My Dealer says my Louth Mouth mufflers don,t have enough back pressure. I have not touched the rest of the exhaust system. Said back pressure caused a miss fire at different RPM's. I took the car in because it was missing a 45 MPH in four gear.

Help Is he right ,wrong, or don't worry about it.

Thanks
George
Ft Sill OK

2012 GS 6speed. 7K miles Blue

 

Sounds a little rediculous.

 

It's scary he actually thinks that and advises others on automotive issues...

 

I've never heard of any crap like that. I think you need to find a new dealer.

 

Moron stealership. They will say anything to get out of warranty work for some reason. Not sure why? I have heard similar things from my dealer regarding my last C6 that has B&B bullets on it. I had an annoying interior rattle on the dash. After it being in their service department all day, I was called to come get it and it was done. When I asked what they fixed, they said nothing. They claimed the axleback exhaust was causing the rattle, and they would do nothing until I put the stock mufflers back on and to bring it back. Took them 8 hours to come up with this "diagnosis".

I did, the rattle was still there and they fixed it. Then I bitched to the service manager and the owner, and they agreed it was stupid to blame the exhaust for the dash rattle and gave me a years worth of free oil changes. I declined them because I normally change my own oil. That was a happy story. I have a few that were not nearly as happy.

 

Yes, that is a stupid excuse.

 

Thing's like that and the OPs problem are a pain in the *** to diagnose, and the dealer is probably only paid an hour or two by chevy for it, so they try to make it a pain for you to change the exhaust out and come back because it just doesn't pay.

It's also a pain in the *** for independents as well, you come in with misfires not caused by one of the usual suspects. After being billed a few hours running through the usual suspects like plugs and coils, being told you are looking at an even bigger bill to go through other possible causes, you're probably already pissed and direct that anger at the shop and their reputation. Now if after 10 hours some vague crappy cause is found and fixed and you pay your $1k bill, you will curse the shops reputation every chance you get.

So you really need to go a mile in a shops shoes before you bitch and moan over what they do.

 

Thanks for the info

 

I really doubt that mufflers alone could make enough difference to cause a misfire. At the same time, there is a general feeling here on the forum that more (or less in this case) is always better, and this is frequently wrong. Z06 suspension pieces are too stiff for a car with base sized tires. More stiffness is not better in this case. Less restriction is not always a way to more power from an engine. There is a reason that the LS2 and LS3 engines are not paired with the three inch exhaust system from the LS7 and LS9. A certain amount of backpressure is needed to properly scavenge the cylinders which provides more low end torque. Again, more decrease in backpressure is not always better.
I think it was LG that said that as a general rule, any mod between the MAF sensor and the last O2 sensor will require electronic retuning of the car, and any mod in front of the MAF or after the last O2 sensor can be compensated for by the computer without tuning. I think this is a good general rule.

 

This is not correct, it is never correct. No engineer in the building of a four stroke exhaust has EVER gone "oh jee too little back pressure, I better bump that up some"

It's true that sometimes an exhaust with "higher" back pressure might make more power, but it has NOTHING to do with the higher back pressure and everything to do with exhaust tuning. An engineer will always shoot for the lowest possible back pressure he can achieve within the constraints of other variables.


Please let this fable die already.

 

I disagree. If that was true, then every engine would have huge exhaust pipes to minimize backpressure, or no pipes at all. The size and configuration of the exhaust system must be matched to the engine to get the right amount of backpressure. This is why the LS2 and LS3 have smaller pipes than the LS7 and LS9. This is also why headers are made in different tube diameters and heads have different sized exhaust ports etc. Bigger is not always better.

 

Unfortunately you obviously didn't comprehend what I said, either didn't try or incapable. Even If I explained it to you in agonizing detail, I don't see one person convincing you, and from what you wrote you obviously don't understand what you're talking about.

 

Fair enough, I'll agree to disagree with you, and not get into whether I'm capable or trying

 

I'm with BoosterClub on this one. the max HP engines have super short huge exhaust pipes on each individual cylinder and three 90mm bug catcher intakes. No back pressure but huge HP.

The exhaust size and routing is cost, weight and location driven, not amount of back pressure required.

The engine is basically an air pump, the easier to pump air in & out the better.

 

OK, but lets take the LS3 as an example. If it was just "bigger is better", then Chevy would have just put the Z06 exhaust system on it and gotten more power from it, but they didn't. The reason is that a bigger exhaust system would have lost them some low end power and made the engine less driveable at lower rpm. The LS7 is a bigger air pump, needing bigger tubes. This is also the reason that they have the NPP mufflers open at 3,500 rpm, to allow for a bit more backpressure at low rpm (better driveability) and then less at higher rpm (more peak horsepower). We have all been in a car where the owner has put in a cam that was way too big...I saw lots of these when I was a kid. The thing would scream at 6,000 rpm but when you were at 1,500, it had far less power than it did when it had its' original cam from the factory. It's a compromise that must be made...bigger ports, cam, exhaust etc for top end power, against smaller for low end driveability. If not, then everyone would be making headers with three inch tubes...after all, less backpressure. Header tube sizing is very important for just this reason.

 

Again, no engineer EVER said "we need more back pressure" it has nothing to do with back pressure and everything to do with exhaust tuning. Just because two things sometimes correlate does not mean they are the cause, and in this particular case, it's not even a strong correlation.

Do yourself a favor and read up on scavenging and exhaust velocities. I hope you don't need a hint on what won't be talked about being beneficial.

 

The misfire isn't the result of the exhaust.

But to the other part about the back pressure. This is a yes and no answer. Engines have been known to suffer from low end response and power/torque due to oversized exhaust pipes, WHEN NO OTHER CHANGES HAVE BEEN MADE. When tuning changes are made the resultant loss can be mininmized or eliminated. I'm not talking about headers... I'm talking about exhaust pipe diameter.

 

Thak you all for the Quote's. So I will take one muffler off and leave one on. No I have learn alot here, back is needed how much is the question. I am going to hit up Loud Mouth people and see if they will giveup an answer.
Thank you for your notes

 

If you are saying that you will keep the muffler on one side but not the other, that is not a good idea. The two sides of the exhaust system must be the same..balanced....if I am understanding you correctly?

 

I would happen to agree with BoosterClub, haljenson and glenB. The backpressure is required argument is completely wrong.

Part of the exhaust tuning is building a certain flow velocity, which is important in the primaries of headers. There's a good reason they aren't 3" in diameter - it's because it would kill the flow velocity which kills the scavenging of the cylinder. If possible, we'd all want the correctly size pipes to tune the flow and scavenging which are built from unobtanium which has no restriction to flow.

Next will come that stupid story about the old Harley with a bolt and washer welded into the pipe to tune the back pressure on the fly for switching between driving light to light or tearing down the highway....

A55Chev - you might have to change them back to get the crappy dealer to actually fix it, but the mufflers aren't the problem.