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I am currently looking at a 1972 Monte Carlo with a 402 engine. I never heard of such an engine; can anyone give me any advice on the reliability, horsepower, and performance of this engine? I don't mind if it is not the original engine, because the car will be used as a daily driver. Any information you can provide on this engine is greatly appreciated! Thanks in advance!
 

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A 402 is a 396 bored .030 over at the factory. I don't kow why but I think for new emission laws. So it is a good engine.

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I thought I read on this site that it was due to core shift in some of the blocks, so they decided to do 'em all at .030 over. Nevertheless IT'S A RAT, and a good one at that.
 

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At least in a chevelle, and most likely for Montes also any 396 from 70 on up is actually a 402. Which as earlier stated is a 396 bored .030 over. Mat

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I'm not sure if this is correct but I don't think the 402 was an .030 block 396. The standard bore for a 396 is 4.094 and a 402 is 4.125. I heard somewhere the reason for the move to 402 CI but can't recall the exact information.

Boring a block because of core shift isn't logical as one would think the condition would result in a block that could not be bored. Plus I don't think GM would produce blocks for 3 years because of one mistake. However I may be wrong.
 

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The best reasons I recall (from a previuos post) were :
1) Could use the same bore tooling as the SB 400 (same size bore)
2) "tighter" emmision standards for engines under 400 CID that a 396 couldn't meet.

There might be something to be said about Chevy not wanting a small block (400 CID) being bigger than a big block (396 CID), but I think if that were the case they wouldn't have continued marketing it as a 396.



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Gene McGill
68 SS396
Team Chevelle Gold #14
 

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Corporate GM limited engine sizes to below 400 cubic inches prior to 1969. GM was making the statement that they "were not into racing." In late 1969 this restriction was lifted, so the 396 became a 402. GM had already spent alot of money on advertising the 396, so they did not publicize the 402.
 

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Hey Todd: check your math!

4.125
-4.094
------
=.031

GM raised it to 402ci due to emissions. This was also the LAST year for closed chamber heads, as the open chamber heads burned cleaner. It seems that emissions and insurance companies changed the face of muscle cars forever.

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Rob Clary
'70 LS-6 Chevelle
Team Chevelle Gold Member #85
Interested in COPOs, Yenkos or other dealer built muscle cars then go here:
ortrackm.missouri.org/~yenko
 

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Hey Chevy454, check this out...


4.094
0.030+
-----
4.124

You have to go over .031 on a 396 standard bore to achieve the standard bore of a 402. A machinist is not going to calculate the amount to bore based on the difference, only the piston diameter and the required clearance.
 

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Here are the specs on the 396 and the 402, according to Chevrolet by the Numbers:

Size Part # Bore Date used

396 3935440 4.094 late'68,early'69

396 3955272 4.094 '69

402 3969854 4.126 late'69,early'70

All 3 of the blocks were produced in 2 or 4 bolt variations. The 440 and 272 blocks had the tall distibutor boss, while the 854 block had the short distributor boss. If you look up the 402 block in the specifications chart, under the Notes column, it states ".030 overbored 396".


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Rob Clary
'70 LS-6 Chevelle
Team Chevelle Gold Member #85
Interested in COPOs, Yenkos or other dealer built muscle cars then go here:
ortrackm.missouri.org/~yenko

[This message has been edited by Chevy454 (edited 06-17-99).]
 

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If anyone needs to ever look up part numbers, I would seriously recommend buying the Chevrolet by the Numbers books, as both of them are full of info, and will answer most if not all of your questions.
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Rob Clary
'70 LS-6 Chevelle
Team Chevelle Gold Member #85
Interested in COPOs, Yenkos or other dealer built muscle cars then go here:
ortrackm.missouri.org/~yenko

[This message has been edited by Chevy454 (edited 06-17-99).]
 
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