Car is a 2005 G35 automatic with K&N filter, Z tube, 5/16 inch MotorDyne Plenum spacer, and MotorDyne A R T pipes. It was tuned by Osiris when it had all this and a full fast intentions exhaust. When driving 100% highway, my best was 26.7mpg.

I have removed the the exhaust and replaced it with the stock system, and it seems like the gas mileage is really bad. I have mostly been driving local and get about 10mpg.

So the question is, do you guys think I need a retune? Would I be getting better gas mileage if I replace the MD test pipes with stock and then getting a retune?

 

Def get a retune. Replacing with stock cats won't help you, they are more restrictive then art pipes.

 

yes, def retune. I had a manual, mostly city driving and I was getting 15mpg. leave off stock cats.

 

bump。。。

 

This is my reasoning as well, anyone else have input on this?

 

Just curious... why did you go back to your a stock exhaust setup?

 

What mods do you have?

Didnt like the sound of aftermarket. Seems like all aftermarket exhausts removes the "jet" sound. Would be nice if there was an exhaust that only enhances it.

 

Agreed. Same reason I took mine off.

 

bump for more opinions

 

fi?

 

I don't think fi would help with gas mileage lol.

So I did some calculating today and got 9.3mpg with 100% city driving and 19.3mpg with 20% city, but slight traffic on the highway coming home.

9.3mpg was calculated with a trip of 113 miles
19.3mpg calculated with trip of 70 miles