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Old 06-01-2001, 02:56 PM   #1
trojan9x
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Question What causes exaust "POP!"

seems like whenever i let off the gas while slowing down the car sometimes lets off little "pops" or gurgles, then when i take off again, it sometimes "pops" as soon as i press on the gas. What would cause this?

TNN...got POP! my exaust does
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Old 06-01-2001, 03:04 PM   #2
CSM101
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Unequal length header plus close coupled cat equals "POP"

It's from unburnt gas hitting the converter.
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Old 06-01-2001, 03:52 PM   #3
Blindeye_03
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I laugh my @$$ off every time i backfire and pop my exhaust. Its sooo loud with the N1 canister.
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Old 06-01-2001, 05:54 PM   #4
cvalle-sd
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too many corn kernels in the headers.
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Old 06-04-2001, 07:49 AM   #5
Chuck
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I don't think unequal headers or closely coupled cats have anything to do with it. I have equal length headers and a single cat, and my exhaust still pops and gurgles. It's a long Subaru trait. I believe it's from our engines running more rich than other brands, which means more unburnt gas in the exhaust that explodes when it hits other hot things.
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Old 06-04-2001, 09:47 AM   #6
ChaosThom
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There are two common reasons:
1) The exhaust isn't properly tuned -read correct flow- to the engine.
2) The car is running too rich and unburnt fuel is igniting in the exhuast.
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Old 06-04-2001, 10:21 AM   #7
Grap
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Also if you have any leaks, the leak allows oxygen into the exhaust which = Boom!
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Old 06-04-2001, 10:23 AM   #8
AdidasCU
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It used to happen on my Jetta a lot. I think you can hear more of what is going on in the engine when you open up your exhaust. It did it onmy Tahoe this weekend too
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Old 06-04-2001, 03:16 PM   #9
STiTuner
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so is there any way to prevent something like that? My car with my intake and exhaust sounds like a bag of popcorn when using the engine to slow down.. will a TecII allow you to gid rid of that? or is this something I will have to deal with even after my turbo goes in?


Brad
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Old 06-04-2001, 06:24 PM   #10
SuBart
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Why would you want to get rid of that. Thats one of my favorite things about my car. Haven;t you ever seen a rally car in action, its all they do is "POP". Gotta love it.
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Old 06-04-2001, 09:18 PM   #11
Rubr_Duky
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The rally cars pop intentionally...

It's a design that they developed to keep their turbo spooled, they make the off throttle deceleration air/fuel mixture intentionally rich, which when exposed to the turbo, explodes, forcing the turbo to keep spooled, and the turbolag to a minimum.


RD
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Old 06-05-2001, 12:13 AM   #12
pottsie350
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Just about every engine I've heard has an off throttle rich condition when you use the engine for braking. The Subaru shuts off the fuel injectors after decelerating for more than a a couple of seconds. So you'll get the burbling or popping when you first let off the throttle completely, then as you gently add the throttle and the fuel injectors start injecting again it will burble or pop a bit more until the engine is no longer decelerating. It's unburned fuel in the exhaust manifolds, being reignited by hot exhaust gases.
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Old 06-05-2001, 05:39 AM   #13
pottsie350
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I believe with a tec II you could minimize the popping. You can control how quickly the fuel injectors shut down on off throttle. I don't think you could completely eliminate it. But I'm no expert on the tecII. I know that fuel injectors have a stall limit, The point where the signal is so weak that the current can't over come the mass of the valve and spring in the fuel injector. The fuel injector therefore has a minimum guaranteed fuel flow before it shuts off completely.

I would think that if you were to cut down the fuel flow shutoff time out under deceleration, you could run into stalling problems if the system reaction time were impeded for some reason.

Another note, the Tec II is supposed to be better at driving the fuel injectors than the stock ECU. It may have better resolution and be able to achieve lower fuel flow. Just guessing here. Post on http://www.vishnuperformance.com somebody there should be able to answer tha question.

I personally think the popping and burbling is cool. It reminds me of the carbureted days of racing. And of the rally cars running rich off throttle to keep the turbo spooled up. I like it much better than monotonous drone of an engine decelerating with no fuel... That has no character. Pops and burbles add character and get the blood flowing.
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Old 06-05-2001, 09:45 AM   #14
Mr.Preza
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HEHE.......I make it "pop" and "burble" on purpose! Gotta love the Subie!
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Old 06-05-2001, 01:21 PM   #15
trojan9x
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wow, thanks for all the responses...i thought i did something wrong when i installed my exaust. no leaks, but popped. now i know it isn't my fault...it's my car's fault. my car farts more than i do
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Old 06-05-2001, 07:48 PM   #16
RaceCarRiot
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pop go da weasel cos da weasel sez pop!

flat engines also just seem more susceptible to this. my bug did all the time it once i got the roadracing exhaust on it...then again having a car old enough to be street legal with no pollution controls helps as well. boy i miss that car...except for having it towed to the mechanic weekly. my dad's BMW motorcycle does it as well on occasion (2 cyl boxer engine).

anyone figured out which exhaust system leads to the most popping and flame throwing yet? it may greatly influence my purchasing decision. or are us 1.8 owners out of luck?

(adam)

[EDIT] grr. been at work for 12 hours. can't spell.

[This message has been edited by RaceCarRiot (edited June 05, 2001).]
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Old 06-05-2001, 08:15 PM   #17
Rubr_Duky
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I think it would be really difficult to do any such flame throwing with a 50 state leagl exhaust.. remember, most of the country is covered with this stuff called "PLANTS" that typically burn when exposed to fire.. that would be bad.

I would imagine that ther larger the exhaust pipe in diameter (while retaining length) would lead to the most popping.. my 87 Nissan P/U did the same thing when I installed a 2.25" cat-back system.. that was only 1/2" up from the 1.75 system it had, but BOY what an improvement, and Oooooohhhhh the "POP"s.


RD
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Old 06-05-2001, 08:34 PM   #18
STiTuner
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RaceCarRiot:

WR Sport Exhaust + 3in Intake + 2.5in Straight intermediate pipe =

BAG OF POPCORN IN EXHAUST AND NO GAS MILAGE AND CEL.. wait the CEL is gone now.

Is there anyway to keep the fart and burp (other then self generate it) and keep good gas milage. I know that my car smells like a gas station after driving sometimes. Atleast my burps and farts won't make me pass out.. well most of the time anyway

Brad

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Old 06-06-2001, 05:11 AM   #19
RaceCarRiot
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Quote:
remember, most of the country is covered with this stuff called "PLANTS" that typically burn when exposed to fire.. that would be bad.
hey, you don't have to tell me that...i'll just be doing my part to contribute to the burning of florida! look out southern california...we've got your number!

(adam)
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