Exhaust Help

[BubHimself]

I just put in a K&N Gen II intake system and a Corsa Dual Rear exhaust on my 04 silverado. I was expecting to gain some gas mileage but it turns out i've lost about 40 miles to a tank. Someone please tell me what is going on? The dude at the local tire pros says its prolly because i went from a single to a dual exhaust. is this right? oh yeah, it isn't because my foot has gotten heavier, i am driving at the same speeds as before.

[BurbanZ71]

I have heard the 5.3 engines need some backpressure to run well.

 

So, if you went from the stock exhaust size to much bigger combined you will lower the backpressure which means less low end torque. This in turn will drop your MPG.

 

On my Suburban w/ a 5.3 I have been told duals should be no more than 2" for this backpressure stuff.

 

Do what do you have for Engine / tranny / gears ?

[Deere_Daze]

The K&N and exhaust allows the engine to flow a lot better than stock, so the computer is feeding the engine more fuel to compensate for the leaner air/fuel mixture.

[mudbug660]

The way I see it is that Gm has engineered the exhaust to give you the best mpg at highway speeds while keeping the noise down. So when you switch to a dual exhaust setup that changes the diameter of the pipe. I'm thinking the stock size is is a single 3" pipe (I could be wrong) but the area is 7.07in^2 and if you dual it out and the pipes go from 3" single to dual 2.5" then the area after the muffler is 9.8in^2. Because the area goes up it slows down the velocity of the exhaust air. Now this is just my opinion but I think when you change the velocity it's hurting your power down low. If gm though that a bigger exhaust pipe was needed to get better gas milage, they would have done this from the factory. At higher rpms the velocity is back where it was at before the dual exhaust was installed so you get the performance increase. After thinking about this for a while I think I'm going to get rid of my flowmaster and duals and just get a single 3" exhaust with another muffler of my choice. Now this is just speculation I could be wrong 100%. Just my opinion

[BubHimself]

...okay, yeah that makes sense, the tips are 4" but they are pretty shallow tips and the tail pipes to them are a lot skinnier....so i should look for a single exit performance exhaust with smaller tips...anyone got reccomendations?

[ken1mod]

Gentlemen,

 

Darn it. The thing is engineered to give best performance. Anytime you mess (and that is the operative word) with it you will lose something. I find low end torque is the first to go. Don't mess with the systems unless you know what you are doing. The fat guy on the K&N commercials is only worrying about his own wallet.

 

Ken