and the car sounds great. it had a 3 in down pipe and a 2.5in gm performance exhaust system but it just didnt make any noise so I was convinced to delete the muffler and it sounds deep, rich, and just loud enough to sound good but avoid tickets.....

but would this change my car enough to lean it out without a proper tune?

I have a zzp pcm on the way, I tracked it and its due at my house tomorrow evening so thats on my agenda tomorrow night!

 

Won't change the tune a bit.

 

sweet because i was just concerned about it leaning out since I have no air/fuel gauge

 

There's a built in wideband and the car runs in closed loop almost all the time.

 

how would the car run lean from deleting the muffler? I really interested in the theory

 

^ Why wouldn't the car run leaner? I would think it would due to better scavenging.

 

GMPP exhaust for LNF? did they make one?

 

I don't think the made one for the turbo balt.

 

Post turbo exhaust leaks do not affect performance. The piping is really only there to route exhaust fumes out the back of the car, you could run open from the downpipe and be fine (noise level/fumes not withstanding).

Muffler delete's / "hogzaust" (which is essentially an exhaust leak right before your muffler) are fairly "common" among the Subaru community, never heard of anyone doing it on a Cobalt, but would be interested in a soundclip/vid of the results.

 

After a turbocharger nothing really scavenges turbos cause backpressure and there are no exhaust pulses to be utilized.

 

Every car creates back pressure, some exhaust systems create more than others, hence why the call flowmasters choke masters. I did not know a turbocharged car doesnt produce exhaust pulses, wouldnt everycar produce that? Cylinders are still firing and making a pulse.

 

A muffler is put on a car to make it quiet. I know they sell "performance mufflers" but really all they do is make the car louder than stock. Depending on how big it is, shape, how they pack it, baffle materials and so on affects the sound. Think about drag cars, do they use mufflers? No, for a better flowing exhaust

 

You generally experience NO gains on most modern cars from simply removing the exhaust. I'm not sure which drag cars you are referring to. There's a reason why cat backs generally net very little gains and turbo-backs net quite a lot, the downpipe is the restrictive part, once that's removed the turbo can breathe more efficiently. Unless the muffler you've on your car is extremely restrictive, you won't see any gains from this alone.


N/A cars need exhaust velocity to assist with scavenging. Backpressure is an *unwanted* bi-product. If the exhaust in an N/A car is too big you lose exhaust velocity, to get the correct velocity you need to lower exhaust diameter, which causes increased back pressure.

You can basically throw this all out when you start talking about turbocharged engines.

Turbocharged engines do not rely on exhaust scavenging, it is more beneficial to just get boost sooner, the benefits that might be there from exhaust scavenging are out weighed by the torque you will produce by just getting boost ASAP.. You want pressure upstream of the turbo, and as little as possible downstream.

I'd be very interested in a technical explanation of why Turbocharged engines need back pressure.

 

The pulse is mostly negated by the turbo. The wheel's blades cause manifold pressure pre turbo... think of it like taking water and pouring it into a funnel. Or sand through an hourglass. It kind of is similar in principle. More water or sand up top causes more pressure to push downstream. So you don't get much pressure once the sand is through the necked part of the hourglass, same thing with a funnel.

I'm sure he is talking about top fuel dragsters and funny cars that have zoomies. But that is like a header with no collector. It still channels the exhaust pulse but it doesn't use the neighboring cylinder's pulse to assist in scavenging like equal length headers would on a car.

You would need to look up a flow chart that looks at exhaust vs intake flow. The turbo does in fact decrease volumetric efficiency of the motor due to exhaust manifold pressure, but they also push air in the intake. Many turbos these days actually are so efficient that they cause less exhaust pressure than they make in intake pressure.

 

the guy i bought it off of claimed it was but the only difference i can tell in it and my 06 cobalt le5 is that the lnf sports 2.5in pipping and a 3in down pipe, now weather or not all lnf's are like that i dont know but my local muffler shop said it was for sure a 3in down pipe and 2.5in exhaust piping