2008 Impala LS Homemade Dual Exhaust?

Vince08
25

Asked by Vince08 Oct 02, 2012 at 11:46 PM about the 2008 Chevrolet Impala LS

Question type: Car Customization

So I was thinking about rigging up my own dual exhaust. Just cutting off the exhaust where the headers meet
and then using a Y pipe to break the exhaust off to each side with a muffler on each side. I talked to a couple
people about this, and they said something about how my car wouldn't have enough back flow through the
mufflers and it would actually decrease performance and It wouldn't sound good at all, but then others said It
would work and would sound good. I'm not sure if anyone's actually done this themselves and they could give
me a rough idea on if it's a bad idea, or how to do it right.             Thanks.

40 Answers

nater_
160

Ive done this several times never on a car but several trucks yes you do lose much needed back pressure but i compensate for that by welding a few pieces of angle iron or tubing to make up for the resistance the muffler would normally create...

Michael McGrail
5,415

Most FWD cars have a single pipe cavity under the car. Running duals would involve running a pipe outside of the cavity creating a ground clearance issue. When I had my GTP, I installed a set of headers, a high flow cat and used a larger diameter pipe that ran the length of the car to the muffler, then split out of the muffler for the dual look. Running true duals was just not an option as I did not have the room for it.

Vince08
25

What I don't understand is that if I did straight pipe it, I would have mufflers on each side, so would that still effect the back pressure?

Vince08
25

Just without the cats on both side?

nater_
160

If you are leaving the mufflers on thats not straight pipes

1 out of 1 people think this is helpful.
Vince08
25

But if I just take the catalytic converters off and keep mufflers on, will that work?

nater_
160

Define work? What are you trying to achieve?

Michael McGrail
5,415

For your o2 sensors to read correctly, you will need to keep both your mufflers and your cats. Removing one or both will cause more harm than good.

nater_
160

How will removing the muffler effect the 02 sensor if the sensor is in front of the muffler ?

1 out of 1 people think this is helpful.
Michael McGrail
5,415

In an obd2 system you have both before and after cat O2 sensors. Mufflers maintain a certain back-pressure that is needed for the after cat O2 sensor to read correctly.

nater_
160

So you saying that the 02 sensors can tell the difference in back pressure from a muffler and back pressure from restricter tubes?

Devin Woodworth
365

back pressure is a myth and o2 sensors dont read it

1 out of 1 people think this is helpful.
nater_
160

Thought this sight was about helping people whats your problem? Who cares what kinda car it is its his car he can do what he wants to it kewl you a moron!

1 out of 1 people think this is helpful.
Best Answer
Michael McGrail
5,415

No.. The O2 sensors do not read back pressure.. But they do read various hydrocarbons. If those are weakened by the loss of a cat or muffler then the sensors do not read correctly. They try to over or under compensate for the variances by reducing or increasing fuel to adjust the air/fuel mixture to what the computer was programmed at.

Chase Sutherland
3,975

michael. the 2nd set of O2s dont do jack. they basically tell you if your car is running ok or not by measuring whats coming through the exhaust. if the cat isnt doing enough or if its doing too much they throw a code. they dont control how the car runs. thats the front O2. without a cat you will throw a CEL without getting a proper tune. my suggestion...increase the size of the piping you run by 1/2" from the cat back and throw on a different high flow muffler. in your case a flowmaster will work sut fine for a little more rumble. youre not going to gain any extra performance without doing headers and getting a tune anyways so keep the CEL light off and car running nicely.

1 out of 1 people think this is helpful.
Michael McGrail
5,415

Unplug the rear o2. Tell me if you just get a code or if the car starts to run like crap. You can get O2 simulators to in essence bypass the rear sensor. We installed them in my brothers Formula when we went with the much larger exhaust (with exhaust cut-outs) because it kept tripping the CEL and his car would start running like crap. If the O2 sensor is not reading correct (before or after).. It will effect hp, performance and gas mileage. The more extreme the readings, the more the computer makes adjustments. Now will removing the mufflers on this car cause a similar issue.. Dunno, with such low HP, prolly not to that extreme, but it will almost certainly trip the CEL.

