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Thread: Getting a cat-back pipe size should I get?

  1. #1
    Join Date
    Dec 2008
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    Adelaide
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    Default Getting a cat-back pipe size should I get?

    Well I booked in today to get a cat-back installed next week.

    The exhaust shop did a cat-back system on a MPS6 a month or so ago and they said the last MPS6 had a 2 inch installed with straight through mufflers....

    The owner at the workshop said it sounded good, a friend of mine knows the owner of the MPS and he said he's really happy with the results and it feels like a better different car to drive.

    I'm not looking for advice to get a DP or not but I might look at one in the future....

    The last MPS 6 the workshop did they split the exhaust before the rear diff and the two pipes go either side of the diff (I had not seen this done before)
    then bend slightly through to the mufflers.

    2 / 2.25 inch sounds small..... I said I wanted minimal/no drone if possible.

    I'm looking for advice from people that have installed a cat-back and what they got pro's and con's

    I was thinking of two options...

    Option A- 2.5inch Cat-Back Y split before the diff, 2.5inch through to the straight through mufflers, flanged 3 inch tips

    or

    Option B- 3inch Cat to Y split before the diff,2.5inch through to the straight through mufflers, flanged 3 inch tips

    any option C's???

  2. #2
    Join Date
    Aug 2009
    Location
    Brisbane Southside
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    293

    Default

    2XS did a great job on my exhaust and I'm pretty sure it's a 3inch until the split after the muffler, then a 2 1/4 to the mufflers (left them stock).

    You can have a look at http://www.ozmpsclub.com/forum/intak...html#post55693

    I don't get any drone and it's as quite as a stock one until I rev it out. This may be related to the stock mufflers perhaps.

    I also just checked what is available on MPSGarage and both exhausts available are 3inch (not sure about after the split), and the downpipes are 3inch so I would be guessing that 3inch seems more common.

    Good luck with it mate.
    Red '05 6MPS.

  3. #3

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    The CP_e 3" SS catback (with inbuilt resonators and straight through mufflers) is well made but drones badly. Rattled my teeth and gave me a sore head. Some folks might like it but it was too much for me and my neighbours. One exhaust shop that looked at the setup as I was trying to decide how to quieten it down a bit reckoned that 3" was unecessarily large for the car, especially at the back end, where a 3" main pipe and reduced to 2.5 or 2.75" at the mufflers would be fine.

    I went back to my CP_e Downpipe and stock exhaust for now. I'll revisit it one day if someone can convince me that it will reasonably increase power over my setup, or if I want to smooth out the run at the Y junction.
    CP_e Standback & PNP; CP_e 3" SS Downpipe; Corksport FMIC with Top-mount K&N filter & OEM Ram CAI; Turbosmart BOV; Dashhawk; Prosport Boost Guage; JBR solid shift bushes; DBA 4000 Wiper-Slot front rotors; Hawk Ferro-Carbon HPS Street front brake pads (@ 69,000km); Sumitomo HTRZIII's in 225/45 x 18

  4. #4

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    Mine is 3" the entire way but I don't actually have a y piece splitting to two mufflers. Exhaust only comes out one side of my car :P As long as I don't blow smoke shouldn't be a problem!

  5. #5
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    Default

    I'm thinking 2.75 or 2.5 to the Y then 2.5 from there in to straight through mufflers.... 2.75 or 2.5? aaaggghhhhhh this is driving me crazy lol

    What is the size of the stock system?

  6. #6
    Join Date
    Aug 2009
    Location
    hunter valley
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    I dont own a 6 mps...but i would look at what i plan to do in the future modds department? if ur going down the larger turbo,dp etc path i think a 3'. if your only doing a couple of small modds i would go the 2.5'. I have a full 3' turbo back and it not to bad in my 3, i can hear road noise and intake over the exhaust no drone when off the throttle cruising. I have 2 mufflers 1 small round lukey and 1 offset lukey both are straight through.. no resnators in the system
    Many want Power not many hold it long.........

