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Minimum exhaust pipe diameter for BBC???

Discussion in 'The Garage' started by ak bandit, Sep 27, 2005.

  1. ak bandit

    ak bandit 1/2 ton status

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    I have 2-1/4" dual exhaust on my K5 now that was used for the 350. I'm swapping in a big block 396 and was wondering if I need to upgrade to larger diameter?
     
  2. RingMaster4x4

    RingMaster4x4 1/2 ton status Premium Member

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    I think that 2 1/4 -2 1/2 should be fine. The motor is mostly stock right? I put 3 inch on mine but if I had it to do over again I would go with 2 1/2. In your case if you pipes are good I would leave it alone. IMO
     
  3. zero cool

    zero cool 1/2 ton status

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    Pipes that small will be too restrictive at higher RPMs.

    If you hardly ever rev the engine over 3K, you'd be OK. When you get around to replacing the exaust (for whatever reason), I would take advantage of the opportunity to get bigger pipes. 2 1/2" minimum. More recommended.

    If it were my rig, I'd go with dual 3" at a minimum. But then again, I like the sound of a big block singing at 5K RPMs (or more) while I wag the tail all the way down the block. :D
     
  4. JEBSR

    JEBSR 1/2 ton status

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    Some of your factory big blocks came with single outlet 2.5 into 3 inch from the factory. With that in mind dual 2 1/4 will flow better and work fine. Will be a little too restrictive for a modified engine but fine if mostly stock. 2.5 would be nice to have, but unless you just have extra cash to spend on it I would leave it be for now
     
  5. muddybuddy

    muddybuddy 3/4 ton status

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    thought it was interesting that my k5 came stock with single 3" throughout. i went to advance auto and bought the factory pre-bent piping cuz mine was all rusted.

    i would do dual 3" when ya get a chance.
     
  6. ak bandit

    ak bandit 1/2 ton status

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    The 396 has mild build. It was dyno'd at around 375 ponies. It sounds like the 2-1/4" pipe may be boarderline of being too restrictive, if it's already isnt.
     
  7. destinbeachman

    destinbeachman 1/2 ton status

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    Just a bit small

    What you have is gonna be just a bit small unless it's bone stock and you don't plan any upgrades-even so it's gonna hurt you just a bit on power and gas.2 1/2's are right on for most BBC's but if you start playing with it you'll need 3's.Just figure out which one of these options suits you.Going a bit too big is way better than too small :D
     
  8. thatK30guy

    thatK30guy 1 ton status Premium Member

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    If you have headers, I would go 3" after the header to the muffler and then 2.5" after the muffler. :deal:
     
  9. destinbeachman

    destinbeachman 1/2 ton status

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    375 Hp

    3 inch would be perfect for that power range.Enjoy.By the way,can you round up the part number for that slick March Performance setup you have on there?Their catolog lists several and I can't straighten them out.I have to upgrade from the old misaligned crap I have now.Thanks-Allen
     
  10. ak bandit

    ak bandit 1/2 ton status

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    Thanks for the replies. I'll probably end up going with a 3"...I guess I can put those 2-1/4" delta Flow 50's on my '96 Z71 :D
    The March setup that I bought was #23020...I really like them. Quality and fitment are excellent. The belt lengths that they recommended were a 1/2" too long though. But that's not much of a complaint...
     
  11. Yukon Jack

    Yukon Jack 1/2 ton status

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    I went with 3" from the headers to the x-pipe. The X-pipe is 3" and necks down to 2 1/2" on the other side. Then I'm using 2 1/2" to the mufflers and on back to the hitch. Seems to work well with my bb. I went 3" because of the bends near the t/c. I figured if I had used 2 1/2", the bends would have been pretty restrictive.
     
  12. bigblockman

    bigblockman Newbie

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    bbc exhaust

    i had my exhaust done at a local shop. i have a 600 hp 454 and they told me for the best optimum backpressure that a bbc wants 2.5" is best 3" flows too much and doesnt give enough backpressure the motor needs it to equal out
     

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