Hi all, Looking for some advice on an engine. I am clearly aware that 4 bolt main engines are better. I am wondering if a two bolt main bottom end will support 450 horsepower. Also, is a 1995 310 or 330 horse a four bolt main or two bolt main??

a 2 bolt main will support 450 hp for short periods of WOT if it has a steel crank. I wouldn't recommend trying 450 with a cast crank though. The 330 should be a 4 bolt main block.

Lined honed and ARP studded block will handle 600 or so. Make sure its balanced real good and clearances are spot on. The 95 should be a four bolt, some of the earlier mark 4 330's were 2 bolt. Cast crank is fine if you keep the rpms below 5200 and everything is blueprinted.

The boat I am looking at has what I believe to be a gen 5 engine. I would like to see about 450 hp but would not run wot hardly ever.

check out The thread "horsepower happy" I built a 91 330 hp to about 425. It seems to run strong. Ron

I thought all gen5's were 4 bolt.

If you want some peace of mind throw some 4 bolt 'retro' caps on it. I've seen them for <$100. My machine shop talked me out of it this time, but I'll probably do it next time... if I get that forged 496 stroker crank

According to Dennis Moore, do not hesitate to use the 2 bolt main block on anything with less than 600 hp and turning less than 6000 rpm.

Formula31 has pretty much hit it on the head. Back in the mid 1980's a few of my friends used 2-bolt main blocks and cast cranks and made 450+hp @5500rpms. They just made sure everything was done correctly, align honed the mains, balanced the rotating assemblies, accurate clearances. Some used bolts and some also used ARP main studs. Studs will give about twice the holding power and are a good idea on a 2-bolt main block for added insurance, but not absolutely necessary. They all survived.

By the way, back then many other offshore boaters and engine enthusiats thought thought we were nuts/crazy for using cast cranks and 2-bolt mains, but like I said they all survived many, many hours with no problems. One particular friend of mine had a twin engine 30' Scarab with two 454's (bored .030") that made about 450+hp each and each had been cut to .010"/.010" on the mains/rods of the CAST cranks he used. He didn't even run engine oil coolers---just 10 quart pans with Valvoline straight 40wt oil----still no problems with either engine. He owned the boat for about 5 years and hundreds of hours after he had the engines rebuilt up until the time he sold it in 1991-1992.