I'm going to look at an old truck that supposedly has a 400cid small block chevy under the hood. If I remember right, you could identify the 400 block because it had an extra freeze plug on each side. Seems like a smaller small block had 2 freeze plugs vs 3 on the 400. Or was it 3 vs 4? Help appreciated. I'll probably buy it anyway, but I'd like to know what I'm looking at.

 

The freeze plugs are the same number but a good way to tell is that on a 400, the freeze plugs are offset....one is toward the bottom on the block instead of in the middle.

 

Another way to id a 400, is that its externally balanced, and the harmonic balance will have a big chunk missing out of it and there will be a counterwieght on the flex plate.

 

I do remember the externally balanced bit. All other small blocks are internally balanced. Didn't know it was that easy to spot on the balancer. Thanks.

 

easiest way isthe block around the freeze plugs stick out the have i guess you call a hump around the block 2 humps usually meant 2 bolt 3 meant 4 bolt
but not always
casting number
330817..... 400...72-80...2


3951509....400...70-71...4
3951509....400...74-80...2
hope this helps
Ed

 

330817 73-76 Passenger, 75-80 Trucks 2 bolt main + 3 freeze plugs
3951509 73-76 Passenger, 75-80 Trucks 2 bolt main + 2 freeze plugs
3951511 330817 73-76 Passenger, 75-80 Trucks 4 bolt main + 3 freeze
plugs

 

Where is the casting # located? Thanks.

 

the dipstick is on the drivers side, correct me if i'm wrong.

 

so is a 350

 

Unless is an ext. balanced 383. You will see the last 3 digits on the block.