2.5" or 3" Exhaust...

Discussion in 'Technical' started by geron, Oct 27, 2016.

  1. geron

    geron National Petroleum Equipm

    Hi Gents,

    Just wondering...

    If a car is running on 18lb boost with 555's and Nistune, what would be an appropriate size exhaust?

    Would a 2.5" cut it or go 3" from Turbo back. When I say turbo back I mean from the OEM short dump pipes back, where the O2 Sensor is installed.

    I think that a 2.5" would be plenty and 3" massive over kill.
    Here is a video comparing 2.5 & 3" with an engine doing 600HP.

    https://www.youtube.com/watch?v=_PVXvHkr-Vs

    Logic tells me that a car running 18 or 16lb boost on standard internals with 555's (no head porting) won't even get close to 600HP which will make the 3" superfluous and a 2.5" mandrel bent will be plenty.

    Having said that, a 3" will allow for quicker turbo spool perhaps, not sure.

    What do you guys think?

    Peter
     
  2. Fists

    Fists Well-Known Member

    You could go either at with your set up, depends whether you value occupant comfort/neighbor relations above getting every single hp out of your car.

    Americans usually talk about horsepower at the crank (even when they say wheel hp, it's generally measured at the wheels and corrected to the crank), high boost stock turbo Zs seem to dyno in the 350-400hp bracket here in aus so you're probably not as far behind that dinosaur as you think.

    Edit: oh, and if you're going 3" you should really go bigger/better dumps too to actually get those few percent more power.
     
  3. geron

    geron National Petroleum Equipm

    I already have a 2.5" system (short dump pipe back) with 2.25" at the last bit at the rear with restrictive mufflers due to noise. The tuner suggested 3" but I believe it's overkill.

    Currently looking at these: http://www.dynomax.com/
    I will get into contact with them and see what they can do for a TTZ. Hopefully they will have 2.5" mufflers that fit and are reasonably priced.
    I love this idea for mufflers.
    Also, I like the UAS X pipe setup which looks like a large muffler with two pipes in and two out. It looks like it only comes in 2.5". I think this would also help reduce drone.



     
  4. rob260

    rob260 Administrator Staff Member

    No point fitting a 3" exhaust behind standard dump pipes.
     
  5. Martin Williams

    Martin Williams Well-Known Member

    I agree with Rob. Get some decent dump pipes. It will mean you will have to get your exhaust modified to fit. You are already spending decent money, this will give some more performance.
     
  6. ProckyZ89

    ProckyZ89 Senior Member

    I also agree with rob

    Proper dumps and a good 2.5 system will handle it perfectly :)
     
  7. geron

    geron National Petroleum Equipm

    Thank you Gents.

    So replace the short dump pipes with aftermarket 2.5" and stick with the 2.5" exhaust all the way:)

    It's not a big deal to modify the exhaust to fit the new dumps so that's great.

    I much appreciate the advice b/c trying to decide on this issue was a bit of a headache.


    Would something like the UAS 2.5" cross over centre muffler be of any benefit if running dual flow mufflers?
    Would it be necessary to fit one? Currently 'H' pipe installed.

    Current exhaust is 2.5" with hiflow cats and dual hotdogs/side.
    I can either ditch the hotdogs to fit the UAS style cross over centre muffler or just keep them and don't bother with the UAS type muffler.

    Or perhaps ditch the hotdogs altogether and just have the dual flow mufflers.

    Now Trying to figure out the next step in the exhaust design.

    Any suggestions?


    Peter
     
  8. kickerzx

    kickerzx Member

    Well.. Do this experiment with me. Try breathing or blowing through a straw. You know, softdrink kind of straw. Hard to do?
    Now try cutting the straw down to a centimeter or two. Now breathe/blow through it... Any difference?
     
  9. mtopxsecret6

    mtopxsecret6 Member

    You better be at home actually doing this experiment too.. haha:p:D
     
  10. East Coast Z

    East Coast Z Well-Known Member

    Try this experiment.
    Try breathing or blowing through a 12' piece of 2.5" exhaust pipe, then a 3" piece of exhaust pipe of the same length.
    Any difference?
     
