How do you tell the difference between 2 and 4 bolt 350 sbc without opening the engine? I have already ran the block casting numbers and they tell me that it could be either. So how do i tell without dropping the oil pan or taking the engine apart.

 

you can't if it says it could be either

 

What he said.

The factory uses the same block casting in different applications; and installs whichever caps go with the application.

If the block stamping code is still on it, look at that; it'll be something like V{3digits}{2 or 3 letters} If the first of the letters at the end is "T", then it's a truck block, and it has better odds of having had 4-bolt caps installed on it. If not, then it almost certainly doesn't.

It makes little or no difference however, for the use most of us put a motor to. I sure wouldn't not buy a block just because it's a 2-bolt, or pay extra because it's a 4-bolt.

 

I have two 350s sittting in cars and i just wanted to know if i had a 4 bolt so i could rebuild that one instead of the two i have as a short block now. Thanks for the info.

 

I have a feeling (and what few numbers I have so far back this up) that the suffix code will tell you whether it's a 2 or 4 bolt main.

The whole 2/4 bolt issue is really blown out of proportion, but the fact remains GM thought it was important enough for the additional expense in many applications. If they felt it was important enough for the expense, I would surely expect it to be reflected in something. There is no *factory* literature around that explains the 2/4 bolt difference/reasoning, just like the 010/020 casting ID "high nickel" myth that is unproven.

In any case, a truck block seems to be about 95% likely to have 4 bolt mains. The suffix code will tell you the original application. I even started a (very) small list of which suffix codes were "known" to be two or four bolt, but it is very incomplete, and until at LEAST two of every code have been verified, it's not even close to being authoritative.

suffix code "listing" Gotta update my email address listed there though.