How much pipe (length) for a custom exhaust? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 04-03-2007, 01:18 AM   #1
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Default How much pipe (length) for a custom exhaust?

Looking to build my own - how much pipe did others who have buy, and how many bends?
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Old 04-03-2007, 02:37 AM   #2
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I cut a whole and made it exit through the drivers side. Had to buy very little piping and I got my bends done by a local pipe bending shop. I think I got 4 feet and it turned out to be way too much.
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Old 04-03-2007, 02:48 AM   #3
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I haven't done my own, I saw one guy who had built his own use 2 90*s, one at the muffler going back and the other coming out the muffler going out the back.
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Old 04-03-2007, 03:32 AM   #4
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I made my DP and full exhaust using 2 U-bends and 1 4' straight pipe along with a Summit Racing Turbo muffler. The U-bends were from JC Whitney so they had quite long legs.
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Old 04-03-2007, 11:20 AM   #5
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lets see... turbo back following the stock system looks like:

90° for the outlet (smaller diam + reducer)
90° for the bottom of the downpipe
15° for a kink at the tranny
6-8" of straight from there to the cat
18 inches of straight for the cat
6-8" of straight from there to the kink
another 15° for another kink half way back
6-8" of straight from the kink to the resonator
18 inches of straight for the resonator
a few more straight inches to the diff
about 45° and 8" for the kinks at the diff
90° to exit the diff space
180° U to turn around to go into the muffler
whatever you use for the muffler
and a 90° to exit the muffler
a shiny chrome tip the size of a grapefruit.

I think I used 3x 3" U bends, a 2-1/4 90° for the turbine outlet, a 2-1/4 to 3" reducer, a 3" 90° for the muffler outlet, a 3" cat, 3" "bullet race" resonator, 3" magnaflow muffler, and 3 feet of straight pipe (give or take). plus the tip. there's enough straight on the U bends to fill in the rest of the straight space but extra straight pipe is cheap and easier because it's not squashed from bending.
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Old 08-18-2007, 02:54 PM   #6
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well i just ordered a 3" catalytic converter, 3" dynomax bullet for a resonator, Summit Turbo muffler, and a mandrel u bend from summit. I will probably just take it to a shop and have them weld it up for me. My current exhaust is 2.5" with just a cat and a glasspack and gets a bit annoying sometimes so im hoping for a little quieter as well as betta flows and maybe better boost control as well. I aint trippin off the flows.

oh i forgot to mention that I am still running a stock size cat which has got to be killing the flow.

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Old 08-18-2007, 03:29 PM   #7
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I'll have some 3" SS pipe for sale - I bought 18' for my exhaust... you know I didn't want to end up not having enough. OVERKILL
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Old 08-18-2007, 04:09 PM   #8
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www.muscleexhaust.com has great prices on Magnaflow stuff which is usually very quiet.
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Old 08-18-2007, 04:15 PM   #9
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I like to lay a lot of pipe.
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Old 08-18-2007, 10:59 PM   #10
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^ me too.







oh wait, heres my 3" exhaust. never measured it, but maybe this will give u some reference.

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mated to the turbo tony dp. lol
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Old 08-18-2007, 11:53 PM   #11
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Quote:
Originally Posted by Wideopentuning View Post
www.muscleexhaust.com has great prices on Magnaflow stuff which is usually very quiet.
I'm running a Magnaflow exhaust on a full 2.5" turbo back exhaust, a 2.5" freeflow cat, and nothing else. On full throttle it actually sounds like stock... with pubes. At cruise it sounds no louder or quieter than a peashooter stock exhaust. At idle it just has a burly, lumpy sound.

Also, I bought a 5' section of straight, 3 or 4 90's, and I think a couple of 45's. All those gave me enough pipe and some leftover.
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Old 08-19-2007, 02:32 AM   #12
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Considering the car has been boosted and running for a few months now, the how much pipe for an exhaust is (for me) a mute point.....

However for interest sake, a mate of mine who does good steel work put this little system together for me.....

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It's sitting very low in this pic, and has (long) since been reworked to sit higher, and the join has been brought back to right before the 90 deg bend into the muffler.
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Old 08-19-2007, 04:03 AM   #13
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Hawt. I liek ur welds.
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Old 08-19-2007, 07:32 AM   #14
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Thanks for the pictures guys, i am sure they will help quite a bit.
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Old 08-20-2007, 03:35 AM   #15
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what turbo muffler from summit do you recommend?...does any body know if the turbo muffler sounds good?
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Old 08-20-2007, 03:42 AM   #16
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Another good question, IMHO; how much did everyone spend on said exhausts?

I'm debating whether to go custom or buy an Enthuza.
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Old 08-20-2007, 05:30 AM   #17
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You can usually do a nice stainless system that uses Magnaflow(I always use a cat, big *** reso and a muffler) stuff and v bands for around $400-$600.
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Old 08-20-2007, 09:27 AM   #18
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For my 3" exhausts:

Vibrant pieces: One 5' chunk of pipe, one metalcore cat, one J-bend.

Add Magnaflow muffler size to taste.
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Old 08-20-2007, 09:40 AM   #19
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J-bend = 180* U bend? Or is it different?

Did you have to bend the 5' length at all or just run it from the cat to half the J-bend, into muffler, and then use the rest of the J-bend to route from muffler to exit?
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Old 08-20-2007, 10:55 AM   #20
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those estimates sound about right.

though if you want to save some coin, you dont need stainless pipe beyond the dp. it's nice, but aluminized will last a long time.


I recommend the magnaflow universal stainless (polished or brushed) in 4x9" by as long as you can fit. I have the 5x11x22 and it's real nice. and long.
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