Jump to content

How Important is the Backpressure Valve?

noJeepshere

By noJeepshere
in Engines & Drivetrain

Recommended Posts

noJeepshere Enthusiast

noJeepshere

Posted
Posted

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 Enthusiast

1300c

Posted
Posted

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 Enthusiast

Krusty

Posted
Posted

............ 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.......... :dunno:

 

 

 

post-168136-0-95592900-1497531302_thumb.jpg

 

post-168136-0-36278200-1497531322_thumb.jpg

post-168136-0-95592900-1497531302_thumb.jpg

post-168136-0-36278200-1497531322_thumb.jpg

post-168136-0-95592900-1497531302_thumb.jpg

post-168136-0-36278200-1497531322_thumb.jpg

post-168136-0-95592900-1497531302_thumb.jpg

post-168136-0-36278200-1497531322_thumb.jpg

noJeepshere Enthusiast

noJeepshere

Posted
  • Author
Posted

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.

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Latest Articles

  • Posts

    • GMCustomerService
      Damaged Left Rear Bumper & Left Rear Quarter Panel - Repair Questions

      By GMCustomerService · Posted

      Having bumper and other body damages can be very frustrating, especially as a result of a parking lot collision/bump. Our team wants to learn more about the damages to your truck so we can look into ways we might be able to help. When you get the chance, please fill out our support form with more details: https://s.gmc.com/support-request . A member of our team will follow up with you as soon as next available. We want to get you enjoying your truck to the fullest again. 
    • PhilB
      Gas Prices

      By PhilB · Posted

      Did you even read this article?   Even the title of the article says "U.S.-Iran Deal Doesn’t Mean a Swift Return of Oil and Gas Flows"   Remember, crude oil prices are based on FUTURE purchases by the oil companies.  Gas prices are based on FUTURE purchases by the station.  This article stated that many of the oil producing nations have to restart their processes to get the oil produced.  Then the oil has to be shipped to wherever.  And it doesn't get there overnight.  And most of that oil is not coming here. Check out this site:  https://afdc.energy.gov/data/10621   A graph will pop up to show where the US imports their oil from.  Notice that there isn't a lot of import from OPEC and Iraq.  Most of the US import comes from Canada. The US oil produces are selling their oil on the open market, which is why the US fuel costs went up.  So you're correct, the US oil companies are going to slow walk the price downward.
    • GMCustomerService
      Tranmission stays in Low

      By GMCustomerService · Posted

      Having codes and an engine light with no hints on what might be causing it is nothing short of frustrating. How long have these concerns been present? We want to know more so we can look into ways we might be able to help you. When you get the chance, please fill out our support form with additional details on your experience so far. A member of our team will follow up with you as soon as next available: https://s.gmc.com/support-request 
    • GMCustomerService
      Defective Brake Pad Wear Sensor?

      By GMCustomerService · Posted

      Knowing the life of your brakes is a highly important status to keep track of. If you suspect your brake sensors need attention, please fill out our support form with additional details on your experience. When did you last take it in for inspection? Our team will follow up with next steps as soon as next available. Please include your username and GM Trucks Forum in the form as well. Support Form: https://s.chevy.com/support-request 
    • teamjnz
      Stabilitrak conversion to Z71

      By teamjnz · Posted

      I just purchased a 2004 Tahoe with 148,******. I used to have a 2006 Suburban that had the push button Auto 4X, 2Hi, 4Hi and 4Lo. When checking out this truck I noticed it had push button but didn’t focus on it. After the purchase when driving home, this is when I noticed it was different and after a little research found out it has the AWD stabilitrak system. I don’t live in an area that requires AWD. I bought the truck to start a new adventure in life with off roading, now that the kids are all grown up. I purchased the truck knowing it didn’t have the G80 rearend but plan on re-gearing to drive on 33s or 35s and upgrade with a rear locker and still be able to tow when needed. Blah Blah Blah Anyway I know am thinking about converting the stabilitrak  to Z71. I know I will have to replace the transfer case. So now the information gathering stage is happening to see if it is worth it. Is the front AWD stabilitrak differential different when compared to a non-AWD front diff? Will I need a completely different front differential or can it be converted? What else should I be considering? I did see something in a video for GMT900 platform with removing the ABS fuse that disables the stabilitrak and turns the truck into a 2 wheel drive. Would that work in the GMT800 platform?

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...