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Thread: exhaust theory: what flows better, dual 2.5" or single 3"?

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    exhaust theory: what flows better, dual 2.5" or single 3"?

    this is currently justtheory, but lets say i'm building a street driven 350-400 hp pickup. what would be a better flowing setup, dual 2.5" exhaust with an X pipe, or coming of both headers with 2.5" into a Y pipe and running a single 3" all the way back? Assume i'm going to be using the same line of Welded mufflers, exhaust exit would be the same... which would be a better setup?

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    Re: exhaust theory: what flows better, dual 2.5" or single 3"?

    They're both going to flow the same... if the duals have an H or X pipe welded in place. The Y pipe setup would be fine & save the weight of the duals but then again.. would it be as cool to say 'Yeah, I've got a true Y pipe exhaust'..?

    But flow'd be about the same.
    I know how things go together & I'm not putting my 'Tab A' in your 'Slot B', dude..

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    Re: exhaust theory: what flows better, dual 2.5" or single 3"?

    I like the idea of a big single system - it screams practicality.
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    Re: exhaust theory: what flows better, dual 2.5" or single 3"?

    I know somebody has some mathematical computations to verify the facts. But first impression would be the duals. I know from a practicality standpoint I'm going to run a single 3". Sleeper and weight also ease and cost factors all make me want to do this.

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    Re: exhaust theory: what flows better, dual 2.5" or single 3"?

    I like the sound of the single better. One of these years I'll try to get some audio from my truck again.
    2003 auto Long Bed 4.3L ZQ8 + 2/3, Caltracs, rear disk, Auburn LSD, SS mirrors, Snugtop, 16" Zyrgo fan + VSC, 255/50/R16 Falken ZE-512, 2114 with 48LB Racetronix injectors, marine TB, TorqFlo Trans cooler, 2 BAR MAP, Accel 60115 distributor, A1000 FPR, Corbeau Forza seats, Mach headers, 2.5" front mount intercooler, Innovative turbo, Purple 3,000 RPM torque converter, EFILive COS3 tune.

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    Re: exhaust theory: what flows better, dual 2.5" or single 3"?

    I know I posted up the formula for exhaust sizing but I can't find it.

    150-250hp can use a 2" dual OR 2.25" single
    250-350hp can use a 2.25" dual OR 2.5" single
    350-450hp can use a 2.5" dual OR 3" single
    450-550hp can use a 3" dual OR 4" single
    550-650hp can usa a 3.5" dual OR 4.5" single

    This is a rough estimate because it assumes there's no power adders. These sizes are more like 'street/strip'. If you plan on doing all out racing go the next sizing up. Power adders, like turbos or super chargers, should get the next 1/2 size up.

    This is my sizing & don't take this as gospil... it's just an estimate boys & girls. (so don't get pissed at me if you're not happy w/ it!)
    I know how things go together & I'm not putting my 'Tab A' in your 'Slot B', dude..

    Quote Originally Posted by D-Caf View Post
    If you don't like it, then take it up with management. Just remember, I'm part of management and I DON'T WANT TO HEAR IT!

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    Re: exhaust theory: what flows better, dual 2.5" or single 3"?

    Sounds reasonable to me - I doubt there's any gain to be had over a 2.5" system on a bolt-on 4.3 for sure.

    When I had the S/C on with the 2.5" single and ultraflow muffler the shop couldn't get the wideband sensor to stay in the tail pipe on the dyno. The exhaust was going so fast it was either making a loud howling noise across the sensor or just blowing it across the room at high RPMs. They were pretty convinced that it was too restrictive at that point!
    __________________________________________________ ______________________________________
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    The Bird: '95 Firebird Formula ram air, LT1/T56.






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    Re: exhaust theory: what flows better, dual 2.5" or single 3"?

    Haha. Sweet
    I know how things go together & I'm not putting my 'Tab A' in your 'Slot B', dude..

    Quote Originally Posted by D-Caf View Post
    If you don't like it, then take it up with management. Just remember, I'm part of management and I DON'T WANT TO HEAR IT!

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    Re: exhaust theory: what flows better, dual 2.5" or single 3"?

    That chart looks about like the ones I've seen before.



    Imho on a street truck that has the gas tank in the way a good single is the way to go. A true dual is only good on something turning high rpms and flow is the only thing that matters. On the street a good x or h pipe helps at lower rpms to keep the exhaust moveing and should always be used.

    I think exhaust should be heard and not seen. Two big chrome pipes sticking out of the butt of a nice truck ruins the look.
    D.J.

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    Re: exhaust theory: what flows better, dual 2.5" or single 3"?

    mine dumps under the car before the axle but i like true duals off to the side of the car like the blazers come with stock.

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