refreshing the twins (454's)
 

I dont know a great lot about big blocks or chevy in general as Im a Ford guy. My twins are from a 1995 donor. They run great, dont smoke, and have about 275 hrs on them. I dont want to change the bottom end, but i dont know what size heads to put on? I want an aluminum head and intake, nothing crazy...just looking to shave some weight and add a little hp. So i need some suggestions? I think my motors are 330's so if i could get 400hp, thatd be nice. The engines already have full headers. Boat stays in fresh water too. Thanks.

It can be done, but you will have to be smart about it. The 330 is a 2 bolt block with a cast crank and small rods. That bottom end just really isn't conducive to a lot of hp or revs. I was talking to another member today about a planned build with the same motor. The nice thing about alum.,heads is that you can up the compression without upping the octane. The bad news is that the bottom end is weak... your going to have to do the cam with one that does its magic below 5k with a corresponding intake system and make sure everything works together well. There are a bunch of threads on the subject if you search, 330 on roids etc.

I will be going alum. heads plus a decent crank and rods. The crank and rods from a 454 mag or 502 make decent donors of you dont go crazy.

oso member tunnelvision just put 2 sets of edelbrock heads in the swap shop yesterday,i can vouch that these heads are like new with top quality parts.these heads would really help to wake up those 330s you are giong to rebuild.

The heads Mike mentioned would probably work well with a pair of the ZZ502 cams from a take-out, which would allow you to retain the stock roller lifter arrangement if they are Gen VI blocks. The downside to this cam is that the 110* LSA would probably mean you would have to upgrade the exhaust to prevent reversion, although there was a guy here on OSO who ran that cam with stock Merc exhaust without issues. As the saying goes, YMMV, and the cost of the exhaust might be the dealbreaker for you. However, to take advantage of any aftermarket head with better exhaust flow (the weakest area of the stock heads) would probably mean an exhaust upgrade anyway.

If going with new heads, I would highly recommend the AFR 265. These have a relatively modest port volume that works really well with the small displacement engines, but they outflow a stock rectangular port head considerably. Bob Madara would be the guy to contact for a set of these heads - he provided me with a great price for a fully assembled pair of heads with the upgrade inconel exhaust valves. Also, keep in mind that longer pushrods will be required for the majority of aftermarket aluminum heads with the raised exhaust ports, as well as different head bolts. I believe the Brodix Race Rites may keep the ports in the stock location, but not sure what pushrods they require.

Good luck with your build. Most on here, including me, can speak to the fact that these minor "upgrades" rapidly turn into a major infusion of money into your boat. Maybe a more cost effective approach would be to find a good set of higher hp takeouts that you could drop in, and keep your stock motors for backups or for if/when you sell the boat.

Oops, just re-read you post, and see that they are 1995 (Gen V), so stock roller lifter arrangement will not apply. You also have performance exhaust, so that opens up the cam choices. Just remember that the valvetrain component selection is the most important thing to pay attention to to build reliability in a marine engine. Do not skimp in this area.

budman,is your engine build ready to run yet?sorry for derailing the post.

Real close, Mike. Long block is together, after taking two steps backward to reseal all the head studs. Intake manifold is on, going to prime it this week and dress it out. Then need to finish welding up my startup cart and get it dropped on there. Had to do tax fun the last couple days. Broke now. :(

Not all 330 HP motors are 2 bolt mains. The Gen VI's I've seen were 4 bolt.

THats good to know since I have a gen 6, that would be a bonus.... Any way to know for sure without dropping the pan??

I'm too busy to do a search right now, but I am almost positive that GM went to 4-bolt mains with both the Gen V and Gen VI. You can probably get a definitive answer by Googling it. I don't think the 2-bolt versus 4-bolt deal is the issue with the 7.4L. It is mainly the smaller rod bolts and weaker rods. Also the cast pistons don't do you any good if you run into detonation.