Just picked up an 09 cobalt ss and I was talking to a friend that also has one. He works at a performance shop and said that when they cut a muffler off one, it lost a bunch of torque. I work on a bunch of turbo cars and usually tthe less restrictive exhaust the better. So I went to the shop today and cut the muffler off and he was right, feels like it lost 30 ft. Lbs! The car is all stock and I plan on tuning it very soon. I love the way it sounds and wanna leave it that way. So here are my questions

1. Why did opening the exhaust decrease the torque?
2. What can I do to get it back?
3. Is it better to have a full 3" exhaust when tuned or is the stock exhaust good enough?

I'm just confused, never thought it would affect it that much. The car isn't that fast stock but it's still a little fun. Not as much fun now!

Thanks for the input!

 

you prob lost at least 60..

 

thats like saying a muffler can give you 60. . .

 

I definately thought he was full of **** when he said it'd lose torque. Is it the "learn down" that's making it do this. Only making 13.9# of boost since, before it'd make 15.9# or so

 

Really !! It can't.. So my 8" tip fart can didn't give the 50 hp it said ? Hmm..

 

It's in your head OP or something else is wrong with your car.

 

A muffler delete cannot cause you to lose power.

 

never heard of such a thing

 

Answer #1) Its a common misconception that removing all backpressure gives a total increase in power. I have dynos for a bunch of cars, mostly V-8s, that I have built that get less torque without backpressure. Do you have a cat-less d.p.? Generally speaking in cars with smog restrictions and stuff there isn't a whole lot of backpressure behind the cat(s). Tuned headers and cat backs are better at using exhaust pulses naturally generated by your engine to scavange burnt air/fuel mix out of cylinders.

2) If you want to muffler delete the best idea would be to keep the correct length of exhaust all the way back to the bumper at the very least. Your best option is to put a 3" system on there. Although I think it probably has more to do with the lenght of the exhaust rather than the lack of backpressure

Thats just my .02 from my past engine buiilding experience. Good luck with your car.

 

This is true in NA or SC applications, since the exhaust is right off the headers and valves. In a turbo application the necessary backpressure is before the turbo, so changing a downpipe/catback will/should only result in gains.

Most likely it's the learn down letting you know it's not happy.

 

I know it sounds crazy...but it's not in my head. it's definately down on power. It's gotta be the learn down taken 1-2# of boost out. Like I said I just got the car and it usually makes close to 16# and last night it was only makin around 14#. I was thinkin maybe they weather was the cause of the drop in boost but doubt it. The exhaust is very close to the same length as stock, within an inch, so I wouldn't think that could cause it. I should have put it on the rolls and made a baseline then put it back on after. But that was just way to much work by myself! Plus I was in a hurry to get down to woodward and watch some cars! Guess I'll have to tune right away. Good thing I have access to a free dyno and hp tuners, just have to pay the $100 license fee...and someone to help me with the tune. Never done anything direct injected

 

Also, boost psi does NOT necessarily mean more power. It's air restriction. A hi flow exhaust (i.e. muffler delete) will creat LESS psi since there is LESS restriction.

 

If it's down on power, something else is wrong. I have a MD too, and my car is just as powerful as it was before.

 

What? Are you serious? The stock Muffler on this car is straight through it should not add any power to remove it but it should also not cause power loss either.

 

Ummm, no. If the perf. shop says it'll lose power go somewhere else.

 

just tune it. you'll get it all back.

 

Yes i'm serious it prob lost 1000 hp.. A good tuner should know that.

 

Same here feels the same as before,but sounds a lot better

 

I have the opposite effect it feels like my turbo now spools slightly faster with the muffler delete, maybe its the slight increase in sound but it sure feels like its just a hair faster than before, I didn't do a muffler delete for power though I just like the sound

My boost is exactly the same now as before spikes at 24 holds 22

 

The car is making the same power on less boost. You should be pushing the same amount of power.

 

I understand that boost is just a measurement of restriction, like I said before I've done a lot with Turbos. Most of the reason I got the car...daily with good gas mileage and a turbo! But if the pcm "learn down" is taking out 2# of boost...that will for sure result in a loss of torque. From what I understand with very little reading, the learn down basically tries to keep the engine makning the same power as stock. To adjust for changes in air which would produce more power. Correct me if I'm wrong?

Nothing's wrong with the car. I beat on it all the way to the shop, cut the muffler off and beat on it again. Definately different.

I only did the muffler delete for sound , not for a power gain. It does sound really good. This is coming from a die hard v8 guy!

 

in my personal experiance the dumb asses that cut their exhaust off to make it louder or for what ever reason, causes the car to lose back pressure. it will kill horsepower and torque and it will royaly **** your car up in the long run

 

Except this is a turbo engine, the more free flowing the exhaust is the better, That's why these cars love catless downpipes

 

but still if there is 0 back pressure wouldnt that be bad? i mean yes less restrictive would be the more the merrier but 0 would be bad right?

 

An engine is nothing more than a glorified air pump more air out means more air in which means more power. Engines do not like back pressure at all. There are slight lowend torque gains that can be provided by scavenging of exhaust gas but this mainly applies to naturally asperated (well non turbo anyway) engines. Back pressure is bad but so is low exhaust gas velocity at lower RPMs.