396/402 - Team Camaro Tech
Tech 2001 General Tech questions from 2001
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post #1 of 7 (permalink) Old Nov 20th, 01, 01:22 PM Thread Starter
Join Date: Nov 2001
Location: Frankfort, KY USA
Posts: 4

This question has probably been asked a hundred times but could some on explain the difference between a 396 and a 402. I'm looking at a 71 camaro that the owner says is a 402 and my book says 396. Thanks in advance for your help
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post #2 of 7 (permalink) Old Nov 20th, 01, 01:33 PM
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Location: Huntington Beach
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The bore on a 396 is 4.096 , the bore on a 402 is 4.125. A 402 is a 396 bored .030 over. Same stroke...thatís about it.

'69 Z28 (X77 D80 72 72)
302, GM Crossram, Doug Nash 5 speed, 3.42's
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post #3 of 7 (permalink) Old Nov 20th, 01, 03:37 PM
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Location: Columbia, SC
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The story I heard was in the early 70's, GM had some bad castings with the 396 and had to bore them .030 over to clean it up -- thats why they call them 396's while they were actually 402's.

[This message has been edited by Turbo_Jet (edited 11-20-2001).]
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post #4 of 7 (permalink) Old Nov 20th, 01, 03:41 PM
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OK JohnZ, What's the real scoop? Why a .030" overbore?
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post #5 of 7 (permalink) Old Nov 21st, 01, 08:32 AM
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I thought the .30 overbore to a 396 helped to unshroud the valves and made it easier for the 396 to meet emission standards for 1970.....

'69 SS 396/375hp L78 M21 3.73 Fathom green/medium green interior

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post #6 of 7 (permalink) Old Nov 21st, 01, 08:40 AM
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It's related to emmissions requirements. After 1969 (70 model year) engines displacing greater than 400 cubic inches had to meet less stringent emmissions requirements. I guess the theory was that the larger displacement engines were typically used in trucks which have always had different federal requirements for everything from 5 mph bumpers to emmissions.

Mark Canning
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post #7 of 7 (permalink) Old Nov 21st, 01, 12:36 PM
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Actually I think it was because prior to 1970 GM had a policy that prohibited any engine of 400 cubic inches or more from being factory installed in intermediate cars (Chevelle, Camaro etc). That policy was dropped in 1970. So the 396 block was overbored and that resulted in 402 CID. But marketing knew that the popularity of the SS would be hurt, so they kept the 396 designation.
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