Just got a new 40 series on my 03' F-150.

Wen't from 14mpg to 11mpg. I know at first i wanted to hear the new loud cool sound, but now 3-4 tanks later, i dont see a difference other then less mpg. I keep her below 2000rpm's, any thoughts?

 

Too much pedal?

I think people around here call them "Slow-masters."

 

Strange, i didnt lose or gain mpg with my flowmaster. give the muffler a while to break in, maybe that'll do the trick.

How does she sound?

 

usually you get less MPG, because your foot hits the right pedal harder when you get a new exhaust.

 

But the sound is soo addicting...

 

oh trust me I know lol, but that does lead to less MPG. My muffler delete on my 5.4 made mine go bye bye FAST!

 

flowmaster = less torque-put a free flowing straight through muffler on and i bet your mileage goes back up

 

Nope they are called Flow-Stoppers. On a dyno they have shown a few times to kill hp. (Ive only seen it on Mustangs)

 

It all depends on how big a pipe and muffler you run. You need to have backpressure on your exhaust. A lot of people go and put 3" exhaust pipe and muffler on their stock vehicles and wonder why they are losing power. I have a 92 Mustang thats my race car (best of 5.88 1/8th mile) and I have 3" exhaust on it. That motor is highly built to. I put 2 1/2" SIDO Flowmaster 40 series on my truck and picked up signifigant amount of low end torque.

Just my $.02

 

I will take the little loss in HP for the sound. Nothing sounds better than a flowmaster, especially on a big-block. The little horsepower you lose, you will never even feel...(1-10hp loss, if that.... is nothin', unless you are a drag racer trying to compete or something)

 

I concur about the sound......I have never lost power switching to a flowmaster. If they made exhaust products that took power away why have they been in business so long? I am not saying other mufflers wont out perform it but it does add power.

 

yea man i lost mpg on my 4.6 i put a super 40 and i started with 18 and now i get 14 mpgs

 

I'm kinda in between on this.....I see all the negative posts about Flowmaster yet there are plenty of fast vehicles running them. My truck had a single 3" Flowmaster 3-chamber cat-back when I bought it, next time I dyno I may drop the muffler for a run just to see if its costing me anything....

 

I get asked all the time about my Flowmasters... People wanna know if I get better Hp, or increased MPG. My response is always the same: "Hell if I know, but they sound cool."

Had them on a 98 Tahoe, My 00 F150, and now my 07 KR Screw. The day I bought the King Ranch, was the day I put on my pipes. I believe my truck had less than 30 miles before the stock muffler got cut off.

The shop I get them done at, does all the welding and bending of the pipe. I have put about 265,000 on two sets of Flowmasters. I have NEVER noticed decreased gas mileage. Do they cut horsepower? "Hell if I know, but they sound cool."

 

just like 04s&bfx4 said, its not necessarily that the flow makes the mpg go down along with the hp, its all about the back pressure. i have 4 cats on my truck which makes a good bit of pressure and i have a flow and i actually gained mpg and i really couldnt notice any hp differnce. but one thing i noticed is when i turned up the music instead of listening to my pipes, i saved gas.