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Chevy 402

Buche

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Buche Enthusiast

Buche

Posted
Posted

Hello again, its been some time since i have posted but im back and with a question! my question what can a 402 be taken to? i heard that all it is is a 396 with a bigger bore but im coming here cause i know a lot of you will know! the reason i ask is because i just got one for free it does not run but it is in good shape to rebuild and im thinking about dropping it in my 68 if thing that you can give me will help out a lot, thank you much!

 

 

Bobby

Mike G Enthusiast

Mike G

Posted
Posted

You will want to take it to a machine shop and have it sonic checked for weaknesses. If they find none, generally a safe .030 is standard and you can generally go as big as .060 over. You may want to shop for parts before you start taking that down and find out it will cost you more than a few body parts to build.

--Mike

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted
You will want to take it to a machine shop and have it sonic checked for weaknesses. If they find none, generally a safe .030 is standard and you can generally go as big as .060 over. You may want to shop for parts before you start taking that down and find out it will cost you more than a few body parts to build.

--Mike

 

If I understand the tale about 396-402, the 402 is already a .030 overbored 396. Going another .030 would be like taking a 396 and boring .060 oversize. Not sure I would trust a .060 overbore on just about any gas engine from that time period.

GMstrong Enthusiast

GMstrong

Posted
Posted

Yea i agree with mike take it to a machine shop tell him you want it .60 over and im sure he'll tell you if its safe or if it will be unstable.Im sure it will be possible.

  • 1 month later...
CodyLee New Member

CodyLee

Posted
Posted

The 402 is not a bored 396...From what research Ive done, the crank and rods are just a little different to allow more stroke, which gives the added displacement. I had a 402 a couple years ago. I took it to a machine shop and the machinist told me that if the block was strong, we could go as high as a 468 or in that immediate area, and if wanted to get really wild, we could stroke it as well with a 427 crank. He said it was a very versitile motor with many options. However money comes to play as well Just my .02

ChevyTech77 Senior Enthusiast

ChevyTech77

Posted
Posted

The 402's were a factory F up of the 396. They are in fact, .030" over bored 396 blocks. I have taken early 70's big blocks to .100" over many, many times without issue for street and race applications.

Blee Enthusiast

Blee

Posted
Posted

You're exactly right. The 396, 402 and 427 all used the 3.76" stroke crank with different bore sizes. The 402 block needs to be sonic checked to see how much meat is in the cylinders so you'll know how much it can be bored. Chevy recommends a minimum wall thickness at 1" down in the bore of .090 and .125 is more desireable. I've heard not much more than .060 can be expected. No way are you gonna get 468 cu in out of an original 402 block, more like 408. If someone wants a big inch motor just find a 454 block with a bigger bore. You can safely bore one of those .100 over and make a 475 cu in motor using the 4.00" stroke crank.

 

The 402's were a factory F up of the 396. They are in fact, .030" over bored 396 blocks. I have taken early 70's big blocks to .100" over many, many times without issue for street and race applications.
Blee Enthusiast

Blee

Posted
Posted

And another thought if you like to mix and match BBC parts. You can use the 4.00" stroke crank in the smaller bore (4.125") 402 block (with some block mods) and the 6.135" rods and get anywhere from 427 to 440 cu in depending on the bore size. I've heard these motors really have a lot of torque. I'm thinking about building one for my 57 since I have all of those parts except the pistons laying around.

 

You're exactly right. The 396, 402 and 427 all used the 3.76" stroke crank with different bore sizes. The 402 block needs to be sonic checked to see how much meat is in the cylinders so you'll know how much it can be bored. Chevy recommends a minimum wall thickness at 1" down in the bore of .090 and .125 is more desireable. I've heard not much more than .060 can be expected. No way are you gonna get 468 cu in out of an original 402 block, more like 408. If someone wants a big inch motor just find a 454 block with a bigger bore. You can safely bore one of those .100 over and make a 475 cu in motor using the 4.00" stroke crank.

 

The 402's were a factory F up of the 396. They are in fact, .030" over bored 396 blocks. I have taken early 70's big blocks to .100" over many, many times without issue for street and race applications.

 

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