View Full Version : 401 V8- Big Block or small block?

02-21-2010, 04:10 PM
i'm trying to determine if the 401 is considered a small block or big block.

does it use the same bellhousing pattern as a 360 / 727?

02-21-2010, 04:14 PM
It s basically the same engine.
Most external things will fit

02-21-2010, 04:21 PM
Considered a small block V8.

02-21-2010, 04:22 PM
X3 on the small block. :thumbsup:

02-21-2010, 04:24 PM

02-21-2010, 04:44 PM
AMC didn't have "small blocks" and "big blocks". They had one block that was machined to the correct sizes. Pontiac was the same (for example).

02-21-2010, 04:53 PM
"M" block for mid-block

02-21-2010, 05:32 PM
I knew this would open a big can of worms. There is a million different opinions out there curious to here the truth.

02-21-2010, 05:53 PM
The term is only relavent to other makes.
AMC had three generations of their V8.
Each generation came in different capacities according to the bore and crank throw, but was based on the same basic design.
So as AMC never had a smaller family of V8's or a bigger one either, the terms are irrelevant.:cool:

02-21-2010, 07:43 PM
Gonna side with ferretjuggler on this one. Correct me if I'm wrong, doesn't the AMC 327 look like a big block in appearance despite not being one?

02-21-2010, 08:00 PM
the gen 1 amc rambler v8s where around the size of a ford/chevy big block. the gen 2/3 amc v8s (290-401)where a mid block, they had the physical size more like a small block but a bore closer to a big block.

02-21-2010, 08:01 PM
I think the term big block is only acceptable when a manufacturer designed a new engine thats only purpose was to be larger than their previous units. Like the Chevy big block and Chrysler B/RB. Not just modified the previous design.

02-21-2010, 08:52 PM
The blue ones were big blocks, the black one were small blocks,
So what color is yours ?

Mike D.

02-21-2010, 09:51 PM

blue mostly:D a little grease left on it.

02-21-2010, 09:52 PM

blue mostly:D a little grease left on it.

Then it is mostly a big block, if you want a small block paint it black :p

02-21-2010, 09:55 PM
The blue ones were big blocks, the black one were small blocks,
So what color is yours ?

Mike D.

Mike is right, and the reds ones are the dodge 318/360 design. :whistle:

02-21-2010, 10:04 PM
This past year I got into IHC trucks. I have one with the IHC 345 and was parked next to one with the AMC 401. The 401 is definately smaller!

As far as big or small block AMC did not do that, they had one block size but the internals were different.

Mark Wilde
02-22-2010, 12:06 AM
The year of the rig dictated what color the motor was. Earlier were blue, later were black. They are the same size motor though. I'll have to side with everyone that says there really is no "big" or "small" in the AMC world. The 360 is the same size block, externally, as the 401.

And to answer your second question, yes, a 401 is the same bolt pattern as a 360. There's a couple things you have to do to it to match a 401 up to a TF727, but it's all minor. It's basically take out the 360, change the flexplate to a 401-specific, remove the crank bushing, throw that sucker in (gently!) and away you go. :fsj: I've done it, as have many others.

02-22-2010, 05:27 AM
Don't forget about the red blocks too...

My AMX's 401 came out of a IH school bus and was red.

02-22-2010, 11:12 AM
For the last generation of AMC V8 :
- rather a small block according to the exterior dimensions
- but the bore spacing of 4,75" is larger than the bore spacing of a Chevy SB..

02-22-2010, 12:49 PM
I was told, when building an AMC to think of it as a Medium block :confused:

I was told to spec the build right in between what you would a Small block & Big block . . .

As goofy as it sound there was always parts spec for right in the middle of what you would have of used in a BB v.s. SB . . . ;)