would running no muffler right after the cat cause a loss in MPG. if so please explain why :P i heard about backpressure affecting it but idk much about that.

 

back presser leaves a lil big of the unburt gas in the motor. and the 2nd time around it burns most time. well that is what i was told any ways.
this came out the moth of a guy that was about 60 years old and had be racing sense is was 19 and has taken more 1fistes then i will

 

what does that mean? backpressure is bad?

 

I have n over head console an when I ran no muffler my mileage went up from 18mpg highway to 23 highway but was super loud an annoying. I'm gunna hollow my cat run straight pipe through it an weld it up so it looks stock them my flowmaster an run my exhaust out the lower section of rr quater panel. Just for somethin different.

 

mufflers dont really affect back pressure they just move the exhaust around to muffle it and change the tone...but the concept is that you need a certain amount of backpressure in the system to much loss in backpressure leads to loss in horses too...so if your straight pipes all the way back you prolly will see a lower mpg cause theres no back pressure (thats why there isn't 3" exhaust kits available for a lot of vehicles its to much open pipe)

 

As macgyver says, the muffler should not affect the back pressure unless clogged.
But MPG is affected by many things. Have a look in through the archives with the
subject heading of MPG or bad mileage and you will come up with dozens if not hundreds of posts with similar themes. This combination of I6 engine and and XJ chasis has resulted with thousands of reports of bad mileage and bad cooling UNLESS everything is in perfect running condition. Which of course means replacing more parts than you intended.

 

^^Well put^^

 

no running no muffler shouldn't do anything bad to your gas mileage. your back pressure shouldn't be affected negatively either. the only time you that the back pressure would hurt the car is open header. but thats illegal some other things like lift size, tire size etc. would be a bigger factor in your MPG.