Engine is dying so mine as well pull the 454 and build it up. I'd love to get to 500hp. Already have 496 merc alum exhaust manifolds, 188 GM rect heads (which I believe are same as 502 500 hp heads correct?). Thinking of going to single plane intake, 60 over flat-tops, stroker crank, rods (all forged stuff of course)roller lifters, rockers, cam. Any cam suggestions?

I just got 520 out of mine with dual plane and oval port heads. Flat tappet cam.

You should be able to get way more than that with a roller.

The oval port heads are going to be better for you though. The single plane will be nice.

Did you mean to say the rect heads will be better? Im trying to work with what I already have, so i'm going to try to work with the rect heads. trying to mimic closely the 500hp 502 best I can.

The squatres are only better with more displacement or cams. In marine engines the big chevy or Merlin ovals are etter except for maybe that last few rpms up close to 6000. Ask around on the board. Those ovals are better overall in the middle and down low, and they don't cost enough horsepower up top to make a difference.

If you are going with the squares, you might want to stay with a dual plane to help in the mid range. 500hp is not a very hard number to reach with that engine, but remember you are going to get way better torque numbers with that 4.25 crank then you are with that 4" crank and that is what you want.

Its a heavy boat for single motor, so down low and mid range is very important. In fact I will rarely run over 45 mph, I just like to know I can hit 60-65 mph if I want to. Want to be able to cruise at 40mph with 1/2 tank gas, 4 people and gear aboard effortlessly. I currently have a GM dual plane for rect heads so I might stay with that and see how it runs. Holley 800 will be in order as well.

I just dynoed my 496 my a 750 and a 850. There was no change when we went to the 850. More carb than the engine needs only wastes money.

Cam suggestions:
1) Bob Manderra (RMBuilder)
2) Crane doesn't make it anymore but if you can find a Crane '731' cam, buy it.
3) Crower makes nearly the exact same cam as the 731. It's part number 01404LM, Valve lift is IN .585/ EX .612. Duration at .050 is IN 236/ EX 245. Lobe separation is 110 degrees instead of the 731 which is 112 degrees LSA.

You'll need a better intake, stock ones are garbage. get an Edelbrock Performer RPM Air Gap or a Victor Jnr if you have to have a single plane, most Dart, World, Brodix and Merlin intakes will be just too much for the RPM you're looking at. If you already have the rect port heads don't worry, they'll still work but you'll deffinately need the best intake to control the flow.

I'd recommend a Holley 750DP Marine carb but be prepared to swap jets until you can get from 2000-4000rpm without coughing of spluttering if you hit it.

What ignition are you planning on running? Avoid MSD 6M in my opinion.

Good luck, let us know if you get stuck!
John

I was just planning on reusing the stock Thunderbolt ign with MSD coil. Thanks for the cam suggestion.

I'M JUST SAYING IF YOU ARE GOING TO GO FASTER YOU NEED TO BUMP UP THE COMPRESSION TO 10:1 YOU WILL HAVE TO RUN 91 OCTANE ALL THE TIME BUT ITS WORTH IT CAM LIFT SHOULD BE IN THE 632 RANGE AND DURATION NO MORE THAN 252 OR 262 WITH A SINGLE PLANE DART WITH A 1050 DOMINATOR IF ITS IN THE BUDGET AND GET A BETTER IGNITION SUMMIT RACEING 1-800-230-3030 HAS A COMPLETE STRIP AND STREET UNIT WITH COIL BOX AND DISTRIBUTOR FOR $326.95 AND YOU SHOULD GET A LITTLE OVER 600HP. TEAGUE MARINE SELLS THE CAM ITS CALLED A STAGE 3HYDRULIC ROLLER 661-295-7000 TALK TO ERIC TELL HIM ERIC SENT CHA FROM 310 EXPRESS

That's fine. SRP or JE makes a 9.5:1 piston. That is plenty of comp to get you over 500HP with a decent roller cam. It will be higher if RMBUILDER designs it for you.

Merc tbIV ignition is Ok also, It is better since you can get parts at local stores later on if you need them on a weekend etc.

Have some port work done to the exhaust side of those heads if you have some extra cash.

You'll be fine with that. Later on in life if yo uwant to go bigger, you can use the cranks and rods in an aftermarket block and a new set of pistons and go 540-565CI.

Use those old heads and still make over 600HP.