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Old 10-04-2009, 07:10 PM   #1
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Default Exhaust vs performance

A while back i got this exhaust, before going turbo. At the time, i didnt notice much of a performance boost, because i was still N/A.

Got a deal on an exhaust! - MX-5 Miata Forum

I added the turbo which made the sound a lot more manageable but it was still a little too attention-getting. I had a few minutes today so I swapped back the original exhaust (but kept the new magnaflow cat i installed), just to see how it sounded.

It's WAY quieter, actually too quiet.. It's kind of annoying actually, you hear practically no exhaust sound, it's all intake. More importantly, the car feels A LOT slower.. Im pretty sure it's not just in my head. The power comes on later and isn't nearly as much of a rush.

So my question is this -- since my 'loud' exhaust only a 2.25", and the power gains were significant, could I expect even larger gains by going to a 2.5" or 3" exhaust?

Even w/the louder exhaust i feel that i'm low on power til around 4k, so, i'm hoping that maybe a big fat exhaust will heelp!

Also on a side note, does a quieter / lower flowing exhaust also quiet the intake?? My bypass valve and intake "sucking" sound also seem diminished w/the stock exhaust.

-Tomaj
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Old 10-04-2009, 07:34 PM   #2
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3" straight through or bust.
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Old 10-04-2009, 08:12 PM   #3
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remember all your exhaust is now going thru a HUGE restriction. (the turbo) so the better flow you can make after it, the more power, the quicker spool etc.. also, yes, when you put your factory exhaust back on, it allowed much less exhaust out, which also hampered the amount of air coming in. (so less intake noise) biggest ex. dia. you can afford or fit is best. if you still wanna keep the noise down, get a large bodied muffler (maybe one of those oval ones) BUT, make sure it's a straight thru design. you should be able to look right thru it. also when you look in there, make sure it doesn't have little louvers that stick up to catch the air like a "glass pack'" usually has. even though it's straight thru, those little louvers make a huge impact on performance. it should be smooth inside with perforated holes.
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Old 10-04-2009, 09:35 PM   #4
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the difference between these two dynos was a new 3" exhaust from a 2.25" one and some mild headwork:

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Old 10-04-2009, 09:38 PM   #5
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ok got it.. Any suggestions for mildest sounding 3" exhaust? I saw the thread about the custom built exhaust w/the "biggest magnaflow you can fit" but now i can't find it..
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Old 10-04-2009, 09:43 PM   #6
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scott -- looks like there's a break-even point at 5250 rpms? I'm guessing the light colored lines are the 3" exhaust becuase you get so much more power down low right? (That would be what i want!)
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Old 10-04-2009, 10:12 PM   #7
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Brain, do you have any dyno results from 2.5 to 3.0?
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Old 10-04-2009, 10:15 PM   #8
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The red lines are with the 3" and the blue are with the 2.25". The light color lines are torque and the dark line is HP. They cross at 5250 because HP is calculated from torque and 5250 shows up in the equation.
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Old 10-04-2009, 10:27 PM   #9
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Wow i feel like an idiot for misreading that.. Please excuse me, i have a cold
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Old 10-04-2009, 11:26 PM   #10
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Quote:
Originally Posted by ctxspy View Post
ok got it.. Any suggestions for mildest sounding 3" exhaust? I saw the thread about the custom built exhaust w/the "biggest magnaflow you can fit" but now i can't find it..
The FM 3" system has a very nice sound, but is actually quieter than their 2.5" system. No drone when cruising and not cop-bait when in boost. Highly recommended.
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Old 10-04-2009, 11:50 PM   #11
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Ouch, it looks like right around $1k for the full 3" package, or a little over $700 if u don't get the 3" DP.

Would it make any sense at all to maybe do it step by step? Is it possble to weld on a 3" pipe to my cat to replace one on there, and just replace from the cat back for now, then when i have more $$ to spend, i can get the rest done?
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Old 10-05-2009, 01:00 AM   #12
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or you could get an aluminzed steel 3'' mandrel cut and weld system with a big straight thru muffler for half that much. or yes, you could get it all in steps. any muffler shop worth a **** should be able to do that for you.
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Old 10-05-2009, 08:32 AM   #13
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Quote:
Originally Posted by ctxspy View Post
scott -- looks like there's a break-even point at 5250 rpms? I'm guessing the light colored lines are the 3" exhaust becuase you get so much more power down low right? (That would be what i want!)
Lol, break even? Red is 3" exhaust with test pipe, blue is 2.25" borla duals with gutted 2.5" cat.

You want the biggest muffler you can fit up there otherwise it can be loud.
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Old 10-05-2009, 10:44 AM   #14
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Lol, break even?
yeah i totally misread your graph i was somehow thinking that the "light" colors were one set and the "dark" were the other.
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Old 10-05-2009, 11:35 AM   #15
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The enthuza I bought came with a 5x8x14" muffler. When I wrecked and had to repair it, I purchased a 5x8x18 to replace it. I decided it would be too much work to refabricate ****, and decided to get the same thing. I was dumb and bought a 4x9x14" muffler. enough though it's wider, the lack of the depth really hurt the sound dampening qualities and it's much louder than before. I added a resonator to it. It's liveable but its still a touch loud, but you're not going to get pulled over if you're driving around town. I'm hoping once I fit the cat in place it'll make it a little more civil.

Y8s is rocking a 5x8x21" muffler and it's by far one of the best exhausts I've heard. It has a perfect little grumble at idle, very liveable cruising dB, and has a great pitch at WOT.
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Old 10-05-2009, 11:42 AM   #16
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Quote:
Originally Posted by Braineack View Post
The enthuza I bought came with a 5x8x14" muffler. When I wrecked and had to repair it, I purchased a 5x8x18 to replace it. I decided it would be too much work to refabricate ****, and decided to get the same thing. I was dumb and bought a 4x9x14" muffler. enough though it's wider, the lack of the depth really hurt the sound dampening qualities and it's much louder than before. I added a resonator to it. It's liveable but its still a touch loud, but you're not going to get pulled over if you're driving around town. I'm hoping once I fit the cat in place it'll make it a little more civil.

Y8s is rocking a 5x8x21" muffler and it's by far one of the best exhausts I've heard. It has a perfect little grumble at idle, very liveable cruising dB, and has a great pitch at WOT.
5x11x22

it's a BIG MO FO
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Old 10-19-2009, 12:59 AM   #17
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Open dp ftw...

no seriously though I have the fm full 3" it has a great sound to it but it is kind of bitch to bolt up/line up talk a friend into doing it while u pretend to work on something else
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Old 10-19-2009, 11:38 AM   #18
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3" Aluminized, no cat and a 3" Magnaflow resonator in place of a typical muffler.



Not a cop magnet, nice warm sound when crusing and makes children cry at WOT.
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Old 10-19-2009, 10:44 PM   #19
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As I have concluded as well, straight back 3" with a 6" Magnaflow can won't be all that loud. Much quieter than most of the camaro/mustang crowd that have aftermarket exhaust. If you want uber quiet, just get one of the big Magnaflow oval mufflers.

Michael
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