[dodgemonaco68]

i have a 1976 malibu with a 350 2 bolt main and a TH350 auto,. i had just heard of a 400 motor for cheap,. i have not been able to see it to know if it is a BB400 or not or the year yet,. but was wondering what differences i may encounter with switching the motors or if it would be easier bolting up a 2 bolt main motor as opposed to a 4 bolt main and keeping the TH350 tranny for the time being. thanks!
alex

[454me]

They are the same motor as far as installing them goes. The only real difference is the bore and stroke is different on the 400. The 2 bolt or 4 bolt main is refering to the number of bolts holding the main caps for the crank inside the motor. If your doing a motor swap its a simple change. If its a BB it would be a 396 or 402 in that area of size. It will require more changes. A big block change would require most likely heavier front springs, different motor mounts, different exhaust,bigger radiator, different brackets for alt,ps. And I probably left out a few.

[Blazin72]

The 400 Chevy will drop in place of the 350 without any problems. It's difficult to tell what size a small block is just by looking at it because the Gen Is are pretty much the same on the outside. Some 400s had three freeze plugs on each side of the block while other 400s had two just like the other small blocks. If you get a chance, look at the casting number on the drivers side of the bellhousing flange at the back of the block. Look that number up and it'll tell you what you have.

[MI2600]

The difference is about 50 cubic inches.

You can tell a 350 from a 400 by the balancer. The 350 has a consistent outer edge. The 400 has a scalloped edge.

[dodgemonaco68]

making sure the motor would bolt up was my biggest concern, and i really doubt this motor would be a 396 or a 402 so it sounds like this will work out good. i'll check the numbers just to make sure,.. thanks guys !
Alex

[jimfulco]

If it's a small-block 400, the flywheel's different (400 wheel has a counterweight).

[Chopt 48]

As M126000 and Jimfulco said, If they are both small blocks the 350 is internally balanced and the 400 is externally balanced. The 400 will have a counterweight section in the vibration dampener and a counter weight on the front side of the flywheel. The other major difference is that the 400 small blocks have Siamese cylinders (the cylinder walls are connected in the water jacket. There are two steam holes between each pair of cylinders in both the block and heads on 400's.
As long as you get those two parts with the 400 it is a bolt in swap. The trans should hold up to all but extreme abuse.
The 400 BIG block that you are alluding to is a different animal. And will take all big block brackets. I think you are referring to the 396 / 402 engines.

The visual differences between small and big block Chevy engines are very easy to recognize and you should have no trouble telling if it is a big or small block. The big block exhaust ports are evenly spaced while small block engines have the two middle ports close together. Also the big block rocker covers are quite a bit larger than small block covers.