I have an opportunity to get a chevy 400 with a 400 turbo trans real cheap and I'm not sure if it's a big small block or a small big block. Are parts for these as common/cheap as say a 350? will the 400 turbo bolt up to a 350?

 

a 400 is a small block. it has all the same bolt holes as a 305, 350 ect.... you can bolt up everything that is on you 305 or 350 to a 400.

 

The 400 is a SBC. GM produced a 396 BBC. When they factory bored it out +.030 in some trucks it was badged as a 400 but was really a 402 BBC. Very rarely will you see a BBC chev classified as a 400.

All Chev blocks big and small use the same bellhousing bolt pattern. Buick/Olds/Pontiac/Caddy use a different bolt pattern (BOP)

A 400 SBC is externally the same as any other SBC so all the aftermarket parts are interchangable. The 400 is the only SBC that's externally balanced so a special flexplate/flywheel and halancer are required.

To use a TH400 tranny you're supposed to use a different flexplate. The torque converter mounting bolts are in a different position than and other GM tranny. The good thing is that a TH350 torque converter will slide right in to a TH400. This allows you to use a common torque converter and flexplate. The other option is to buy an aftermarket flexplate that has the dual bolt pattern for both torque converters.

You'll also need a slip yoke for the TH400. The TH400 has a larger output shaft than any other GM tranny.

 

Count the number of bolts that hold EACH valve cover on.

Four bolts equal a small-block.

Seven bolts equal a big-block.

There are other major differences but this is the easiest way to tell for someone not used to looking at a big-block.

jms

 

I've seen quite a few factory 400 big blocks with TH400's behind them.

I'd recommend checking it to be sure what you've got before considering installation into a 3rd gen.

 

In 70 & 71, you could buy a full-size car that said "400" on the side. If it was a "400 2-barrel", it was a small block (402 CID actually), and came with single exhaust. If it was a "400 4-barrel", it was a big block (also 402 CID), and had dual exhaust. The "400 2-barrel" came with a Turbo 350 and the "400 4-barrel" came with a Turbo 400.

Of course, there's no telling what has happened to any of those things since then; they all interchange freely. A T-350 to T-400 swap is almost a direct bolt-in, and either trans bolts equally well to either any small block or any big block, so we all used to change them at will. This is of course assuming they are both Chevrolet case transmissions.

Do what jms said, it's quick and easy. Then come back and tell us what it really is, and maybe we can help you decide what to do.

 

Both the SBC and BBC had 4.125" bore, but the SBC had a 3.75" stroke, while the BBC had 3.76". So, the SBC was closer to 401 cubes (400.92) and the BBC 402 (401.99).

 

It's a big block.

 

hehe, if your not going to grab it think you could share some info on it? I could use another BBC for my next project if the price is right.

 

Now start getting some numbers off the engine.
Block and head casting numbers.
Engine suffix numbers. They'll be stamped on the pad in front of the right hand head and stamped on the pad above the timing cover. That will tell you what the engine originally came from.