Those with aftermarket exhaust and no valve

geswek · April 13

Those of you who went custom or cat-back with no flapper valve -- do you have this weird kind of "buffeting" sound from the rear on slow speeds 30-40 when shifting to low gear/activating cylinder deactivation? I'm chasing down this weirdness that's been present for a really long time and I think it's exhaust -- it wasn't long before I ripped out the stock and put a Flowmaster 40 on with no valve but I didn't think much of this.

Just curious if others experience this. Hard to explain -- feels like buffeting under the bed. I can make it happens a lot around 20-30-40ish mph when just casually driving and getting the truck into the lowest gear and/or having cylinder deactivation happening along with it.

I was tempted to run it by Chevy to make sure it wasn't like a diff issue or transmission issue. I can't remember if this was present before I put a lift on. I had the exhaust way before I put the lift but didn't really pay attention I suppose.

mafd2 · April 13

Cylinder deactivation will make it sound like a helicopter. Any aftermarket exhaust mod with DFM will sound like crap. Thank goodness my '22 refresh came with DFM delete. I removed the muffler, left the flapper in, screens open and installed a fitted stainless pipe. Sounds great. Not too loud but has a nice sound with no drone in the cab at any speed.

TrueBlue · April 13

Try driving it in L9 so that the DFM doesn't kick in, and see if you still hear it. I have a 14" Magnaflow on mine, no flapper, and it sounds great. I always drive in L9.

The only time I hear buffeting is when I open the back windows, but that's something that happens on most new cars these days for some odd reason.

edit: And I know that buffeting has nothing to do with the engine or exhaust. It has to do with aerodynamics and air flow.

Edited April 14 by TrueBlue

Bikerjon · April 14

8 hours ago, geswek said:

Those of you who went custom or cat-back with no flapper valve -- do you have this weird kind of "buffeting" sound from the rear on slow speeds 30-40 when shifting to low gear/activating cylinder deactivation? I'm chasing down this weirdness that's been present for a really long time and I think it's exhaust -- it wasn't long before I ripped out the stock and put a Flowmaster 40 on with no valve but I didn't think much of this.

Just curious if others experience this. Hard to explain -- feels like buffeting under the bed. I can make it happens a lot around 20-30-40ish mph when just casually driving and getting the truck into the lowest gear and/or having cylinder deactivation happening along with it.

I was tempted to run it by Chevy to make sure it wasn't like a diff issue or transmission issue. I can't remember if this was present before I put a lift on. I had the exhaust way before I put the lift but didn't really pay attention I suppose.

Put a high flow glasspack on mine and cut out the flapper. I only drive it in L9 to keep DFM off. I have no buffeting.