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Exhaust 1:1 out vs 1:2 out

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by ftn96, Apr 27, 2002.

  1. ftn96

    ftn96 1/2 ton status

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    Right now I have headers with single out. What sorta difference sound or performance wise would I see (if any) from going to single into dual out?
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    To get any more flow you'd have to go with dual cats, or one larger cat. Either way right now your Cat is probably the restriction and anything behind it won't have too much effect on performance. It might sound a little nicer with dual tailpipes though.

    Rene
     
  3. ftn96

    ftn96 1/2 ton status

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    Like how much better sounding, maybe? Deeper, more quiet or what? Come on $hitter, I need details.../forums/images/icons/wink.gif
     
  4. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Probably a bit deeper and more rumbly. I had an 88 GMC pick-up that was 3" single into a single muffler with dual 2 1/2" tailpipes and it had an awesome exhaust tone. It sounded like true duals...

    Rene
     
  5. joker89blazer

    joker89blazer 1/2 ton status

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    I think it was four wheel and off road that done a test on this (may have been another mag). The 3" single pipe flowed same horse power as duals with cross over pipe. Duals with out cross over pipe did not do as good as with either one of the other two. I think that a cross over pipe are a large single pipe would give better bottom end torque for low speed use , such as rock crawling. On my truck I run duals with 2 1/4" pipe and dynomax mufflers and no cats ( no sniffer tests in florida..... yet) Sounds great when you step on stupid pedal but mellows out at cruising speed . Only problem is I ran pipes out back of blazer and truck will suck fumes inside when windows are down. I don't know why but those large 3-4" tips seem to give a good mellow tone, I tried truck with and without tips.
     
  6. wheelnut46

    wheelnut46 1/2 ton status

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    I dont know if this can be done, but I'll throw it out there anyway. What about the idea of a true dual system with the CAT being the crossover pipe. The cat needs to be there, for inspection purposes but it would be so much less restrictive there. The only problem with that idea is I dont know if CATs are directional. Like I said, I dont know if it's do-able - just an idea.
     
  7. Thunder

    Thunder 3/4 ton status

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    I dont think you will see any performance diference. Believe it or not, but a single 3" pipe flows almost as good a dual 2 1/4" system. The larger diameter pipe flows better than smaller pipe
     
  8. ftn96

    ftn96 1/2 ton status

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    But, will I notice a big difference from no muffler now to 50 series flowmaster with single factory exhaust routing, well except that is goes via the Thorley headers and an aftermarket CAT.
     
  9. wheelnut46

    wheelnut46 1/2 ton status

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    I ran dual aluminized 2-1/2 pipe on a 3/4 ton pickup I used to have and if I remember right, 2-1/4 is .064 inch wall thickness and the 2-1/2 is .078 inch wall thickness. That might not be exactly right (its been a few years) but it should be close. So 2-1/2 inch is larger and the wall thickness is greater so it should last longer.
     
  10. 84_Chevy_K10

    84_Chevy_K10 Banned

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    That wouldn't work. Exhaust takes the path of least resistance and most would bypass the cat completely.
     
  11. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    They do make a dual in/dual out cat if you wanted to go that route.
     
  12. wheelnut46

    wheelnut46 1/2 ton status

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    That is my point. You get credit for having the CAT connected but in reality it doesn’t really do much. There are no performance robbing characteristics. Also almost no environment-friendly characteristics. It up to the owner to decide what’s important to him. None of my cars/trucks require CATs so I cannot conduct this experimant myself. I only threw the idea out to see if it was feasible.
     
  13. Blue85

    Blue85 Troll Premium Member

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    a 2 1/4" pipe has a cross section of about 4 square inches. 3" pipe has a cross section of about 7 square inches. Therefore, a pair of 2 1/4" pipes has about 13% more area.

    However, that doesn't mean that the two smaller pipes flow with 13% less restriction. A different diameter pipe also effects the turbulence and general flow characteristics. It also depends on greatly on the length and the number and types of bends in the pipe. A single exhaust will almost always have a greater system length, since you need a crossover pipe somewhere and if you go to dual exhaust after the cat, that adds some lenth as well.

    A single 4" pipe (like on Cummins, etc.) is almost the same cross section as a pair of 3" pipes!
     
  14. four_by_ken

    four_by_ken 1/2 ton status

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    If your state requires a cat, running it as a cross over pipe will not pass you.

    Ken H.
     
  15. 84_Chevy_K10

    84_Chevy_K10 Banned

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    You'll lose the effect of the crossover if it's blocked with a cat--and it won't do anything to help clean the air. It'd be a total waste of money.
     

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