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Thread: 2 1/2 vs 3 inch Exhaust

  1. #1
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    Question 2 1/2 vs 3 inch Exhaust

    What are the benefits of having 3" exhaust over the 2 1/2 inch exhaust to the rear?
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    An engine is like an air pump... more incoming air and more exhausted air is better.
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  4. #4
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    I know there was supposedly some benefit to having some back pressure with the smaller exhaust but see some people running with the larger 3" exhaust all the way back. I wondered if there was a hp benefit to the larger exhaust.
    Last edited by vkirkend; 10-15-2014 at 08:22 AM. Reason: sp
    2004 MM (Black) #112 of 3213 (SOLD)

    2022 Ford Ff-150 SuperCab Iconic Silver "Powerboost"
    3.35 L 4X4
    -AND-
    SLAYER1
    formerly owned by "Impala Slayer!! 2004 SB MM
    Kenne Belle 2.8 (Liquid Cooled), MMR "Boss 302" Block, L&M Engines rebuild Kooks Headers and cats, Accusump Pre-Oiler Dynamax VT mufflers, MBS 2 1/2" exhaust, 4.10's, 2800 stall, Argento 312 "Color" Powder coated wheels, Rears widened 1 1/2 "703
    702 RWHP/653 RWTQ @ 21 Lbs. Boost, M/M catch can, 3 pillar gauge (Boost, Fuel, air intake and coolant temp, custom console cover, S-55 treatment etc...

  5. #5
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    i thought the general rule was 1" total for every 100 horsepower,

    so only if your were planning on making 600+ RWHP would 3" exhaust be necessary

  6. #6
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    Quote Originally Posted by jwibbity View Post
    i thought the general rule was 1" total for every 100 horsepower,

    so only if your were planning on making 600+ RWHP would 3" exhaust be necessary

    +1^^^^^^^^^

  7. #7
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    Quote Originally Posted by jwibbity View Post
    i thought the general rule was 1" total for every 100 horsepower,

    so only if your were planning on making 600+ RWHP would 3" exhaust be necessary
    How do nine-inch tips figure into that ? I mostly see them on cars making about 125 hp, is that one inch of can per 15 hp ?
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  8. #8
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    Quote Originally Posted by jwibbity View Post
    i thought the general rule was 1" total for every 100 horsepower,

    so only if your were planning on making 600+ RWHP would 3" exhaust be necessary
    It's a good thing I went full 3"
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  9. #9
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    Quote Originally Posted by Comin' in Hot View Post
    It's a good thing I went full 3"
    Yepp ---the old rule of thumb was'' big block' pushing 600 hp can accommodate 3'' exhaust
    Roger that

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  11. #11
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    fopr most people's MM 2.5" is fine... but if you plan to run big power & Big boost / CFM then the #" exhaust is less restrictice. but if you havent had your headsw redone (port & polished) then the exhaust will not make a difference...

    If you cant get the xtra air flow thru the engine....

  12. #12
    Not much better for either one if you still running stock manifolds that's where its choking these engines .

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