nater_
160

Vince if you want dual straight pipes run them chop off the mufflers weld some tubes inside the pipes for resistance and your car will run fine without a check engine light ive done it over and over you wont any noticeable power increase but you will get a great tone

Andrew Olsen
6,165

running duals on a car that uses o2 sensors that isnt designed to have duals can have negitive performance affects. Just have a single in dual out muffler. Looks the same, still sounds good and performs better. I've seen 2 2000 model mustangs race 1 with dual exhaust v8 and the other a stock v6 and the v6 mopped the floor with it. I didnt know the mods on the v8 other than the exhaust but the v6 was my cousins and it was completly stock to the air filter.

Chase Sutherland
3,975

Michael...unplugging them isn't the same thing and you know it. Getting a zero voltage reading will clearly mess with the car. I run long tubes with no cats on my gto....front O2 was messed up and it ran like crap. Fixed that and it runs great. One of the rear O2s is bad and the car runs perfectly fine. Makes no difference.

1 out of 1 people think this is helpful.
Michael McGrail
5,415

Chase, what is your scanned readings/ratios from the O2 sensors? I am sure the removal has them way out of spec. So much so, I am surprised that your CEL was not tripped. Your PCM calculates so many different factors and most people do not realize that altering something like (removing cats or hollowing them out) can cause the computer to read intake and exhaust out of spec and start altering settings. Removing a modern catalytic converter in new condition will not increase vehicle performance without retuning. You can reprogram a PCM to ignore it, but due to the fact that is is illegal in the U.S. to remove a cat except for a direct replacement, most will not retune. There are O2 deletes (simulators) that will trick a tune into thinking everything is ok, but they only work for the rear O2s.

Chase Sutherland
3,975

michael....i have my car tuned and the rear O2s are simply turned off. the car reads nothing from them. if they actually did anything that delt with fuel management this wouldnt be possible. but if i unplug them i throw a code and the car runs like crap. its because of the circuit. cant leave it open. and let me ask you this....if the rear O2s did anything why are you able to "trick"your car into "deleting" them and have it run fine?

Devin Woodworth
365

Brain explosion from the amount of stupid going on in this thread

1 out of 1 people think this is helpful.
Michael McGrail
5,415

Basic computer programming Chase. Basic computer programming... Simulators trick the computer into thinking the sensor is reading correctly. Same way in which you had your PCM reprogrammed. The sensors are not turned off, the signals have been rerouted to make the main program think the sensors are there and working correctly (kind of like adding a virtual drive to your computer.. Not actually there, but can be used to mount ISO images).

Devin Woodworth
365

all the post-cat sensors do is make sure the cat is still there and working correctly. the only reason there are trick programs for them is because people like to take out their cats and still be able to pass inspection and it has nothing to do with performance. if you have a running like crap issue from a bad post-cat o2, you're looking in the wrong place

Michael McGrail
5,415

If you run an O2 simulator. You will not pass an emissions test. The test is run off of the exhaust gas.. Removing equipment or sensors from the emission system will most definitely cause you to fail. Those tests are so sensitive that old spark plugs can also cause you to fail them.

Devin Woodworth
365

wrong again, with the exception of california, no other state runs 5-gas tests anymore. all they do to inspect the vehicle is plug into the OBD-II port to make sure all the sensors are reading within specified ranges, one of which being the post-cat o2 sensor. thats where the simulator comes in, it tells the ECU that the sensor is reading correctly therefore the cat is functioning properly, even if there isnt actually a cat there. go elsewhere and fail some more

Michael McGrail
5,415

I was making my assumption off of California as they are the only ones that do an 'emissions test'.. I lived there for a few years. Other states merely do vehicle inspections and each state is different on what they check for in the inspections. Here in Texas and Louisiana They mostly just make sure the lights and seatbelts work.. Maybe you should go somewhere and fail Devin..

Devin Woodworth
365

see thats where your problem is, you made an assumption. try getting facts instead, or better yet, stay in the south and continue failing. you can go ahead and tell me to fail all you want, but in the end i know more about the subject and automotive in general

1 out of 1 people think this is helpful.
Chase Sutherland
3,975

devin...thank you for the backup on the rear O2s.

