A little bit of history here. I am on my third Lariat. The last one I had nine years and traded the old guy in at 266,928 miles. I had a Flowmaster 40 Series muffler with duals out on the past two trucks.

I now have a 2007 5.4 Lariat and have changed out the bus sized muffler to the Flowmaster 40 Series and duals out the back.

Neither of my earlier trucks had the fuel efficiency guage that the 2007 has. What I noticed is an immediate reduction in fuel efficiency. I was at 19.7 mpg avergae on town with the factory muffler. I am 19.4 mpg and cannot get it to budge higher than that.

Is this normal??? Is it because of the reduction in the back pressure??? I guess my next question is am I doing any damage to the motor???

Appreciate any thoughts.

DaWG

 

Not unexpected given the baffled design.

Check these out:

https://www.f150online.com/forums/4339424-post22.html

https://www.f150online.com/forums/ex...ust-guide.html

There are more efficient options ...

BTW - as detailed in that *excellent* new sticky by Mr. P (Emperor Junior), backpressure is not relevant - it's the reduction in scavenging that is the issue. The 'bus-sized' muffler, being of huge internal volume does at least not incur as much of a penalty in this regard - a reasonably designed OEM compromise of efficiency, low noise, no drone, and cost. And it's stainless to boot. The mufflers on the newer 09+'s are even better.

MGD