  11. rob260

    rob260 Administrator Staff Member

    Ha I don't need to do the experiment to know what the result will be.

    Enough testing has been done to establish the benefit of fitting 3" dumps to standard turbos. I'm very sceptical of any benefit in fitting a 3" exhaust to standard dumps compared to a 2.5" exhaust but I'll happily stand corrected (I have no attachment to either theory) if someone has actually tried it.
     
  12. rob260

    rob260 Administrator Staff Member

    If you are going to the trouble of changing dump pipes get the specialtyz 3" expansion style pipes. Cheap split flange 2.5" as sold by Z1, czp, tuneagent, n*power etc actually choke the exhaust; that's an experiment I HAVE tried.
     
  13. kickerzx

    kickerzx Member

    I actually have done it previously. Now, did you guys?

    If i had lungs with the capasity of a 3litre twinturbo im sure i would notice a difference. You can test this if you find a straw with a bigger diameter and tape it to the short piece of smaller straw...

    Edit. I aint saying the guy needs to go with a 3" exhaust. 2.5" is probably more that enough for what the engine is capable of. Just saying that everything in regards to increasing the exhaust (even if the dumps remain stock) helps.
    To attack this from the other end. Is there no point in upgrading all your intakepipes (so called breather mods nowadays) if you dont upgrade your throttlebodies? I meen the TBs are still the same smaller diameter as before..
     
  14. Fists

    Fists Well-Known Member

    The comment you originally replied to was about going 3" after stock dumps not going 3" in general. A 2.5" system with good mufflers but stock dumps the dumps are going to be the main restriction, you'll see more gain going to good dumps than upsizing the section that already flows well.
     
  15. kickerzx

    kickerzx Member

    Absolutley
     
  16. SrAfciGeR

    SrAfciGeR Member

    2.5" dump pipes and 2.5" full exhaust with 2.5" high flowed cat's should be sufficient enough.

    If going up to 3" dump pipes then would be advisable to go with 3" pipes and 3" cat converters, after cat's restriction to 2.5" wouldn't be that noticeable in terms of power loss.

    And something that makes nice tune and has great flow like 2.5" Cherry Bomb VORTEX as a Mufflers of choice...
     
  17. geron

    geron National Petroleum Equipm

    Thank you guys for all the information.

    Also, those 2.5" Cherry Bomb VORTEX mufflers look pretty good.

    I like the idea of 3" dump pipes with 3" cats then 2.5" all the way.

    Also thinking of using a Cherry Bomb Vortex muffler 2in/2out configuration as a centre muffler after the cats to eliminate drone and then I could use the Cherry Bomb Vortex mufflers 1in / two out one on each side to pretty much wrap this up.

    The way I see it, this system will have excellent flow and it should also be relatively quiet.

    http://www.dansmufflershop.com/contpics/cherry.jpg
     
    Last edited: Nov 2, 2016
  18. SrAfciGeR

    SrAfciGeR Member

    I think that you should be fine without centre muffler as Vortex design is specially designed to eliminate the drone. 1in /2out on each side would be perfect in my opinion at least :)
     
  19. ZDUCTIV

    ZDUCTIV Active Member

    At that power level I'd go full 3".

    http://www.twinturbo.net/nissan/300zx/forums/general/view/2033426/3-inch-parts.html

    Crucial points.

    Stock turbo'd Z, before/after 3" exhaust.

    [​IMG]

    Just for fun, same car:
    Blue line with single intake, 2.5" exhaust.
    Green line with dual intake, 2.5" exhaust
    Red line, dual intake, 3" exhaust.

    [​IMG]

    Sport 700 car before/after dyno.

    [​IMG]

    If you're not going to change out the stock dumps, don't bother at all.
     
  20. Sketchy

    Sketchy Sick to the power of rad

    That's a big call, the stock dumps (especially the passenger side) are ordinary at best.

    What was the amount of restriction measured?
     

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