Firewalker

I currently have an old tired 330 with Imco exhaust and crossover water system, I plan on upgrading the engine.

I am an outboard guy, so I need a lot of help.

My thoughts are this, Buy a new marine 502 long block, add a cam ( and associated parts ), intake and carb. Then dress it with my current cooling system, exhaust and ignition.

So if I buy a base 435hp 502 long block, what parts do I need ( numbers would be cool )..... I have been doing a little reading. so hear are my thoughs.

- Crane 731 cam
- Comp 929 springs
- ARP 7/16 rocker studs
- Highland shape roller rockers
- Edelbrock rec port air gap intake

Now I need to know what other parts I need and what carb. Will this combo work, and what kind of hp can I expect..... and if you would make some changes what would they be?..... I am looking for 500hp or more.

Thanks

RT

cstraub69@comcast

What about taking your block, sticking a 4.250" stroke crank in it, boring cylinders to 4.310" will get you 496 CID. Put a fresh set of oval port Merlins on it, air gap is a good choice in intake, a good marine 850 carb, a mild hyd. roller in the 600 lift range and high 220 duration range. Maybe more cost effective.

Chris

articfriends

iTrader: (1)

Unless you own the harland sharp rockers already i would go with crane golds,the last harland sharps i bought looked like blem's,word is they are now made offshore,good luck smitty

blue thunder

I like cstraubs idea but worry some about cylinder wear due to the rod length to stroke ratio. Any problems in that area experienced cstraub?

I would choose comp cams pro magnum rockers. Weather you buy a crate or build a custom really depends on how mechanically adventurous you are. I have read a lot of good things about the cam you selected.

BT

Mr Gadgets

Years ago I was headed in the same direction you are. I bought a GM 502 short block. Put a set of Merlin iron heads on it with Valako Wedges. First roller cam didnt work very well. Switched to Ultradyne roller cam and had good luck with them. If I were you, I would look into a short block, put some decent heads, Dart, Merlin, AFR and a hydraulic roller, good intake and 850-900cfm carb. Good headers and you will make 600hp without too much problem. I have used stainless steel roller rockers from Crower and except for alignment issues they have worked rather well. They fit under stock cast valve covers and I have yet to break one. I have broken about everything else but a rocker.. hmmm . I do think it is a good idea to open up any crate motor and check it out. While your at it, ad a little piston to wall clearance, if you plan on making any serious power. Mine were a little tight the first trip around.
Take your time and do your home work. Look at combinations that have worked for others and find out what reliability problems they have had!!

Good luck

Dick

formula31

Dont skimp on the valve train. Buy the best valves, inconel exhaust and severe duty intakes. Marine clearances, cylinder, piston pin, valve seat, all important.

cstraub69@comcast

BT,
With a rod/stroke ratio of 1.5 to 1 it better then a 400 and a little worse then stock. Experience with this combo of a Square engine is very good. I just cammed a twin engine blower combo for a customer where a pair of these had been N/A for 5 years. He said everything looked good and if not for the change in pistons for the pro chargers, could have gone back together. If my 310HP ever goes, this will be my choice, can't beat the torque.

Chris

blue thunder

That is what I was thinking. Serious leverage with that lower ratio. Good to hear the wear characteristics are acceptable. May go the stroker route over the winter.

BT

RonS

when you talk about marine clearances, I assume you mean in the block. Could anyone be more specific as far as numbers etc.

formula31

Depends on the type and manufacturer of the pistons. On the forged TRW's I use, I shoot for a minimum piston to wall clearance of .0055. .001 on the floating wrist pins and .021 ring gap on a 4.28 bore. On the heads, go for wide seat on the exhaust valves, around .090 or more. That helps cool the valve.