Why the overbore from 396 to 402

[JTH74]

I think that Jerry McNeish said in his book that some of the late 69 SS396 Camaros were actually 402's, I will have to go back and read that chapter again just to make sure, I remember him saying that the block casting #'s changed.

[Chevy454]

On the same note, some head changes were made along the way in '69 as well. I found this out by accident, as I bought a set of 840s that had never had valves or seats put in them, but were made for the 1.88 exhuast valve, and tapered plug. On the shelf we had a set of 840s that originally had the 1.72 with flat seat plug...the interesting part is they were cast in the SAME WEEK (in May sometime). So, I had the last of the old style with specs of the new style, just by luck. I called MacNeish and Colvin and they said that was correct, that they did a changeover in May sometime to get ready for the upcoming year, and my 840s were kind of a mix between the old 840s and the new 291s. Some cars ended up with 291 heads on them, and it's probably safe to say some got "funky" 840s like the ones I have.

Some wierd stuff took place back in the day... [img]/ubbthreads/images/graemlins/smirk.gif[/img]

[JoeC]

some late 69 Chevelles have the 402

[55chevy]

[ QUOTE ]
I think the "Malibu 400" was a model name

[/ QUOTE ]
I don't know about that Joe. The one I saw, I'm thinking it was a 71 but it may have been a 70. It was a real light green color, like the sea-mist green that almost looks silverish. It had the malibu interior, malibu dash, I think it had a black vinyl top, but it was factory ordered with a 402bb. Standard orange valve covers.. pretty sure it was an automatic car. 400 decal on air cleaner and the body emblems had Malibu on the fender sides behind the front tire and the slanted 400 emblem on the fenders in front of the wheel opening. There was no doubt about the car, it had a build sheet and everything. Now that I think about it I'm thinking it was a 70.

[55chevy]

[ QUOTE ]
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.

[/ QUOTE ]

Found an example.. This ones a 72
http://www.dealsonwheels.com/search/...-200308-000006

[Kurt S]

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]

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?

[copo9566aa]

Another example...
72 Malibu 400 [img]/ubbthreads/images/graemlins/biggthumpup.gif[/img]

72 Malibu 400

[Kurt S]

[ 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.