Why the overbore from 396 to 402 - Page 2

55chevy · #1 10-23-2003, 05:01 PM

I've seen a few Chevelles that way too. Non-SS cars. I've seen a few 71 402 Heavy Chevy Chevelles with 400 air cleaner decals on the 402. And I've seen a 71 Malibu with a 402 BB that had 400 fender emblems and air cleaner decal.
Probably too many Chiefs going on back then. That's probably why there were so many different things going on at the same time. I'm sure everyones been in that situation. [img]/ubbthreads/images/graemlins/headbang.gif[/img]

**Kurt S** · #2 11-05-2003, 04:52 AM

JoeC got it right. It was emission rules related.

The GM literature (parts books, manuals, etc) got real confusing, calling the BB a 400 alot of the time.

I assume the new block handled the .030 overbore.
Interestingly, the late 69 blocks did not use the 70 3 digit code format, but the late 69 axles did.

**Mr70** · #3 11-05-2003, 06:23 PM

The three letter suffix began on the new 402 CID blocks.
Their cylinders were overbored by .032.
Example:
Code JH is 396.
Code CJH is 402.(or 400 as Kurt mentioned)
I have seen late built 1969 Chevelles with the three letter suffix block.

Kurt S
You say no 1969 Camaros have been found with the three letter suffix,even thought the 1969 Camaro model was carried over late into the 1970 model run.
I would have thought those later built Camaros recieved a three letter suffix,as the Chevelles did.
Anyone know why they didn't?

**Kurt S** · #4 11-05-2003, 07:00 PM

[ QUOTE ]
I would have thought those later built Camaros recieved a three letter suffix,as the Chevelles did.
Anyone know why they didn't?

[/ QUOTE ]

I'd guess cause it was a model year extension and they chose not to change the codes midyear (though it's not really changing them, just adding a digit...).
I've heard of 2 Camaro blocks with the 3 letter code, never seen them.

toner · #5 10-23-2003, 02:09 AM

I seem to remember car insurance cost going higher if the motor was over 400 cubic inch and that the 396 was always closer to 402. [img]/ubbthreads/images/graemlins/confused.gif[/img] So GM said that 402s were 396 to keep below the 400 cubic inch insurance benchmark. But maybe what I heard was just an urban legend. [img]/ubbthreads/images/graemlins/dunno.gif[/img]

toner
p.s. is this pick on charley week? [img]/ubbthreads/images/graemlins/grin.gif[/img]

Dedicated to the Promotion and Preservation of American Muscle Cars, Dealer built Supercars and COPO cars.