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Old 06-20-2001, 05:27 PM   #1
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Member#: 1346
Join Date: Apr 2000
Exclamation Running Borla headers without a muffler not reccomended

I just had some 2.25" pipe bent for my exhaust, and since the muffler shop is incredibly busy I got the pipe done today despite being without my new Borla muffler.

All I can say is that it's loud, blaringly loud, and that it's not a good idea.

It's been a terribly hot, muggy day, and the new, bigger crush-bent pipe hasn't done anything for performance...if anything it's slower and louder. I guess I can attribute this to another 90 degree bend at the end to keep the exhaust from hitting the heat shield, but I'll avoid any comparisons until further 0-60 research is conducted.

Anyway, it's devastatingly, terribly, teeth-rattlingly loud. Straight pipe + Borla headers + H4 = bad idea. Trust me.
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Old 06-20-2001, 05:30 PM   #2
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when you go back for the muffler, remove all the heat shields.
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Old 06-20-2001, 05:30 PM   #3

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16 WRX (white)
04 FXT (red)


Any cats? Thats gotta be louder then my setup.

Ludespeed stg III, 2.5" DP, single high-flow cat, 3" straight back. Wakes up the sherrif in the next town. Planning on a resonator and muffler ASAP.
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Old 06-20-2001, 05:31 PM   #4
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I could have told you that,

You are now running a pretty much backpressureless exhuast system now..

Thats one of the mufflers job, to provide a certain amount exhuast backpressure that the engine needs to perform the best.

Get yerself a muuufflllllerrrr! hehe

Jay McDade
Auto Tech--Lincoln/Mercury/Jaguar
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Old 06-20-2001, 09:49 PM   #5
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Colin, are you sure about that? I mean, I told him I wanted some of the heat shield cut when I'm coming back, but remove the whole things? What difference will it make if I cut away the edges that I think are the source of the rattling?

Nick-it's gotta be louder. I set off two car alarms today and terrorized countless small mammals.

Jay-I thought that the trick was to have a constant velocity once the gases leave the engine. I'm pretty close-no hi-flow cat, since it'll take me out of STS, but other than that, 2.25" catback piping and headers with a 2.25" outlet to the cats. I think the cat piping is 1 7/8s? So it's not much of a chokepoint.

I need a muffler badly, though, you're right...this straight pipe stuff is for the guys whose mullets provide hearing protection. Aieesh.
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Old 06-20-2001, 10:58 PM   #6
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I had headers, MSD and intake on my old geo tracker. I tried straight pipe on it for one day, and then had them weld the flowmaster back on the next. A FM should sound interesting on this car... G
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Old 06-20-2001, 11:30 PM   #7
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no...no headers equals loud
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Old 06-20-2001, 11:36 PM   #8
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90' MX-5/11' DGM STi Sdn


yeah.. when we were installing my borla headers..

OF COURSE we started the car up without the Headers on at all..
and it IS insanely loud..

we also ran it headers.. with the cat disconnected.. also loud.
but not as loud.
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Old 06-21-2001, 12:21 AM   #9
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Smile brrrr

get a sound clip... or better yet a video clip. Start it up on a crowded street and get their reactions. Hi, I'm Jhonny Knoxville and this is NO MUFFLER.
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Old 06-21-2001, 04:37 AM   #10
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meebs: actually i did take sound clips of it. check my junk files on my aol account here- http://members.aol.com/specopsrb6

its somewehre up there. not the best quality but you get the idea of how loud it is. i remember when i did the no header sound all the dogs in the neighborhood were going crazy.
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Old 06-21-2001, 07:52 AM   #11
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Reset your ECU to help resolve some of the loss in power with the bigger pipes. I was driving around on a 2.25 midpipe and stock muffler for a long time then added a larger muffler. I lost a bit of low end until I reset the ECU.
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Old 06-21-2001, 09:44 AM   #12
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If you go turbo your back-pressureless exhaust will be great for that setup. NA cars work best with the right amount of backpressure in the exhaust. Turbo cars work best with an exhaust flow that is as free as possible.
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Old 06-21-2001, 11:46 AM   #13
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Blue or something

Default no no no no no no no!


Once again, the confusion of 'backpressure' with 'exhaust velocity'...

Shortening the exhaust (and increasing pipe diameter) both reduce exhaust velocity. Higher exhaust velocity will help 'suck' the air/fuel mix into the cylinders during the short moments of overlap when both the intake and exhaust valves ( I know there are four) are at full open. Even when the engine isnt in the middle of an exhaust stroke (and thus expelling gasses), the exhaust gasses are still traveling out the pipes because of thier own momentum. That is the action that most commonly is referred to erroneously as 'backpressure'

True backpressure is always bad, be the engine N/A or turbo. Thats just how hard the piston has to work to expell the gasses on the exhaust stroke. A turbo benefits the most from the lowest possible backpressure because there is plenty of positive force cramming air into the intake.

Consider the historical banana up the tailpipe. That's backpressure at its greatest, although the analogy is a little extreme.

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Old 06-22-2001, 08:03 AM   #14
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2000 Impreza 2.5 RS
Dirt and Bird Poop


How does increasing diameter INCREASE velocity??? Thats not right... It may increase flowrate, but it will not increase velocity.... Not unless the smaller diameter tubing is so restrictive that it actually causes that much back pressure...

Simple physics tells me that decreasing pipe diameter will increase velocity (and probably pressure, too).

Of course, I was wrong once before... it could happen again...
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