michaelb63

looking to build a 350 to 400hp there is a link on chevy high performance (hot hot hot part one ) build ,vortec heads and intake show only 4 bolts on the intake.mine has 8 is there a diffrence on these mine is a 1992

sprink58

There are 8...the photo mis represents by showing only 4.

johnfharding

There are three versions of small block manifolds. The early 1955 through 1980 something I think it was 1987. Then there is the 1987 through 1996. Then there is the 4 bolt per side Vortec. they are different and they won't interchange generally speaking.

The Vortec heads require a vortec manifold if your looking for a bolt together situation. Likewise the 86 and earlier require there bolt pattern and the middle the same. Some say you can tweak on the middle ones and make them work on the early engines but save yourself the trouble.

johnfharding

In an 1992 you should have the 87 to 95 ish style heads, the difference is the center two bolts are straight up and down 90 degree's to the world where as the others are angled out from the center and are 90 degrees to the head/intake gasket surface.

johnfharding

Boats didn't always follow the car industry on heads etc ,, they usually ran a year or two behind so you would have to double check everything anyone tells you with part numbers and visual comparison.

dereknkathy

the middle heads are a waste of time. flow no better than 462624 or 882 heads. and 624's love to crack. get vortecs. you can take a right angle grinder and cut center bolt holes into slots on the intakes to use middle era heads with early intakes. butcher-looking but works. the only reason to do this is cuz your intakes on your 87 boat rotted out and you had old style ones laying around. don't ask me how i know this...i will take the 5th. THEY SAY you can modify vortecs to take early intakes, but you hafta plug orig holes with bolts that are same hardness as head, grind them flush with head intake surface, and then re drill to old style angle. and there is not much meat to drill-tap 8 center holes. there are lots of 906 vortec heads out there. don't bother with 2.02 valves. get edelbrock RPM vortec or equiv manifold. cams? i used to use the early 350 LT1 grind, but from what i hear, that is essentially same cam as stock 260 mercruiser cam. there are much better perf marine cams out there. we don't have AS MUCH exhaust problems as big block guys. the stock merc style exhaust will be good to about 400 or so. and that is where 454-502 guys are starting from, not aiming for. but if you go too big on cam, you need much longer distance from exhaust valves to where water mixes with exhaust flow (think primary tube length) or engine will suck water at idle.

michaelb63

so what your saying is my heads are the ones that dont flow very well, so i need to upgrade to the newest version out . go figguer just my luck.guess ill have to go with a aluminum intake too.

dereknkathy

they are no better or worse than-let's call them-gen 1 heads. but harder to find intakes for. the 906 vortecs are a BIG improvement. better than many of the aftermarket performance heads. but if you are looking for 400 hp out of a 350, the vortec head or aluminum aftermarket heads are the first place to look...another thing. every guy who wants to hop his 330 hp 454 up to 400 or more, everybody says "cast crank-cast pistons-2-bolt blocks...won't hold up!!!" i don't hear that said about small blocks. why is that? personally i feel a big block with cast internals would hold up to 1 hp per inch longer than a small block at the same power ratio...

87MagnumII

I built a pretty stout 350 2 years ago. I used a 350 block from a 1997 Chevy truck, 906 vortec heads, gm lt4 hot cam kit, performer rpm intake, forged flat top pistons, stock cast iron crank and rods, but I had the crank balanced. Runs like a raped ape. I turn it to 5200-5400 all the time, smooth as silk My buddy has a 330 hp 454 in the same boat as mine and I can pull him by a few mph. Best I have seen on gps is 63-64 mph. Boat ran 54 with a stock 260 hp merc 350.

michaelb63

mine is a 350 mag didnt the mags come out with forged cranks and rods,the intake is a 14096242 dual plane high rise ,but it looks like it weighs a ton.