Making a 427 BB

[terry b]

I have a 1971 Chevy 402 BB. I think I read somewhere you could change the crank rotating assembly with a 454 and make it the same bore and stroke as a passenger car 427. Not the long stroke truck motor. Does this sound right?

[Alex V.]

I believe bore/stroke was the same between the car and truck 427's, deck height was the difference. But this should answer your bigger question: http://www.chevelles.com/forums/18-e...nto-427-a.html

[Captainfab]

Installing a 366,396,402/427 crank (3.75" stroke) into a 454 block will give you a 427. A truck 427 (tall deck) crank is interchangeable with a passenger engine crank. It is the same stroke. The 366,427 truck cranks will likely be forged.

Originally Posted by terry b

I have a 1971 Chevy 402 BB. I think I read somewhere you could change the crank rotating assembly with a 454 and make it the same bore and stroke as a passenger car 427. Not the long stroke truck motor. Does this sound right?

[b454rat]

If you take a 454 crank and put it in 396/402 block I believe it's a 427 stroker. But think you need to clearance the block to clear the 454s crank throw. Get a 427 truck motor and put .400" longer rods and car 427 pistons for a 427 long rod. Or with a 454 crank/pistons, and slightly longer rods(can't remember length) for a long rod 454....

[Stickweld]

I can tell you for certain that it is simple to make a 396/402 into a 427 as I have been running one in my 68 camaro for 25 years now. You can use a standard 396/402 crank in a standard deck height 454 car/pick-up block with the regular length passenger BB con rods and 427 car pistons. Nothing trick or modified required. You do need to use the flywheel and harmonic balancer off the 396/402 because the 454 crank is externally balanced and therefore uses a different balancer and flywheel. The 427 safely revs higher than a 454 with the same parts and costs just slighly more than rebulding the 396/402, because 427 pistons seem to be bit priced a bit higher than the others.

[nikwho]

A 396 has a std. bore of 4.094. A 454 crank stroke is 4". This would net 421.25 cubic inches. If you went +0.030" on the bore at 4.124", you'd get 427". Just realized that you were speaking of a 402, not a 396. So, I believe that the 402's have a factory bore of 4.125", so, that'd put you at 427". Though, a standard deck height 427" BBC has a 4.25" bore (same as 454) and a 3.76" stroke crank.

So, while you can make a 427 out of a 402 or 396 block, you can not make it the same bore and stroke as a passenger car 427 by stroking it. You wouldn't be changing the crank.

ETA:
But, as stated above, if you aren't looking to use your 396 block, and choose to use a 454 block, the 454 and 427 have the same bore, with the differences being that the 396/402/427 cranks have 3.76" of throw and the 454's have 4" stroke. Be careful and think about what you're doing, as the 454 is externally balanced and the others are internally balanced. So, you won't be swapping your balancer and flexplate/flywheel. Not successfully, anyway. Whatever you're building, you should have the rotating assembly balanced and understand if you're working with an internally or externally balanced assembly and know that your putting the correct balancer and flexplate/flywheel on it.

I have a 4 bolt main 454 block that has a 3.76" crank, 6.135" rods and 427 pistons. It's bored +0.030, so it displaces 433 cu. in., as any +0.030" 427 would.

[cg285]

Originally Posted by Stickweld

I can tell you for certain that it is simple to make a 396/402 into a 427 as I have been running one in my 68 camaro for 25 years now.

i had a (425hp) 427 in my 68 ss camaro. it was easy. i bought a new short block, heads and valve train from the chevy dealer i worked at. i think i spent less than $600 for everything new.

[Blue Rat]

The way have always know it to be done is 454 block. Put rotating assembly of 3.76 stroke 396 or 402 but use 427 pistons because of 4.250 bore. Piston pin location is different on 427 an 454 piston. Use HB an Flex plate off 3.76 stroke engine.