Give this 502/509 Combo Some Thought
 

I have basically a marinized 502/502 and I suspect the heads are my biggest bottleneck. With that being said, the current combo runs fine, might make a little too much heat with small combustion chambers, but otherwise a lot of bang for the buck. I'd guess 525HP as is and only has 15-20 hours on it.

I am looking for 300-500 More RPM before I start working on the drive, prop and bottom.

Current Spec:
502ci
9.6:1
Isky 238/248 .578/.608 on 114

290cc Runner 110cc Comb Chamber 2.25/1.88 Stock Alum GM Heads w/Stainless and Inconel and Comp 1.7 RA's

GM Dual Plane Intake
QFT Marine 850
Thunderbolt w/ HP Module
Dry Stainless Marine

It seems I can spend some good money on heads, cam and intake for maybe another 75HP or I can work on these heads a little, bump the cam up to the famous 741 and try a single plane. While I want to run a little faster, I don't want to sacrifice 3500 rpm cruise to get it. Based on my research, a well put together 502/509 is going to make 625 with some significant cylinder heads. I hate to cut a good set of cylinder heads down to make the compression necessary with my flat tops. I do have a spare block and crank to build a 509 out of but again, that's a lot of coin for 50-75 more HP than the current combo might make with work.

Am I right to think $1500 might get me what I want vs. $5-8k to start over and make a little more?

This is my light weight 27 that's running a best of 80 as it is. 90 would be fun but 60-65 MPH at 4K would be just as cool.

BM/MK had a dream about my current cam once. My lifters made a noise when when they were installed. With a dual plane, it has the torque of an RV cam but the sound of a super custom, computer software proven, 20 hr valve train cam.

What, not interesting enough for this crowd without drama?:food-smiley-007:

FWIW, Endeavor1 drove it this week and said I should leave it alone!

I have a very similar setup with 9.6:1, ZZ502 cam, and Eddy Performer heads and manifold. I don't know how the Eddys compare to yours, but when I spoke with MK he said that 600 should be easy and maybe 650.

Edit: 600+ with a NEW cam. The ZZ502 is pushing 500 undressed at best.

Do you know the basic specs on those heads?

I know that boat of yours is turn key and super fun to drive:wizard::noevil:

Those afr 300 cc oval ports would be awesome on that with 454-0 intake.

600-650 with zz502 cam? I'd love to see the dyno proof of that. Lol

For the sake of argument I'm hunting 600+. 502s. EQ heads. Off the shelf cams. (I know crazy right?) Merlin intakes and quick fuel carbs. Looking around 9:1.

600 HP isn't hard to make from scratch. I am just trying to figure out if I can get close without starting over.

I am tempted to just try a little more came and a single plane intake but again, I don't want to worry about heat when leaning on it.

I'm gonna have larger cams than you and I'm single plane.