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Thread: BBC 402 questions

  1. #1
    Senior Member
    Join Date
    Oct 2009
    Posts
    131
    Hey guys- I have a chance to pick up a virgin 1972 402 bbc, and was wondering about the potential of this motor for a jet boat- I don't have any casting numbers yet, but it is DIRT cheap, and complete, and runs. What kind of power will this make? Can I drop a 427 crank in it? Are there any oiling issues with these motors I should know about, like the BBO? Opinions and comments are welcome, both good and bad. Thanks, Stan

  2. #2
    Jet City
    The 396 and 427 use the same crank stroke, you'd put the 396 crank in a 454 block for a 427 (4.25 bore x 3.76 stroke). I'd think a 396 could be a fun jet power plant, and yes, the factory oiling systems are great.

  3. #3
    Jet Boat John
    Stan, 402's are .030" over from the factory 396's. You can install a 427 crankshaft but you won't gain anything as it's the same stroke as what you have at 3.75". The difference is in the bore, the 402 is 4.125". The larger 427 and 454 motors have a 4.250" bore. You probably can't bore your 402 out a 427, and that is the reason 396's and 402's are priced less than 454's. Funny though 454's are alot more common and parts are cheaper!
    402's came with "big" oval ports but they used what is called a "simi-closed" chamber head, it's chamber is large and flat and not normally thought of as a performance head.
    If your set on swapping cranks to gain cubes you can install a 454 crankshaft with it's 4.00" stroke into your small bore big block by using Keith Black piston KB361, you will need an external balanced flywheel and damper from a 454, the result will be a 434cid.
    JBJ

  4. #4
    mickeyfinn
    They make decent power and are a good engine. Been running one in my v-drive for many years. The last rebuild lasted 8 seasons running it hard and putting a lot of hours on it. Buy it up. You may not be the fastest on the lake but you will be there more often than most.

  5. #5
    GofastRacer
    The 402 is a .030 over 396, the block is like any other big block, same oiling!. Same stroke as 427, to put a 454 crank in it you need to grind the bottom of the cylinders for rod clearance!. It was put out in 4 different configuations but the exeption would be the L-78 which is the same as the Corvete L-78 396 except for the bore size!..The oval port heads that came with those are a good head, they are a semi open chamber, put the big valves in and do a clean up and they will make excelent power!..For a run of the mill jet boat it will work perfectly!..

  6. #6
    396_Z
    The BBC 402 is probably one of the most overlooked of the family. I personally love mine. The 71-72 402 head is a large oval port, semi-closed chamber so it tolerates higher compression rather well and still flows better then most stock 454 heads. TRW/SpeedPro makes several different pistons for them including the approx. 10.2:1 comp forged ones that I have. (part # 2242F IIRC. I could go look at the box if you wanted.)
    If you want a fun, reliable and upgradeable engine then snatch it up. If you want power at all costs then it's probably not right for you.
    As a side note, I've had 3 396's and 2 402's now. All of them in performance car applications. For some odd reason that escapes me I've been able to hand more 454's their repective asses then I've lost to. Why? I can't say but something in the combination works.
    EDIT, If you want pics of the heads to see what the ports and chambers look like I have mine sitting out in the garage. I don't know if it would do you any good in you decision or to help you understand a semi-closed chamber but I thought I'd offer.

  7. #7
    canuck1
    I'll buy it for a resto I'm doing, if you pass

  8. #8
    Senior Member
    Join Date
    Oct 2009
    Posts
    131
    Thanks for the replies, guys- I brought it home- Here are the numbers-Block-3999290 (72 240hp truck) heads 6272292, intake 6288768(I think!)- Looks to be all original and unmolested, but it won't turn with a breaker bar , so it's gonna get pulled apart- He told me it ran, but for $50 I guess I can't bitch!
    Thanks again, Stan

  9. #9
    Norseman
    Thanks for the replies, guys- I brought it home- Here are the numbers-Block-3999290 (72 240hp truck) heads 6272292, intake 6288768(I think!)- Looks to be all original and unmolested, but it won't turn with a breaker bar , so it's gonna get pulled apart- He told me it ran, but for $50 I guess I can't bitch!
    Thanks again, Stan
    Stan;
    You can't go wrong for that kind of money!!
    Bob

  10. #10
    Moneypitt
    396 Z, the reason the 396/402 combos work is the shorter stroke. Which allows them to get Rs quicker than the 454. The 54 will eventually go on by if ran long enough, but for a short spurt the smaller motor kicks ass..........MP

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