type of engine build.
I am not looking for the job, but their are many good builders here on OSO who I am sure Bob at Marine Kinetics could recommend also who could give you that type of drop in-ready to run package and possibly save you some lost boating season trying to dial in a bigger horsepower marine engine.
Just my two cent opinion here.
Good Luck!

Best Regards,
Ray @ Raylar

That would of been the smart thing to do was buy a drop in. but then id miss all this fun! looks like there calling for a few inches of snow here on saturday so i have nothing but time.