danielthelen

What Kinda power difference would small vs larg oval port heads have with the same set up? It has a comp 262 extrem cam.

thanks

BadDog

About the same as large vs small.

I do not have your answer but those who do will need all the specifics of your setup including boat weight and intended RPM. You may also want to do a search in this section.

danielthelen

I have two different casting number heads. 336781 and 353049. If it's worth putting the on, I will have to find a pair. These heads supposly come off a Mairne engine.

Sadist

I've always thought the 781 and the 049 heads were real close...
Check http://www.mortec.com for some more info on GM casting no's
353049.....73-84...oval...OPEN...454, 122cc chamber, 255/119cc ports
336781.....73-85...oval...OPEN...454, 118cc chamber, 256/114cc ports
both of the casting numbers are what I consider the "large oval" design, versus the "peanut port" style that was popular in the 80's to the gen series engines.

formula31

And upgrading those head to 1.88 and 2.19 valves will help a lot too. I think the stock valves are 1.72 and 2.09 maybe. Ive actually taken mine to 2.25 which is about the limit. Some bowl work, unshrouding and cleanup in the runners and they do well. Of course, by the time you get done with all this and hardened seats and bronze guides and spring pockets you end up close to the price of aftermarket. I havent seen any performance difference between the 049 and the 781's.

danielthelen

Could I get away with running the missmatch heads? I only have $80 into the head right now. They were just gone threw and look good.

dan

formula31

Hmmm, of course the safe answer is no but, they are so close I would try it on a tight budget. Measure the combustion chamber sizes and if they are close you might get away with it. Dont mill just one head or you will have all kinds of other issues such as pushrod length and intake manifold fit. You will have to check spring installed height very carefully and adjust if needed. Check plug color closely from bank to bank after break-in using proper methods. Im sure Ill get killed for even suggesting this mismatch.

danielthelen

Here's what i'm thinging. Mybe I can polish the combution chamber out on the 781 to 122 cc. I'm thinking I want 9.0 to 1.0 compression ratio. What pistons should I use. Looking at TRW L2465 with .215 dome or Trw kh426 with .100 dome. There's also a set on ebay trw's with .200 dome.

I scaled out the combution camber. Looks like the 781 will cc smaller. Today I'm going to try to buy the stuff to cc the heads.

Maby I can make the engine run without acting like something is choking it above 3500 rpms.

dan

BOATING ON A BUDGET

hey i have one good cylinder head that is gone through that you can possibly use i will sell it cheap.
I live in MI e-mail me [email protected]
86 454

danielthelen

I cc the heads last night. I use a veterinary syringe and a 1/4 piece of Lexan. I was getting 118 to 120cc. The 120 cc wasn’t necessary the 049 head. Looks like they would be close enough to run on the same engine.

What comperssion ratio should I run? I don't want to have to run Premuim fuel all the time. What Pistion's would it take to make the the proper comperssion ratio? I also need it to stay cool with stock cooling system.


Thanks

Dan