How Important is the Backpressure Valve?

[noJeepshere]

I put in a Magnaflow cat-back exhaust system, single 3" pipe from the band clamp behind the third cat out the factory spot with an 18" muffler and the backpressure valve. I was driving it around with the windows down and noticed the sound coming out the tailpipe sounded like shit. Windows up it sounds great, but with them down it sounds like there is a pinched pipe. Really does sound terrible. I took some bailing wire and tied the backpressure valve in the up position and the terrible noise went away, but the smaller diameter muffler resonated terribly. I'm thinking of putting in a wider muffler (one with more baffling) and removing the backpressure valve. Like the title says, how important is that? I noticed a lot of other systems don't utilize it so I think it can't be that needed, but I didn't design the truck.

[1300c]

The exhaust valve is there to stop the thumping helicopter sound from entering the cab when your truck is in v4 mode. Depending on how sensitive you are to the thumping sound you could wire it open. I have the muffler delete with the flapper left in so I know the exact sound you are describing. I hated it until I had my wife drive the truck with me outside it, and it sounded great, and completely different than inside the cab. I did notice when I had my windows down, and my rear sliding glass open it sounded more like it did when I was outside the vehicle. So I guess that flapper sound just carries inside the cab more. Windows up though mine sounds awesome too. Hope this helps.

[Krusty]

............ I'm thinking of putting in a wider muffler (one with more baffling) and removing the backpressure valve. ...........

 

 

I have just that and very happy with it......... See thread linked in my sig (thread covers the 5.3L too)........... FYI - It's called the flapper around these parts..........

 

 

 

 

[noJeepshere]

If it's just there to stop the thumping, then away it goes. The only time I had issue with the thumping while the flapper was wired up out of the way was at lower speeds, on the interstate doing 2000 rpm I couldn't tell the difference between V4 and V8 modes, but it resonated worse than a flowmaster 40 series. So flapper down it is until I get the bigger muffler. I like Magnaflow because they have a sweet sound but don't drone typically.