Devin Woodworth
365

chase, you're welcome. i've gone to school for all this and worked in automotive for years and it pains me when i see people spewing incorrect information. just gotta stand up for the truth

Michael McGrail
5,415

You guys are wrong about the o2 sensor. And Devin, I love the comment that everyone give "i've gone to school for this" I love it.. I find it entertaining.. Most of the time it is a crock.. It is usually just some guy that worked on his car once or twice. As for me. I obtained my ASE certification in 2002. I have personally reprogrammed an ECM/PCM. I have plenty of experience in electronically controlled vehicles and transplanting LT1/LS1 engines into various older vehicles. Chase, you said the rear O2 does nothing but you bypassed it. Devin, you apparently are a troll. Personal attacks on me orhhte South is uncalled for. I corrected you on the fact that the car would not pass emissions. You have no clue where this kid lives (assuming kid as not rational adult would want to do it). He very well may live in Cali. Out of curiousity.. Have either of you ever taken the time to actually build a car? Chase I know you took your car somewhere.. But how about you Devin?

Michael McGrail
5,415

Nevermind.. Don't answer that.. I just realized that the guy that started this thread is a few cents short of a full dollar as he has opened a couple other trolling threads. You guys have fun.

Chase Sutherland
3,975

built my 87 iroc (first car) and now i do all the work on my gto (except the tune because i dont have the software or a dyno). the rear O2 simply tells you if your cat is working. fuel trims are adjusted by the front O2 sensors. after time goes by cats go bad right? that would continually change the rear O2 sensors output to what fuel to deliver even though the engine is still running the same....how does that make any sense? you measure and calculate fuel delivery before the cats (front O2s). not after.

Chase Sutherland
3,975

devin...hey now lets not bring the ls1 into this. thats a damn good motor. lets keep the focus on the guy whos feeding false info lol.

Andrew Olsen
6,165

Here's the deal, front o2's deal with the cars fuel air mixture, it's constantly bouncing between rich and lean. That's how it keeps a proper mixture. If this one fails it throws the whole system out of whack. The post cat (rear o2's) detect how efficient the cat is. The number should be fairly constant and low, if it fluctuates then it throws a code becasue that means the cat isn't filtering. under normal operating conditions there is no way the rear o2 can adjust anything because the reading should stay constant. If the sensor itself goes bad the car will run the same just with a CEL. You wont pass emissions. If it throws a code becasue the cat is clogged then it will run bad but that's becasue of the cat. I'm sorry bro but the rear sensors dont adjust the fuel trim or anything about the running of the car. Tuners will delete the rear o2 from the system so they can run no cats and cheat the emissions tests. Illegal but other than California they wont notice because they arn't usually looking. I'm refering to Georgia emissions laws, lots are similar. Dont mock someone for going to school when they are right and you are wrong. To think, all this poor guy wanted was to ask about running duals on his Impala. Still dont agree with btw.

1 out of 1 people think this is helpful.
Devin Woodworth
365

Andrew, I couldn't have said it better myself

1 out of 1 people think this is helpful.
nater_
160

Thanks Andrew for shutting them up!!!!

1 out of 1 people think this is helpful.
Michael McGrail
5,415

With the introduction of OBD2, most vehicle manufacturers started using a wideband type O2 sensor (air/fuel ratio) in the front position for better engine control. These wideband type sensors need to be recalibrated from time to time by the ECU. The ECU uses the rear sensors for this recalibration process. This is how the system counterbalances itself. When a fault is detected the PCM uses the most recent reading of the system and locks the system down into a closed loop mode (which means no further readings are taken). This is why on most manufacturers you have to clear the code after you replace the part so that it starts reading everything again. There is a big difference how a 1995 obd2 system and the newer obd2 systems monitor. There is a lot more capabilities within in the newer PCMs for adjustment and tweaking as well. I fully understand what you guys are saying, and we are all pretty much on the same page. And as I mentioned before it may affect it.. It may not.. With the low HP rating.. Prolly not.. Of course running duals are not going to help it any either..

