So I just need some clarification on a couple of things. The engine that we want to swap to the firebird comes from a 3rd gen Formula with the 350 TPI which we are converting to carb. Now I know that engine has a 2 bolt main vs a 4 bolt main. We would like to see around 450-550 HP on spray or NA, which is going to hold up longer? We are also going to stroke the engine to a 383. Any help would be appreciated.

Thanks
Bernie

 

Generally a 2 bolt main will hold up to 600 horse in an N/A application. but for force fed engines i'd use a 4 bolt just to be safe. You'll have to worry more about throwing a rod or blowing a hole in the piston before you loose the crank to a broken main cap.

 

Either one would be fine. The condition of the block is more important than how many bolts are holding the main caps on.

 

if you really want security start with a 2 bolt and have it tapped to be a splayed four bolt. then put some ARP sutds in there.

 

4 bolt mains tend to crack easier... if you look at where the extra bolts go in, it is putting to much pressure on the weakest spot. Best bet is splayed 4 bolt, which repositions the outer bolts. For the power you are trying for I would splay the outer bolts to be on the safe side, but a 2 bolt should be more than sufficiant for you.