  7. #7
    Join Date
    Oct 2009
    Location
    Perth, WA
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    Default

    Option B sounds the works mate my 3" system below, complete with two resonators. Only drones a little on cold start but once the motor is warm, very little drone, sounds good and holds the same note to redline, some images FYI












    With great power comes great fuel consumption...
    M P S
    - 6 - RR | Cobb AP | CAI | TIP | ATP GTX28R | 3.25" TMIC | SS DP | REM | 3" Zorst | SSP Anchors & Countershift | DBA Rotors | K/Springs | Upper & Lower Bracing | Alpine Type S 12" sub MRP-M500 Amp
    | Grille | STi Lip | Shark Fin | 6000K HID | Fog Light Tint | Twin DEFI gauges | Custom Decals & Badges | LED lighting | CF Mirrors & Pillars | Black rims Red callipers

  8. #8

    Default

    Your pipe exits look good too ROG - and I didn't hear much noise when I was behind you when you were pulling out to pass.
    Last edited by Doug_MPS6; 04-08-2010 at 12:41 PM.

  9. #9
    Join Date
    Oct 2009
    Location
    Perth, WA
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    Quote Originally Posted by Doug_MPS6 View Post
    Your pipe exists look good too ROG - and I didn't hear much noise when I was behind you when you were pulling out to pass.
    Thanks Doug! You can definitely hear it when driving but as far as being 'loud' or having 'drone' its a great system. I would say my intake makes just as much noise if not more than the exhaust. In fact, I cannot hear my car even with the window up and a typical WRX pulls up next to me. Police don't often concern themselves with me as much as others 1) cause its a Mazda and 2) there is not a milo tin welded on the back. I used to have a Nissan Pulsar with a 3" Cannon on the back, I know all to well what drone is! I must say, very happy with the final product on my car. Two resonators wasn't my idea, rather I left it in Zacks hands and this is what he came up with.

    With great power comes great fuel consumption...
    M P S
    - 6 - RR | Cobb AP | CAI | TIP | ATP GTX28R | 3.25" TMIC | SS DP | REM | 3" Zorst | SSP Anchors & Countershift | DBA Rotors | K/Springs | Upper & Lower Bracing | Alpine Type S 12" sub MRP-M500 Amp
    | Grille | STi Lip | Shark Fin | 6000K HID | Fog Light Tint | Twin DEFI gauges | Custom Decals & Badges | LED lighting | CF Mirrors & Pillars | Black rims Red callipers

  10. #10

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    Sorry ROG, I meant "pipe exits" - a slip of the keys - now edited - same sentiment though.

  11. #11
    Join Date
    Jun 2009
    Age
    59
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    8,042

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    I went with a 2 1/2 inch on the MPS3 to keep the noise factor down and fuel economy and unless you have big turbo's a 3 inch can affect power and fuel economy which a friend from a mazda dealership learnt on a stock MPS3...


    P.S Maybe different on a MPS6 who knows..

  12. #12
    Join Date
    Dec 2008
    Location
    Adelaide
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    Ok I've decided I'm going to go 2 1/2 inch cat back, Y split before the rear diff (pipes go each side of diff) through straight mufflers to 3inch tips

    I will post pics and review of the setup after I do it in a weeks time

    Thanks for all your advice and pics!!!

  13. #13
    Join Date
    Oct 2009
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    Perth, WA
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    3 inch tips? Will that fit? Will be good to see pics of the install. Glad to help

  14. #14

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    3" tips do fit but you have to get them right so as not to rattle against the steel chassis just behind the SS oval shrouds. Even the install notes refer to a possible need to tweak the metalwork to gain clearance. See attached photo of my CP_e 3" SS tail-pipe setup before I removed it again. I'd stay with a maximum of 2.75" now. It's heaps of freedom for gas flow, given that there are two of them - it's easy to work out the relative volume relationships between 1 x 3" as opposed to 2 x 2.75" cylinders.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by Doug_MPS6; 04-08-2010 at 04:47 PM.
    CP_e Standback & PNP; CP_e 3" SS Downpipe; Corksport FMIC with Top-mount K&N filter & OEM Ram CAI; Turbosmart BOV; Dashhawk; Prosport Boost Guage; JBR solid shift bushes; DBA 4000 Wiper-Slot front rotors; Hawk Ferro-Carbon HPS Street front brake pads (@ 69,000km); Sumitomo HTRZIII's in 225/45 x 18

  15. #15

    Default

    3" out the tail is too big.. it will just drone like mad..

    by the time the exhaust is at the back of the exhaust it has cooled down.. and shrunk..kind of..lol

    2.5 out the tail is just fine

  16. #16

    Default

    Agreed. I think 2.5 - 2.75 is plenty.
    My CP_e drone came from the big pipe under the floor and the resonator which.........well..........resonated! But straight through mufflers contributed certainly. Look good though!

