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Thread: Are CJ Blocks That Much Better ??

  1. #1
    Hallett19
    I have a cobra jet block, but I want some more info on those babys. Its funny, I have the bad heads and an awesome block, go figure.

  2. #2
    spectras only
    Hallett ,what makes a CJ is the heads ,not the block.The SCJ has a different head altogether as well.I think all 429/460 blocks were cast in Lima ,with different deck heights ,but they're basically the same.The letters inside the block doesn't mean it's a CJ.I'll check my books at home later.In the meantime Mr460 or 058 might chime in with the proper info.Fomoco's offer is pretty good,and I would get forged pistons for that one ,if you'll get it.Later

  3. #3
    RiverDave2
    Shouldn't this be in the "other" forum? Or are we expecting it to turn into a flaming mess shortly... http://free.***boat.net/ubb/wink.gif
    RD

  4. #4
    topless
    A cobra jet has 4 bolt mains. A standard has only 2

  5. #5
    77charger
    Originally posted by topless:
    A cobra jet has 4 bolt mains. A standard has only 2
    true if it is a 2 bolt then its standard.4 bolts are pretty rare.

  6. #6
    spectras only
    Only the 71 Boss,72 HO ,71 CJ and 72-73 4 barrell versions use four bolt mains. Only these blocks are cast to accept four bolt mains.I think Hallet's boat is mid to late seventies.

  7. #7
    058
    Very few CJ blocks are 4 bolted but there were a few. All the SCJ blocks have 4 bolt caps. The only difference in passenger car blocks and CJ blocks is in the crank webbing. All the CJ blocks I've seen have been "machined web" blocks [thicker webbing] and pass. car are usually "cast web" but there are no hard-fast rules here. Mach. web blocks have turned up in trucks, cars and marine and industrial applications. My recommendation is to not worry about a 4 bolt block in jetboat application, the 2 bolt blocks are plenty stout for anything short of high boost/heavy blown use or lots of N2O. The weak link in the chain is the stock rods. Invest your money in a set of aftermarket rods, it will pay bigger dividends over a 4 bolt block in the long run.

  8. #8
    77charger
    Originally posted by 058:
    The weak link in the chain is the stock rods. Invest your money in a set of aftermarket rods, it will pay bigger dividends over a 4 bolt block in the long run.
    actually the truck rods are the same as the cj rods you can tell by the rod bolt heads.
    (was reading from my ford performance book.I my self run the car rods(non scj)and have no prob with them at 5500 rpm.

  9. #9
    058
    I have run the stock rods too and never had a failure but that doesn't mean it can't happen. I start thinking about those stock rods in my engine at 6800 rpm and it starts makin' me nervous. I now run a set of Crower steel rods to 7200+.... I sleep better at nite now.

  10. #10
    Hallett19
    058, what are you runnin and at how fast ? arent jets pretty much in-efficient at the many R's ?

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