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Question: What Size Pipe Do I Use For Dual Exhaust?

Discussion in 'The Garage' started by Looksback, Feb 10, 2003.

  1. Looksback

    Looksback 1/2 ton status

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    I have a '86 K5, with a 305ci motor, and I am thinking of dual exhaust, but I do not know what size pipe to use, I know there has to be some back compression so I do not want to use to large of pipe. Any suggestions on what size pipe to use?

    Thanks for the help
    LooksBack
     
  2. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    2 1/4" is your best bet. It will also work well with a 350 if you decide to upgrade when the ol' 305 kicks the bucket.
     
  3. Hossbaby50

    Hossbaby50 3/4 ton status

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    2 1/4" is what I went with. It works well on my 350.
     
  4. 90K5

    90K5 1/2 ton status

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    what they said
     
  5. Storm Trooper

    Storm Trooper 1/2 ton status GMOTM Winner

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    I used 2-1/2" Aluminized pipe and dual inlet/outlet Stainless Flowmaster muffler on mine but I have the 350HO.
    If you want to keep it for a long time and might upgrade the motor (like it or not) I would use 2-1/2". 2-1/4" will also work fine with your motor. Motors do like to breath and a good muffler will create all the back pressure you need.
     
  6. mplogic

    mplogic 1/2 ton status

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    My mechanic recommended 2.5" with cats only (no mufflers) but we were planning on swapping in a SB400 so at the last minute we decided to go with 3". It came out way too loud. It's kinda cool, but I've got to get some mufflers on there now to make some back pressure (and stop annoying the neighbors). 2"-2.5" is probably a good range depending on your intake, carb, cam, etc.
     
  7. Chris Demartini

    Chris Demartini 1/2 ton status

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    <font color="blue">Back when I had dual exhaust I ran 2 1/2".
     
  8. Looksback

    Looksback 1/2 ton status

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    Thanks for the help, that is what I had though might work so I think I will use the 2-1/4" pipe. as for the motor it is in perfect running condition so I will be a long time before a new one is needed. If I were to gett a motor my choice would be the 366ci big block, but I dont know if I would ever gett it to fit under the hood.
     
  9. mudhog

    mudhog THEGAME Staff Member Super Moderator

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    i have duel 2.5in on my 350 /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif
     
  10. Suffergauge

    Suffergauge 1/2 ton status

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    I run 2 1/2 myself. You might be able to get away with 2 1/4 with the 305.
     
  11. 91k5NC

    91k5NC 1/2 ton status

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    i went with 2 and a half and seems to be fine with a 350.
     
  12. Beast388

    Beast388 1/2 ton status

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    I've got 2.5" from the headers to the 40 series Flowmasters, then 3" from the mufflers up over the axle and out the back. It is lets the healthy 388 breathe pretty well. It is a little noisy, but sounds good when I press the go pedal /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif /forums/images/graemlins/burb.gif
     
  13. fortcollinsram

    fortcollinsram 1/2 ton status

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    I have a true dual 2-1/4" system behind my 350...I will be using either true dual 2-1/2" or 3" behind my BBC, but I am ditching the cats too...

    Chris
     
  14. Z3PR

    Z3PR Banned

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    2.25 for duels will give you the propper back pressure.
     
  15. NITRO

    NITRO 1/2 ton status

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    what would u guys use for a 454?? im thinkin 3" true duals all the way out and behind the tires. right now i have 2 1/2" for my 350, but it crapped so in comes the 454....

    NITRO
     
  16. Lonnie

    Lonnie 1/2 ton status

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    2-1/2" duals are good for your 454. Dual 3" is not really necessary until you are near 450hp.
     

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