Vince08
25

Trolling thread? I was actually planning on doing it depending on what kind of advice I got, but that didn't go very well.

califcarson
3,755

I'm a V-8 person myself. Well let's say an older car V-8 man that feels the sound is lovely music. Duel exhausts with or without mufflers or cats does not do it for me in the sound category on a V-6 or straight 6. If you want sound and more power, just slap your forehead and say, "I could of had a V-8". Either sell the car, or drop in a small V-8 with a good cam in it. Unhooking the cats or removing the mufflers will also trip the ticket book of your local law enforcement officers. In California there are sensors that sniff cars and take pictures of cars on the highway that give off more than normal levels of pollutants. Then you get a letter telling you to go to a smog station for testing.

Your Answer

Add photo

Related Questions

  • Dual Exhaust upgrade? 3 answers

    i Drive a 2003 impala Ls and want to put dual exhaust on it. is there any cars around that year with duals that would fit this? im asking cause i dont wanna spend lots of $ on custom exhaust. hoping i...

    2003 Chevrolet Impala LS

    -

    Car Customization

  • Aftermarket Air Intake? 2 answers

    A couple guys I know have basically rigged up their own air intakes and I'm considering doing the same on my Impala since it would be about 200 dollars cheaper. Basically taking out the stock intake a...

    2008 Chevrolet Impala LS

    -

    Car Customization

  • I want a muscle sound for my 01 impala 3.4, what would be a good exhaust choice?? 5 answers

    2001 Chevrolet Impala

    -

    Car Customization

  • 1994 Impala LT1 1 answer

    Have a friend with 1994 Impala with 350/5.7L and 3.73 rear end for more torque. Besides all upgrades K&N Intake etc...... how can I boost more performance out of this baby? Dyno and re-flash PCM is do...

    1994 Chevrolet Impala

    -

    Car Customization

  • 84 Impala 1 answer

    also anybody know if the 84 3.8 came with duals, when I got it only had one but was missing an entire exhaust pipe had to change the manifold now im still looking for a pipe where can i find a used on...

    1984 Chevrolet Impala

    -

    General

Impala
Looking for a Used Impala in your area?
CarGurus has 57,969 nationwide Impala listings starting at $990.
ZIP:

Search Chevrolet Impala Questions

Chevrolet Impala Experts

#1 Danny Wang
Danny Wang
Reputation 980
#2 Tom Demyan
Tom Demyan
Reputation 680
#3 Justin Hatfield
Justin Hatfield
Reputation 630
View All

Related Models For Sale

Used Chevrolet Malibu"
1,834 Great Deals out of 71,726 listings starting at $855
Used Dodge Charger"
786 Great Deals out of 30,964 listings starting at $2,950
Used Honda Accord"
1,450 Great Deals out of 64,077 listings starting at $1,089.41
Used Nissan Altima"
1,846 Great Deals out of 78,350 listings starting at $1,495
Used Chevrolet Monte Carlo"
62 Great Deals out of 2,422 listings starting at $1,595
Used Toyota Camry"
1,927 Great Deals out of 69,771 listings starting at $1,395
Used Nissan Maxima"
690 Great Deals out of 19,476 listings starting at $1,499
Used Ford Mustang"
1,059 Great Deals out of 25,034 listings starting at $1,625
Used Chrysler 300"
729 Great Deals out of 21,079 listings starting at $2,500
Used Ford Fusion"
1,984 Great Deals out of 68,739 listings starting at $2,500
Used Ford Taurus"
698 Great Deals out of 18,983 listings starting at $800
Used Dodge Challenger"
357 Great Deals out of 18,412 listings starting at $11,497
Used Buick LaCrosse"
510 Great Deals out of 24,731 listings starting at $2,800
Used Chevrolet Tahoe"
1,057 Great Deals out of 33,045 listings starting at $2,495

Used Cars For Sale

2014 Chevrolet Impala LS For Sale
99 Great Deals out of 3,963 listings starting at $12,999
2013 Chevrolet Impala LS For Sale
43 listings starting at $12,978
2012 Chevrolet Impala LS For Sale
4 Great Deals out of 111 listings starting at $9,400
2011 Chevrolet Impala LS For Sale
6 Great Deals out of 145 listings starting at $5,900