  17. #17
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    Oct 2009
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    Perth, WA
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    Can't remember the exact dimension on my tail pipe exits but it would be some where around 2.5". Zack didn't know how far I wanted the pipework to stick out the chrome shroud (tip) so he just went ahead and this was the result. To me, that's a close enough fit. Least it won't rattle and vibrate due to a larger clearance between pipework and the side wall of the chrome tip. Two resonators makes for minimal drone anyway, so if you go with 2x res, get any size tip and should sound ok?


    With great power comes great fuel consumption...
    M P S
    - 6 - RR | Cobb AP | CAI | TIP | ATP GTX28R | 3.25" TMIC | SS DP | REM | 3" Zorst | SSP Anchors & Countershift | DBA Rotors | K/Springs | Upper & Lower Bracing | Alpine Type S 12" sub MRP-M500 Amp
    | Grille | STi Lip | Shark Fin | 6000K HID | Fog Light Tint | Twin DEFI gauges | Custom Decals & Badges | LED lighting | CF Mirrors & Pillars | Black rims Red callipers

  18. #18

    Default

    Hi ROG, Yep yours look fine. Pretty subdued, you have to look hard to realize they are different from stock but more purposeful.
    I PM'd Carey today re my search for aftermarket tips, In the shops they are all too long an need to be cut down. If they stick out too far or accentuate the existing disparity between trim and pipe they look silly. It's hard to get it right. Cannons look silly and do just that.
    I need to re-measure my pipes again (I forget the existing diameter), then I'll look for a set that fit that dia. and step up to 2.5 or 2.75" but they will all need to be shortened, and possibly taper-cut to avoid the "cannon" look. The alternative is to get a custom shop to make a set up in SS, or in mild and get them chromed.
    CP_e Standback & PNP; CP_e 3" SS Downpipe; Corksport FMIC with Top-mount K&N filter & OEM Ram CAI; Turbosmart BOV; Dashhawk; Prosport Boost Guage; JBR solid shift bushes; DBA 4000 Wiper-Slot front rotors; Hawk Ferro-Carbon HPS Street front brake pads (@ 69,000km); Sumitomo HTRZIII's in 225/45 x 18

  19. #19
    Join Date
    Oct 2009
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    Perth, WA
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    Cheers Doug, I think it looks pretty much stock. In fact I think the whole exhaust looks pretty stock. I guess the only give away is a Stainless DP and mild steel cat back.

    Since we're on the topic of pipework outlets and exhaust tips, another option for the readers here is imaged below for your information and viewing

    Click image for larger version. 

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    With great power comes great fuel consumption...
    M P S
    - 6 - RR | Cobb AP | CAI | TIP | ATP GTX28R | 3.25" TMIC | SS DP | REM | 3" Zorst | SSP Anchors & Countershift | DBA Rotors | K/Springs | Upper & Lower Bracing | Alpine Type S 12" sub MRP-M500 Amp
    | Grille | STi Lip | Shark Fin | 6000K HID | Fog Light Tint | Twin DEFI gauges | Custom Decals & Badges | LED lighting | CF Mirrors & Pillars | Black rims Red callipers

  20. #20

    Default

    Quote Originally Posted by rogwick View Post
    Cheers Doug, I think it looks pretty much stock. In fact I think the whole exhaust looks pretty stock. I guess the only give away is a Stainless DP and mild steel cat back.

    Since we're on the topic of pipework outlets and exhaust tips, another option for the readers here is imaged below for your information and viewing

    Click image for larger version. 

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Views:	175 
Size:	94.2 KB 
ID:	4979
    A word of caution with the configuration in that photo: With the SS inserts removed there a risk of melting the plastic surrounds. A lot of guys have found this out the hard way and it's why SU sell them as a replacement part, but they are around USD$275 each side from memory.

    BTW Doc's comment is spot on. When the exhaust gases leave the engine they are travelling at supersonic speed at very high temperature. By the time the gasses reach the tail pipe they have slowed cooled and contracted significantly. The pipe diamater can and should decrease toward the rear of the car, even for turbo cars. But this is considered unconventional because accepted wisdom on exhasut design principles usually comes from guys who are not trained in fluid dynamics.

    Gone to Volvo


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