Long time lurker, first time posting, glad to be here. I have procured parts for a 509 project engine for my first powerboat. I have a Dart Big M block with forged rotating assembly. The pistons are flat top with 4.5cc valve relief. I would like 9.5-10 CR which means i will need 110cc heads or smaller i think. I have a hydraulic roller camshaft with the following specs: 234/242 .610/.632 112 If I can use it fine, if not, oh well. I want to get the most bang for my buck. With the research i have done i see that 310cc canfield heads are a good buy along with an airgap intake and 850 demon. My budget is pretty tight. i buy parts on ebay from money made on side jobs. $2000 for heads, $200 intake, $550 for carb. What can ya'll recommend for the top end of this motor. I'd like to see 600+HP with a nice broad torque. I hope to put this motor into a 26' CAT someday. Thanks for your input and once again, hi ya'll.

Use a Dart single plane intake. I've seen a lot of used ones on this site. Other than that, your choices are fine. Don't forget a good oil pan and cooler.

I've got a 10qt oil pan. Will i still need a cooler with that much oil? Will the single plane be too much with such a higher rpm operating range compared to a hi-rise dual plane. I've seen so much controversy over the two. My machinist says dual plane but he does not do strictly marine, mostly blown alcohol and other drag car types of motors. I like the input OSO has due to the marine experience. Thanks, Dave

I hear the Brodix Single planes out perform the Darts.
I am changing mine this winter from Dual planes to Brodix Single plane.

Mark

pistons .023" down from deck surface @ TDC: 8.97:1 with 110cc heads

pistons @ zero deck: 9.35:1 with 110cc heads

Based on 4.500 bore, 4.000 stroke, .038" gasket thickness.
Head volume figured with sparkplug in place.

mc

I know of a guy who built a 509cid engine with the same hydraulic roller cam specs as you, 950cfm Holley, 9.1 comp ratio, Air-Gap intake, Dart 308cc heads with only some clean-up around the bowl/valve areas and it made 563hp @5700rpm on Tyler Crocket's dyno a few years back. Not sure you will quite hit 600hp with a dual plane intake such as the Air-Gap on a 509 for what you're tyring to do. The Dart single plane intake might be a good option. Maybe others can help shed some light on the subject. Welcome, and have fun with your project.

Yes, you are still going to need the oil cooler.

The single plane is going to start making more HP/Tq at about 4000 rpm on up over the dual plane. Using 5500 as a WOT, the single plane is going to be showing ~25-30 HP more than the dual plane. In the 3000-4000 range, its going to be about even. remember, in a boat you really don't need to worry about the power below 3000 RPM, as that is the speed that most boats get on plane, compared to a car that will be spending a lot of time at that RPM. You will usually be cruising between 3-4500 in a boat, and when you want to go for it up to say 5500, the single plane will blow the dual away.

We put together a 509 for my sisters Chevelle , 502 crate motor bored out, 10.5:1 cr, Iron heads done to death, air gap intake single plane, 710/690 solid roller cam with 110 center line ( same as our 540 boat motors) 1050 street demon carb and all the other good stuff as far as hardware goes. 675 hp ,600 ft/torque. This car is a driver, full interior, all steel , 390:1 rear end and runs 10.90's when tuned for it. I would build this same combo for a Boat .

Would large oval port heads do me better than rectangular ports. For example, the large port AFR heads compared to their rect port heads. Also, should i ditch my flat top pistons for some small dome profile pistons? There seems to be more 118cc heads out their than 108 or 110 cc heads which i know you can custom order but i usually buy gently used stuff on ebay or where i can find it. Thanks, Dave

Anyone else with proven 509 combos? Thanks