FasterPlease

Ok, I'm looking for more sage advice found on this website.

I have found my self needing to re bore a couple of cylinders. They were out of round. YUK.. (nasty blow by) I am currently at 30 over with a set 8.9/1 forged pistons. Since i'm going to the troulble of boring and new pistons, I would like to bump up the compression and change camshafts, springs, etc. I have a set of aluminum bow tie heads with a 115cc chamber. I also have a 4.25 crank that is in great shape. I want to stay on premium pump gas.

Is there a magic combo?

Thanks in advance,
Kyle

Sick Stinger

iTrader: (23)

What block 454?502?talldeck?
-Mike

getrdunn

iTrader: (7)

Is this for a 454? If so and your not going to stroke it I have a set of .040 over mid dome kb pistons. NEW in the box.

FasterPlease

Duh, Good point! It's a gen VI mercury 454 mag. 30 over.

FasterPlease

I'd be interested in those pistons. but it is allready stroked wit a 4.25 crank. Thanks for the offer.

getrdunn

iTrader: (7)

You'll have to do the calculations however I would assume that you'll want to stay with flat top pistons or maybe a small dome (.090-.120) with 115 cc chamber heads.

Where did you want to end up with comp.? 9.3, 9.5 to 1?

Sick Stinger

iTrader: (23)

Im running 9.8

mike tkach

iTrader: (3)

you can safely bore it to .060 over.you can get off the shelf parts for that combination.marine engines with 4.250 stroke make tons of torque,if you use aluminum heads,10 to 1 is safe with 93 premium gas.good luck with your build.

FasterPlease

I'd like to wind up some where under 10:1. I'm starting too look around for the pistons. Just a small bump. I have flat top now. Any cam shaft combo's? This is in a 22 foot Chris Craft XK. '73 model. The hull is not nearly as efficient as todays designs but that is half the fun to clean a baja's clock. I'm using a Bravo X 1:65 and swinging a lab 26p bravo 1. But.. that was with cast vortech heads and smaller cam shaft. I hope to be able to step up to at least a 28 prop. I don't want to sacrifice to much out of the hole.

Thanks,
Kyle

Raylar

First thing you should do is find a really good machine shop with great equipment and somewhat knowledge in marine endurance engine builds, stay away from shops that only do backyard work or just drag race stuff unless they are really knowledgable on proper block and engine prep. for marine.
There are tons of rotating assembly sales companies out there, just stay with the good (not cheap) parts and you should be fairly successful if you don't skimp or cut corners.
As for hole shot with that drive ratio, that small 22 foot hull and a good 500ft/lb plus torque big block running 9.5-10.0 to 1 compression, your hole shot won't be a problem, however your drive life might be.

Don't go to big on cam selection as bottom and midrange will suffer.

Good Luck

Best Regards,
Ray @ Raylar