Just wondering what would the best heads for my 509.Short block is simular to a gm crate 502 short block.Aluiminum or steel?Runner size? Valve size?I would like to keep rpm range at around 5500 max.Any help would be great.
Thanks Dave

I went with Iron merlin heads with 345 intake runners on my 540. Cp Performance has the specs on their web site. I bought them through a local automotive speed shop which gets me pretty good prices.

Check, for naturally aspirated 502 inches I would go with something like a 308 or 310cc intake runner size. I use a 310cc head and I'm running a pair of 540 cubes. 345cc is okay but you'll be sacrificing torque which is the HOT ticket for a boat engine. It's your preference on iron or aluminum, and I would go with something like a 2.25"/1.88" valve size. Some one else may chime in with more wisdom about your engine components. But remember, TORQUE is what moves the MASS...not horsepower!

I agree with Kaama. The reason I went with my heads are my boat is light and I was planning on going back to a blower.

Kamma engine will be natruallly aspirated
KC,did you buy your heads assembled or bare.Do you guys think ss valves would be ok on the intake and exhaust or should I go with iconal(spell) exhaust?
Dave

If you have a light boat you will benefit from running the larger runner. I run a ported 325 pro 1 aluminum head from Dart on my 496". This may be a good compromise especially if you are thinking of going with a bigger motor in the future. Let us know what you choose.

Checkmate, call JimV and he can help answer your questions even if you don't buy anything from him. He did my heads but he didn't use inconel valves and he gave me his reasons behind it plus I run Stellings DRY headers...they're fully jacketed but the water does NOT mix with the exhaust gases. JimV's number is: 616-735-0800

I agree with Kaama.

Inconel valves are not a necessity with dry headers, otherwise cars would use inconel also.
Inconel is less prone to crack or shatter if reversion occurs than stainless or heat treated steel.

The Merlin 310's for a 509 naturally asp. is the way to go for "out of the box performance". The 345's will work just fine, but as was mentioned you'll loose a little at the bottom and gain nothing at the top. For a 509 at 5500 r's the 345's aren't even tryin' yet.

The 310's come with 2.25/1.88's and that's fine to also. If you want to get into expensive machine work, you could get 2.30/1.90 and a bunch of other work done, but like I said, for "out of the box" cant beat Merlin.

As far as aluminum vs. iron...well, that's a judgement call on your part. That depends on type of water you run in and many, many other factors. My personal choice for a Sunday performance with little to no maintanance worries; Iron.

DAVE

Check- I agree with KAAMA and DaveF, and depending on your cam selection and exhaust, and how you want to use your boat, I wouldnt be afraid to go even smaller......If you are just wanting a sweet running motor with 500hp some of the oval port heads with a little work would be hard to beat If you want more, and still want to maintain decent performance throughout the entire rpm range , then go with the 310cc heads. If you have the cash, a competent head guy, can retain most of the advantage of a smaller intake port and make it flow like a bigger port[to a point], having the best of both worlds.
My ultimate daydream motor[naturally aspirted, that is], would have DART 265cc Race Series oval ports, full CNC ports, then sent to JimV for further tweaking....ending up at just under 300cc.....making 600hp @ a mere 5300 RPM.....TONS OF Bravo shattering TORQUE....giving everyone in the boat whiplash right after throttle tip in...............alright, I got a little carried away...a rea
lly cool thread could be called "DAYDREAM MOTORS"
P.S.-How do you insert smilies?

I'm gonna differ with you guys on exhaust valve material. Go with the inconel. I'm not arguing the brittleness versus getting a bit of moisture on a hot valve. It's all about stability at high temperatures. A car does not constantly load the engine like a marine engine does. In a car the exhaust valves have time to cool while the engine is coasting, or at elast not under heavy load. A constant load engine in a boat (or an airplane for that matter) retains a lot more heat in the exhaust valve, and that's why you really ought to use the better material.