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Old 08-23-2006, 05:15 PM   #1
qm8309
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Exhaust mod alone decreases low end torque?

I got a Borla cat-back installed after my factory exhaust went bad. It sure sounded sweet, but instead of feeling any slight "power gains" as advertised, I'm feeling some slight torque loss in the lower range. Like 2nd gear pull from 25mph feels weaker than before. Is this normal for an aftermarket exhaust without any other engine mod? Consider the borla is 20 pound lighter than the OE and supposely has better flow, I find it hard to believe that it could decrease the performance if not improving it.

Does getting an aftermarket exhaust mean I should definitely get other things like CAI and software? I never really wanted to engine mod my car though.
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Old 08-23-2006, 05:22 PM   #2
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I know at least on motorcycles such as the Suzuki Gixxers theres a flapper valve in the exhaust the allows for more backpressure at low end, I assume its to maximize the torque at all rpms. From that, perhaps the decreased backpressure from the higher flow exhaust without higher flow intake would reduce low end torque
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Old 08-23-2006, 05:25 PM   #3
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Quote:
Originally Posted by PreppyR6 View Post
I know at least on motorcycles such as the Suzuki Gixxers theres a flapper valve in the exhaust the allows for more backpressure at low end, I assume its to maximize the torque at all rpms. From that, perhaps the decreased backpressure from the higher flow exhaust without higher flow intake would reduce low end torque
What he said
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Old 08-23-2006, 05:26 PM   #4
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Yeah there's a flapper valve on the factory exhaust controlled by a little vaccum pipe. I simply sticked a nail into it and tied it like others recommended.

Will getting a CAI really improve the situation?
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Old 08-23-2006, 05:48 PM   #5
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ohhh man...i was thinking abt getting one in the near future...borla actually!!! hmmmm
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Old 08-23-2006, 05:52 PM   #6
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yes CAI should help
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Old 08-23-2006, 05:54 PM   #7
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u will gain high end hp and lose low end torque, cai will help a little but not like b4!

after some time u just get used to ot lol!
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Old 08-23-2006, 06:00 PM   #8
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Originally Posted by sanyomats View Post
ohhh man...i was thinking abt getting one in the near future...borla actually!!! hmmmm
I don't really think it's Borla's fault. Even the mech at the muffer shop said good things about the exhaust. It probably applies to virtually all aftermarket systems without supporting mods.

I will be looking into a CAI and software. But imo they are just too expensive for their little gains.
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Old 08-23-2006, 10:29 PM   #9
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if anything cai is a much better value for what you get then exhuast
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Old 08-27-2006, 04:05 PM   #10
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I thought aftermarket intake ALSO causes the lost on low end torque? From what Ive learned is that the aftermarket intake give gains on the mid and high end torque. That's what I feel too w/ my car.
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Old 08-27-2006, 04:17 PM   #11
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Originally Posted by qm8309 View Post
Yeah there's a flapper valve on the factory exhaust controlled by a little vaccum pipe. I simply sticked a nail into it and tied it like others recommended.

Will getting a CAI really improve the situation?
IIRC, the flap on the 330s is only used to decrease noise. It's absent on other models.
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Old 08-27-2006, 04:23 PM   #12
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What about exhaust + CAI + software then??? Is it still gonna cause low end torque loss???
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Old 08-27-2006, 05:22 PM   #13
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Originally Posted by qm8309 View Post
What about exhaust + CAI + software then??? Is it still gonna cause low end torque loss???
Get a rolling road mapping and you'll see an increase through the entire range.

If you change your exhaust + intake, your engine will not be running optimally. You *need* a remap for optimal performance.
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Old 08-27-2006, 07:14 PM   #14
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not enough back pressure...isnt it that only turbo/super charged really need that open ended exhausts?
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Old 08-27-2006, 07:21 PM   #15
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Quote:
Originally Posted by kerisabe View Post
I thought aftermarket intake ALSO causes the lost on low end torque? From what Ive learned is that the aftermarket intake give gains on the mid and high end torque. That's what I feel too w/ my car.
any intake that is exposed to the engine bay or runs from the bumper area will lead to the loss of low end torque. the main culprit is that the air comming in is not pressurized. Which is why the oem airbox is one of the best airbox designs ever. just dropping a new sports filter in will yield gains. but if you want something with power at no compromise, look into the dinan airbox as all the air is sealed as it improved over the stock airbox with a bigger lid/heat shield
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Old 08-27-2006, 10:03 PM   #16
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any intake that is exposed to the engine bay or runs from the bumper area will lead to the loss of low end torque. the main culprit is that the air comming in is not pressurized. Which is why the oem airbox is one of the best airbox designs ever. just dropping a new sports filter in will yield gains. but if you want something with power at no compromise, look into the dinan airbox as all the air is sealed as it improved over the stock airbox with a bigger lid/heat shield
Yup, that's exactly what I thought too! The stock airbox gives a lil more low end torque in my setup. Had a GruppeM before and I sold it, put back my stock airbox w/ K&N filter. The car pulls alot better on the lower rpm, but I can feel that it kindda hesitates in the mid-to higher end of the rpm range. Im plannin on putting a GruppeM back, and to eliminate the low end power loss, thinkin of gettin a more aggressive diff.
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Old 08-27-2006, 10:21 PM   #17
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First of all, the "flap" on stock exhausts have nothing to do with backpressure. They are simply there for noise reduction. Anyone who says they have noticed torque loss from disabling this flap is simply talking out of their ass.

The whole idea of putting on a high performance exhaust is to achieve large horsepower gains. The drawback to this setup is that you will lose some low-end torque. What you need is a high performance intake as well. Not only will you see the additional benefits of increased horsepower due to the free-er flowing exhaust, but the additional flow of air will result in more air having to be exited from the combustion chamber, thus increasing back pressure and gaining back some of your torque.

As for someone who said that you need a new fuel mapping; this is not necessary. The onboard computer will automatically adjust the fuel/air mixture accordingly, just as it does with BMW's own throttle adaptation program. Unless you install larger injectors or something like a supercharger, there is no real need to adjust the computer to benefit from the aftermarket intake/exhaust setup as the car does it on its own.

This bring me to another topic... those who put on aftermarket intakes without installing an aftermarket exhaust. Just like humans... cars breathe in, and breathe out. You can only "breathe" as well as you can do both. If you increase your ability to breathe in (aftermarket intake), but do not increase your ability to breathe out (aftermarket exhaust), you will only see minimal performance gains. Improving the entire "flow" of the system, i.e. intake through exhaust is the key to truly improving overall performance while maintaining a balance of low-end torque/high-end horsepower.
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