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Car Q: Advantages of True Duals?

Discussion in 'Off Topic [BG]' started by Stu L., May 19, 2005.


  1. Stu L.

    Stu L. Supporting Member

    Nov 27, 2001
    Corsicana, Texas
    What, if any gains are available if I break away from my 1 in 2 out exhaust and run true duals (down pipe->cat->muffler *2)? Any extra horsepower? I assume more noise, but thats not important enough to make me spend the $. Thanks in advance.
     
  2. Basschair

    Basschair .............. Staff Member Supporting Member

    Feb 5, 2004
    Stockton, Ca

    Hey, how could 10 million Hondas be wrong? :smug:

    What car, current HP, etc.?
     
  3. Generally, yes. But there a multitude of factors that i'm too stupid to include in my answer.

    Mike
     
  4. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    It depends on the vehicle. It allows for better flow, because an engine is basically a pump. But, the cooling effect of the exhaust will basically pull the gases along until they exit the pipe. But, if the pipes are too large, you will negate the effects of the added flow. It's interesting how the cooling effect will pull the other gases along. Also, if you want to take advantage of the higher flow, you can also put in a higher flow intake.
     
  5. Stu L.

    Stu L. Supporting Member

    Nov 27, 2001
    Corsicana, Texas
    :D

    '04 GMC Sierra, V6. As for current HP, no idea. It currently sports a custom built muffler back system, and a K&N filter. I do pull a trailer a few times a month, so HP is important. I do have enough HP for that already, I just want more :)
     
  6. Mike N

    Mike N Missing the old TB

    Jan 28, 2001
    New York
    Funny, I always thought that cool exhaust gases become lazy, and then need to be pushed from the exh pipes rather than making their own way out.

    This was why NASCAR and other racers wrapped their headers with insulating tape......to not only keep underhood temperatures down but to keep exh gases hot and thus moving in the pipe (and increasing the "scavenging" effect).
     
  7. Mike N

    Mike N Missing the old TB

    Jan 28, 2001
    New York
    You could probably pick up some more power (and economy) with true duals, but it may not be enough to justify the cost. I wouldn't expect 50 hp and 10 more mpg, but 10-20 hp and an extra 2-4 mpg is a real possibility.

    Remember too that your computer and oxygen sensors (along with your local DMV) may not like an aftermarket system, so make sure whatever you look at is CARB and 50 state certified.
     
  8. Stu L.

    Stu L. Supporting Member

    Nov 27, 2001
    Corsicana, Texas
    As much as 20 hp and up to 4 mpg, I would consider that a nice little gain. Short of buying expensive computer upgrades, this seems like a nice choice.

    As for the DMV, we're all good there. The only big no-no around here is an open element air filter. Those won't pass inspection. As long as you have a muffler looking device under the vehicle, and a cat looking device, your pretty much good to go.
     
  9. Stu L.

    Stu L. Supporting Member

    Nov 27, 2001
    Corsicana, Texas
    So with duals, would pipe diamater need to be decreased?
     
  10. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL

    The scavenging effect is due to controlled cooling. You gotta think that a Nascar does not usually go below 120 mph. This is a lot of moving air. The insulation is also for fire prevention. If oil was to hit a hot exhaust on a nascar, the results could be bad. But for a regular road use vehicle, the cooling is what makes the scavenging happen. Think of it like this... When a pulse of exhaust gasses exits the engine, it is hot and large, and it is being pushed out, but when it gets away from the engine, it starts to cool. This little packet of exhaust contracts when it cools, and creats a lower pressure cell, which the exhaust from the engine rushes to fill. This makes a pulling effect, which makes the exhaust stroke of the engine easier.
     
  11. Basschair

    Basschair .............. Staff Member Supporting Member

    Feb 5, 2004
    Stockton, Ca

    Good old Texas :D
     
  12. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    I think with a V6, you would not go above 2" pipe per side. Also, do you have headers, or regular manifolds?
     
  13. Another factor is How much "Back pressure" your engine likes. The Gm V8 in my 05 tahoe likes a moderate amount of back pressure so a true duel would be overkill in that situation. I haven't any experience with your 6er so??? try going on one of the GMC or Chevy forums and see if you can find some dyno results.

    In some of the engines I've tuned its really hit or miss untill you find the right synergy of products. Realisticly I wouldn't expect more than 5-10 HP gains on just swaping exausts (naturaly asperated engine) with out other engine managment, no matter what the manufactuers claim.
     
  14. Tash

    Tash

    Feb 13, 2005
    Bel Air Maryland
    This is a big one actually, though it hits stronger on the intake end than the exhasut end. Many cars will adapt the fuel/air mixture and spark plug timing to when the ECU sees coming in in terms of oxygen. They are programed to shoot for certain optimum combinations. If you add more O2 by increasing airflow the system will compensate to keep running close to what the manufacturer has determined is the "optimum" setup, which negates any advantage the add on got you.

    I saw this when I was tuning my old Z3: cat back, header and CAI got me no noticable inrease in power (didn't dyno the car but I was tracking regularly and got no faster). I got a new chip for the ECU suddenly had a much faster vehicle under me.
     
  15. Here's just what you need -
     

    Attached Files:

  16. Stu L.

    Stu L. Supporting Member

    Nov 27, 2001
    Corsicana, Texas
    Thanks, but I already had an Explorer ;)

    So, as for pipe size, the current aftermarket exhaust is same as stock. IF I decided to go dual, the new one would also be the same size (in other words, I have no intention of increasing size).

    Well, at least I have yet to see a negative :meh: or did I miss it...
     
  17. Mike N

    Mike N Missing the old TB

    Jan 28, 2001
    New York
    Sorry, I gotta disagree. Exhaust gases lose velocity as they cool, which reduces the scavenging effect.

    I remember the old drag racer trick of tuning the headers via collector length. You would take a wax crayon and draw a line on the collector. Next, take a trip down the 1320 and then look at the line on the collector. When you find the point that the wax stopped melting, you would cut the collector there. It was at this point the exhaust became to cool to aid in the scavenging effect.
     
  18. MJ5150

    MJ5150 Terrific Twister

    Apr 12, 2001
    Lacey, WA
    Yeah, I'm going to side with Mike on this one. When you start running 10.3's Trevorus, then maybe I'll agree with you. :D

    -Mike