Question exhaust - Toyota Tundra Forums : Tundra Solutions Forum

jets · #1 (**permalink**) 03-20-2009, 12:25 AM

About a week ago, I decided to cut the piping from the muffler back off because it was hitting the axle when I bottomed out. Since then my MPG has gone down the drain. it was bad before hand, but now im getting 7-8 mpg when I got around 12 before that. I have 3 inch piping from cat to 3 inch flowmaster then its an open exit. My question is, what is the best size muffler and muffler to get better MPG because I am suffering big time!

Not only that, the flowmaster has an annoying drone and Its hard to hold a normal conversation in the cab with it. im thinking of going to a magnaflow and dumping it. Do magnaflows drone at all? sorry for the stupid questions, just trying to vent my frustration on this issue

Negra · #2 (**permalink**) 03-20-2009, 08:33 AM

Get a muffler with a more reasonable flow ID,3" is obviously to much.
Best I can figure by your Sig is that you have the truck lifted and rolling tall rubber,No ?

I cant understand why you would drop 3-4 mpg by removing only the tail-pipe section ?
Unless you dropped the tail-pipe section and lifted the truck and added taller tires all in the same stroke ?

Hard to speculate with limited information

Regardless,the 3" exhaust is still going to be the primary suspect.

jets · #3 (**permalink**) 03-20-2009, 11:05 AM

I am also assuming it is the 3" piping as well. what piping should I drop down to? I know my lift, tires and skid plate play a major role in my mileage but i was getting around 12 just before the cutoff and was satisfied with that. should 2.5 single in and out work better?

Negra · #4 (**permalink**) 03-20-2009, 01:54 PM

What motor do you have ?
Stock manifolds ?
High mileage ?
Any CEL's ?

jets · #5 (**permalink**) 03-20-2009, 03:32 PM

i have 62K miles on my truck with the 4.7 and no CEL's. But I do know that my stock manifolds have a slight leak in them because I can hear it. It could be that something besides my exhaust is the problem and just ironic that it happened at the same time I cut my exhaust?

scottnmos · #6 (**permalink**) 03-20-2009, 06:21 PM

I have a 3" outlet on my magnaflow and have had an increase in mileage......I have the 5.7 though...

Negra · #7 (**permalink**) 03-20-2009, 06:41 PM

If you have a manifold leak and have had it for some time there is a chance it has effected your 02 Sensor. Improper readings from the 02(which should throw a CEL but doesn't always) cant cook your cats.
If your cat's are fried it will effect engine performance,cooked cats also don't/will not throw CELS in many instances.

I dont suppose you have any Warranty ?

jets · #8 (**permalink**) 03-21-2009, 12:43 AM

well I think I may have solved the problem. I took off my intake and put the stock box on and can already tell my mileage has been improving! I drove almost 40 miles today on a quater tank and before i drove 20 on that! I am so stoked to have my mileage back. Thanks for all the help but I think I am going to have to get my manifolds replaced or fixed soon. But would going to a 2.5 inch piping yeild me even better mileage? or 2.25 inch piping?

AGR1755 · #9 (**permalink**) 03-21-2009, 12:53 PM

well I think the stock piping is right in between 2.25 and 2.5...2.5 is probably your best bet...and if you are going to have to replace your manifolds then you should just consider a set of headers...but 2.5 piping is much better for performance on our trucks other than stock