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2 bolt or 4 bolt?

Discussion in 'The Garage' started by BigCountryx, Feb 28, 2006.

  1. BigCountryx

    BigCountryx 1/2 ton status

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    How can I find out if my 1990 Blazer came with a 2 bolt or 4 bolt main?
     
  2. readymix

    readymix 3/4 ton status

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    Look up the casting numbers on the Mortec website. SOmetimes they will say 2 or 4 bolt though.

    Or you could just drop the oil pan
     
  3. thedrip

    thedrip 1/2 ton status

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    '90 truck is basically guaranteed to be 2 bolt.
     
  4. HarryH3

    HarryH3 1 ton status Author

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    Yep, you can bet it's a 2-bolt.
     
  5. roadnotca

    roadnotca 3/4 ton status

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    Unless its been replaced, then its a Q of, with what.
     
  6. BigCountryx

    BigCountryx 1/2 ton status

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    Thanks, how inferior is the 2 bolt when compared to the 4 bolt. Are you just more restricted to how much power you should try to develop out of it due to the strength or what? If so, what's the ceiling, power wise, to build a 2 bolt?
     
  7. Thunder

    Thunder 3/4 ton status

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    2 bolts can be built to handle up to 400 hp no problem. But over 350 HP the main caps tend to walk around. This can be cured with studs or splayed mains, billet caps ect.
    4 bolts are better for high performance and high load apps. GM went to the 4 bolts in truck cuz truck engines under high load are very prone to detnotation. That puts a lot of strain on the mains so 4 bolts were needed.
    Stock 4 bolts are only rated up to around 350 HP. GM makes caps that are rated for 450 too. So if you use a 4 bolt in high HP apps you should do some work on the mains also.
    for high performance race or a truck engine under heavy loads use a four bolt
    For basic street/strip and light duty truck & 4X4. A 2 bolt will be fine.
     
  8. sledheadak

    sledheadak 1/2 ton status GMOTM Winner

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    if you keep the rpms under 5500 you should be fine
     
  9. drop the hammer

    drop the hammer 1/2 ton status

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    How bought for an 87. Mine is a fully loaded with the 350 option. I was informed, maybe wrongly that its a 4 bolt. Not that it would bother me that much cuase I dont plan to go to crazy with the engine, but does anyone know what engines in what years where 2 bolt or 4 bolt. Would be much appreiated
     
  10. Indyblazer

    Indyblazer Registered Member

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    Chevy 2 or 4 Bolts ??

    When you get into to building Chevy small blocks for serious HP there are many considerations about engine blocks.

    Generally the Chevy smallblock motor DOES NOT have a weak bottom end. Something else usually breaks before the crank assembly, even on a 2 bolt main.
    I had a friend that run an 1/8 mile with Supercharged Alcohol/Nitrous small block chevy motor. He used 2 bolt main blocks. He broke lots of pistons and bent a lot of valves and rods and blasted a few rods through the sides of the blocks, but NEVER broke a crank assembly.

    On the pre-1987, the 2 bolt main motor block was thicker at the webbing under the crank, than the 4 bolt main. So some engine builders sought those blocks and had them machined for after market "splayed" caps.

    ALso, on the pre-1987 blocks there were "4 bolt casting numbers". This casting MAY OR MAY NOT be a 4 bolt main. The casting number tells you only that this was the casting that they used for the 4 bolt main --- Not that it actually was machined for the 4 bolt caps.

    The best method for determining 2 or 4 bolt main caps is to drop the pan and LOOK :eek1: .
     
  11. 1985_K5_Silverado

    1985_K5_Silverado 1/2 ton status

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    Pull the pan, absolutely. Look at this list, it's clear as mud which blocks had 4-bolt main caps (with a few exceptions):

    http://www.nastyz28.com/sbchevy/sblock.html
     

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