Clamping the flapper valve effect fuel economy?

[jw1595]

What's the consensus on this It definitely sounds better but is there any evidence it affects your fuel economy in a negative way? 

[f8l vnm]

Highly unlikely it does anything to the MPG. Only thing that effects the MPG is your right foot 

[econometrics]

Yeah, I had my 5.3L clamped open for a little over a year before I took the plunge and got a catback exhaust. I couldn’t tell a difference in MPG at all from the first 6 months without it being clamped. 

[fatwhiteboy]

The flappers are quite restrictive even when open.  Other companies use these as well, some are spring and some are electric.  All they are designed to do is to stop drone during cylinder deactivation.  I put the Borla Touring on my Truck and it sounds great, absolutely no drone at any speed.  If they designed the exhaust properly they would not need this things.   If you notice in your extended warrantee exhaust is one of the exempt parts that are covered.  They must have a pretty high failure rate of these getting stuck closed.