2 bolt main vs a 4 bolt main
 

I am rebulding an older Scarab 30- I bought it with a blown engine (a two bolt main). I am being told that pretty much all the older 70-79 454 330 horse were 2 bolt main blocks. Is this true or do I need to step up to a 4 bolt main? Were earlier Merc 330's two bolt mains? Thanks for any input.

Re: 2 bolt main vs a 4 bolt main
 

All of what I have seen in the low HP 454's have been 2 bolt main. Do you need a 4 bolt? Depends on how much power you are making. It has been my observation that at around 650 to 700HP a 2 bolt block's caps will start to walk. This is on blocks with studs and in drag cars and pull trucks. Since a boat engine is under constant load I would back that up to around 600HP. So as long as you are not planing on going over 600HP then a studded 2 bolt will be just fine. Bolts are fine to around 450 HP.

Chris

Re: 2 bolt main vs a 4 bolt main
 

you can always retro fit the 3 center caps with 4 bolt splayed caps and you ashould be good to go for 800hp. but you might be able to get a good four bolt block for less than the caps and machine work!

Re: 2 bolt main vs a 4 bolt main
 

What cstraub said! For recreational use in the 600 hp at 6000 rpm or less range with a steel crank, good rods, and forged pistons, there is absolutely no reason to avoid the 2-bolt main Mark IV block. --- Jer

Re: 2 bolt main vs a 4 bolt main
 

Scottie, I had several friends (one with a 1979 30' Scarab) who used to use the 2-bolt main blocks all the time back in the 80's for marine use, and we usually used studs, and then we had the main saddles align honed with a good balance job on the crank/rotating assembly----no problems. I even know of a few guys who used them back around 8-10 years ago with superchargers on them for marine applications without any problems.

You should be fine with a 2-bolt block, but it all starts with the shop you are entrusting your stuff to by measuring the block correctly. Of course there are many other things to consider, but if you want it done the right way, then it is very important that you must first pay careful attention to the main saddles, main bearings clearances, and how the crank sits/spins. Have fun.

Re: 2 bolt main vs a 4 bolt main
 

Thank you everyone for your input- I really appreciate it. Scott :D