Allright i'm buying an 350 off of the local junkyard and i have the choice of a 4 bolt and a 2 bolt main? What is the difference if there is one? I'm going to tear it down and rebuild it. I was planning on getting just a regualr 4 bolt main but i'm not for sure which would be better. I'm only looking to squeeze about 300-350 hp out of it so it isn't goint to be a monster.

 

350 hp max there is no real differance, i'd look for a one piece crank seal and a roller block before i would a 4 bolt main

 

For stock or slightly above, a two bolt is fine, especially if you have the rotating assembly balanced and blueprinted. For up to 600 or 650HP 4 bolt is needed, and if you are going above that, I would get a two bolt and then put splayed 4 bolt caps on it for added strength. But like ede said, I would look for a 1 piece seal roller block before a 4 bolt for that kind of power

 

While you're hunting, see if your project block has an "010" cast into the front wall. More nickel is better than plain gray iron, and the mains question was already answered astutely by F2fast. A two-bolt can be made into a better 4-bolt than a factory 4-bolt.

 

Vader is right. The infamous 39700010 casting is better because of the high nickel content. It was introduced in 67 and was made until 79(i think this was the last year). It was available in a 2 bolt or a 4 bolt depending on what it came in. It was used as a 327 and a 350 block, as they are the same just with different strokes. THey came in everything from Camaros to Vettes to trucks to passanger cars, so it should be very easy to find one in a bone yard. I have two engines that I have built using them, one a two bolt and that is pushing 435HP, and one was a two bolt that is now a 4 bolt splayed. That engine is not finished yet, but will make around 800hp. I found them both in junk yards and just had them machined. They are the best way to go for the money and availability.