My car is in the shop right now but they havent gotten to it quit yet. I have a 1986 Trans Am WS6 with the LB9 305 TPI. My uncle who used to own the car and the pontiac dealer both said that it was a 4 bolt main block. Is that true? The guy at the shop said he has never seen a 305 4 bolt. I am asking him to put in one anyhow even if its not. He's charging me an extra $100 to do so. Does any of this sound right?? Any advice would be great!




Project_1986_TA

 

There's never been a 305 4 bolt from the factory ever. Are you making close to 500hp with that 305? There's no real need for a 4 bolt main with a 305.

 

What about my new 350 im putting in? I told him to put in a 4 bolt anyhow. It will only have around 275-280HP for now. My dad and uncle seem to think it would be more sturdy with a 4 bolt.

 

It certainly wouldn't matter as far as putting the engine in the car whether it was a 2-bolt or 4-bolt 350 block.

Opinions vary on the relative merits of factory 2- and 4-bolt blocks. 4-bolts probably help keep the caps from squirming, but the way the factory did it actually weakened the main bearing web.

Splayed 4-bolt caps, using a 2-bolt block from the factory, is the stronger setup. But, how many years were 2-bolt small-journal SBCs hot-rodded before 4-bolts came out in 1968? Your intended use is safe for 2-bolts, to be sure. You won't hurt a 4-bolt, either.