2008 Impala LS Homemade Dual Exhaust?

35

Asked by 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

220

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...

1 of 1 people found this helpful.
10,645

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.

35

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?

35

Just without the cats on both side?

220

If you are leaving the mufflers on thats not straight pipes

1 of 1 people found this helpful.
35

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

1 of 1 people found this helpful.
220

Define work? What are you trying to achieve?

10,645

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.

220

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

1 of 1 people found this helpful.
10,645

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.

220

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

425

back pressure is a myth and o2 sensors dont read it

1 of 1 people found this helpful.
220

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 of 1 people found this helpful.
Best Answer Mark helpful
10,645

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.

1 of 1 people found this helpful.
7,625

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 of 1 people found this helpful.
10,645

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.

220

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

19,745

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.

7,625

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 of 1 people found this helpful.
10,645

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.

7,625

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?

425

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

1 of 1 people found this helpful.
10,645

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).

425

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

10,645

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.

425

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

10,645

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..

425

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 of 1 people found this helpful.
7,625

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

425

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

10,645

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?

10,645

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.

7,625

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.

7,625

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.

19,745

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 of 1 people found this helpful.
425

Andrew, I couldn't have said it better myself

1 of 1 people found this helpful.
220

Thanks Andrew for shutting them up!!!!

1 of 1 people found this helpful.
10,645

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..

35

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

16,455

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.

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