Fresh 489, Cam from Bob at Marine Kinetics, 595 lift, 188 heads, 9.5:1 pistons, all forged bottom end,454 mag gm intake...23p mirage prop on a 5000lb Chap 2550 sx. Got a Holley 750 dp. Should I have gone 800 or 850? Great out of the hole, no trim tabs necessary, top end not there. Will try a 20p turbo prop tonight to see if that gives me some lift to get the rpms up.

If you can run a vacuum gage on the engine, at WOT you should be under 1" vacuum. If more your carb is too small.

Ask Bob, he will know best. I have a 489 with a similar cam and I gained 5MPH. I have a Holley MPI kit, 1000cfm TB and 42lb injectors. Make sure your air cleaner is big enough.

I have built several 496's with Bobs help. It depends on how many RPMS you plan on spinning that. I used 750 Bary Grants and propped it at 5,300 RPMs.

You never said what exhaust you have?

I agree with the others, call Bob!

Bob is currently building my cam and has helped me design 80% of my engine. You bought your cam from the right guy give him a call and he'll help you out! I was planning on running a 750 carb on my 440 bbc and Bob said, "no, thats a small block carb" From what I was told in that conversation, my guess is you need to step up your carb at least. I am going with a pro-systems carb, which I'm guessing will be around 850 cfms.

exhaust is merc 496 alum manifolds/risers with GIL silent choice diverters

spoke with Bob, sd I am way under carbed, he recommended at least 850.