2 BOLT VS 4 BOLT MAIN POWER CAPACITY

Discussion in 'High Performance Modifications' started by nova75mike, Feb 19, 2018.

  1. nova75mike

    nova75mike Veteran Member

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    Mar 20, 2008
    Etters, PA
    I know I'm opening a can of worms here, but please chime in. I had planned on rebuilding the 350 in my 79 Z as the previous owner had it all screwed up. The block ended up being a 2 bolt main, and my spare thats been sitting in the corner is also a 2 bolt, which has me rethinking my 480-500 HP 383 that's been spinning in the back of my mind. It will spend 80% of its time as a general cruiser, but will see the strip on occasion. I've had 2 bolts converted to splayed 4 bolts on my race only motors in the past, but the street is kind of new territory for me. With all the other work the car and drive train needs, I really don't want to spend the extra $$ to splay the mains if I don't have to. The floor is now open guys.
     
  2. 70lt1z28

    70lt1z28 Veteran Member Gold Member

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    Beavercreek, Ohio, USA
    At that power level you would be OK if you used good ARP studs and nuts instead of bolts. If you pound on it constantly and expect it to live to 100k then go with 4 bolts with steel caps. Do the caps fit tight in the block now?
     
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  3. nova75mike

    nova75mike Veteran Member

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    Mar 20, 2008
    Etters, PA
    The caps do fit tight and square. very little bearing wear when I pulled it apart. LOTS of cylinder wear tho. some cheap piston that doesnt even have manufacturer markings on it, scuffed the cylinder walls and grooved them pretty badly. likely have to go to 40 over.
     
  4. muscl car

    muscl car Veteran Member Lifetime Gold Member

    With a 2 bolt block I've seen 750 - 800FWHP. before seeing reliability issues
     
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  5. nova75mike

    nova75mike Veteran Member

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    Mar 20, 2008
    Etters, PA
    back 20 years ago when I first started racing, I had a snotty little 355 that put out 458 at the crank. twisted that thing mercilessly for 5 seasons till a wrist pin ate into the cylinder wall. pulled the thing apart and the bearings looked almost brand new. that was a 2 bolt. I think my main concern is the extra weight and stroke of the 383 crank putting more stress on the caps. I'll studs the mains and cross my fingers and toes.
     
  6. 70lt1z28

    70lt1z28 Veteran Member Gold Member

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    Beavercreek, Ohio, USA
    If its a cast crank its much lighter than the factory forged anyway. They pretty much went to the 4 bolt mains to deal with the heavier forged crank, and higher RPM. If you have a cast crank go for it but might want to spare the bottle, if that is a thought.
     
  7. nova75mike

    nova75mike Veteran Member

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    Mar 20, 2008
    Etters, PA
    It's one of the "Scat 9000 cast steel" cranks with their 4340 rods and speed pro pistons. I know the pistons and rods are on the heavy side. max rpm will be 6000-6500, no bottle tho.
     
  8. Lowend

    Lowend Administrator. .a car, a man, a maraca. Staff Member Lifetime Gold Member

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    San Jose, CA, USA
    Stud the mains and you'll be fine in a street car.
    Every Corvette L98 was a 2 bolt main, and even with some pretty nutty power levels you really didn't see failures.

    The more time goes on, but more I wonder if the "4-bolt is better" thing is real until you get into really wild levels of output
     
  9. nova75mike

    nova75mike Veteran Member

    319
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    Mar 20, 2008
    Etters, PA
    Its something that I heard so much when I was getting into cars, I just believed it without any real experiences of my own. I've shattered pistons, broken rods, cracked cranks, even cracked cylinder heads, but I've never broken a main cap on anything I've ever had. The poor 327 I had in my '75 saw 7k on a regular basis, sometimes more when I missed a shift (rev limiter was something only NASA engineers had back in those days), never had an issue with a main cap. on the other hand, they were all shorter stroke motors. when I went to the larger CI, I always converted to splayed cap 4 bolts.
     
  10. 70lt1z28

    70lt1z28 Veteran Member Gold Member

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    Probably wouldn't crack a cap, but they will start to walk around and then the bearings will fail. That's why I asked if they were tight in the block. If they are lose, then they have been walking and its best then to get steel caps and go to 4 bolt, line bore etc to tighten them back up. I've seen folks peen them to tighten them up but I don't trust that. You never know if they are centered perfectly before you peen and then when you peen one side it moves it one way and then peen the other side it moves it the other way.
     

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