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2 or 4 bolt mains

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by KILLERK5, Jan 12, 2002.

  1. KILLERK5

    KILLERK5 1/2 ton status

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    I have looked at the TBI engines on SDPC before, but I still dont know the whole story between 2 and 4 bolt mains. I know there is a difference in the number of bolts. Is a two bolt main a good way to go, or should I look around for a four bolt. I have heard both sides, and still dont know which to believe. My engine isnt cutting it with those big tires on there, she doesnt want to move. I just need more power (and gears, AGAIN!). Well I trust you guys' opinions, so if you could just let me know whats good and whats not I would really appreciate it!

    Thanks!!!!

    88' K5 Silverado 9" Lift 38" Swamper TSL's
     
  2. jwduke

    jwduke 1/2 ton status

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    Unless you are going to build, a mega horse motor, you are probably better off with a 2 bolt main block. They have some give in the bottom end & are a dime a dozen to buy. I don't think GM has put out a 4 bolt 350 (For light duty trucks), for quite a few years. A four bolt main block is kinda like a steel crank, it is over kill for a daily driver/occasional offroader.

    1 ton '87 Chevy SWB in the making!
     
  3. 95 Silverado

    95 Silverado 1/2 ton status

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    you will get many different opinions on this subject. The four bolt main engines were used in truck engines and high performance applications from the factory. passenger cars had two bolt main blocks. the four bolt blocks provide a stronger, more durable bottom end. you will not get more power from a four bolt block. if you are building a moderate performance engine for street and four wheeling, a two bolt main block will hold up, if you can get a four bolt block for about the same money get it for the added strength, but don't feel that you have to have it to build a good engine. If your building something for race only, high rpm use then you need a four bolt block.

    '95 Chevy Silverado 1500
    5.7 V8-NV4500- 3.73 rears
    See My Toys: <a target="_blank" href=http://community.webshots.com/user/wdb172454>http://community.webshots.com/user/wdb172454</a>
     
  4. Thunder

    Thunder 3/4 ton status

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    I like those SDPC TBI 350s. 330 HP is good ammount of power out of a computer controled engine.
    I would put one in my K5 if I needed a engine
    A two bolt main shouldn't be much of a problem unless you are planning on towing a house.
    Or going on the bottle(NOs)
    2 bolts are plenty strong for everyday use.

    What are your plans for your K5?
    How hard are you going to use it?

    <a target="_blank" href=http://coloradok5.com/gallery/Thunders-Blaze> Blazer pics</a>

    <font color=blue>Nevada... Where the pavement ends and the west begins
     
  5. Sparky87k5

    Sparky87k5 1/2 ton status

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    GM's 350HO 300 &amp; 330hp motors are both 4 bolt mains as are all the higher hp versions. In reality, not really a need if RPM's are kept below 5000. Not many cases where RPM's above that are really needed in a K5 though.

    87 K5, 427BBC,D60 & 14BFF, NV4500, NP208, TSM disc's,
     
  6. holyjohnson

    holyjohnson Registered Member

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    2 bolt mains are good enough for anything under about 400 horse and under 5500 rpm
    so unless your going to add nitrous oxide and rev it out to 7000 all day it dont make that much of a difference
    trucks and performance cars came with 4 bolts originally because they didnt have the bearings we have today or crossdrilling or the polished journals we now have.
    and were intended to be worked pretty hard.
    goodluck

    "well,are you gonna pull them pistols,or whistle dixie!?"
     
  7. 91K5

    91K5 1/2 ton status

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    A 2 bolt block will hold up to more than most people think. 4 bolts are actually better suited for use in front of a manual transmission, or a HIGH HP/winding engine. There are actually some blocks that are stronger in the 2 bolt than the 4 bolt version. The extra hole on each side can make for a weaker main cap. I think this was a issue with the 400 small block, but might be present in other motors. I run a 396 big block, 2 bolt cast crank with about 450 HP and wind it to over 6 grand just fine, but the big block is beffier too. Just my .02
     

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