It's pretty normal for your mileage to go down with bigger injectors fuel pump and cams if ur boosting more and making more power. The whole reason u upgrade ur fuel system is because u need more fuel so common sense would say ur gonna use more, but also sounds a bit drastic especially on pump gas. I would check all your vacuum lines and inter cooler lines like was said. Your car definitely doesn't sound like it's running very good which could hurt mileage....

I used to get about 16-18 mpg fairly spirited driving on 93 pump gas and I was making about 360hp/350tq now on e85 only difference being pte 1200cc injectors with tad more boost making 405hp/397tq I havent calculated it accurately, but my mileage aint very good lol....... like wizzo 8 said if u wanna play u gotta pay.

Good gas mileage and power are like oil and vinegar the don't go together.

 

the shop I took it to boost leak tested the car for me. Shouldn't have any issues in the department.

Mods to the car are Intake, TBE, MBC, Wallbro 255, GSC s2 Cams, Supertech dual valve springs, And I believe my tuner had 1200cc injectors put in. Clutch is a Exedy Twin disc.

Even if I stay out of boost 100%, I still get the same results. Another reason why I thought it could be from the friction of the clutch and flywheel.

 

I got 16 mpg on 780 and e9 turbo with m2 cams

 

your doing good i get abuot 12-14 MPG!! but in my cars defense, I drive it like i stole it and the winter fuel blend in ILL is ****, hense why fuel prices drop in winter here as to summer fuel prices. Some type of blended fuel they use in ILL here in winter it just sucks same for diesel.

 

Did you ever figure out why your getting bad gas mileage? Since winter came I'm getting horrible gas mileage!!!! Like 150 a tank.

Any help please!!!!

 

i'm not driving an evo 8 or 9 but i have an x with s2 cams... and with that being said BEFORE a tune.. i have been getting, 9-15 mpg around town... I will be getting tuned this weekend.. so we shall see my mods are. im pretty sure the crappy gas milage is to the tune though

here are my mods :
Id 1000 injectors
OBX fuel rail
AEM fuel pressure regulator
Grimm speed 3 port
ETS 4’’ inch intercooler
ETS upper intercooler pipe
ETS lower intercooler pipe
ETS intake
AMS downpipe
Full 3” custom exhaust
Deatchwerks 65c fuel pumps
Cobb access port
Stock turbo
Stock head
Stock block
Stock ECU

 

It's normal for mileage to get a bit worse during winter since you're spending more time letting the car warm up before driving, etc. Shouldn't be that bad though, I'm at the ¼ mark and about 225 miles on this tank so far.

 

Op try running some Lucas fuel stabilizer should help mpgs.....if it don't improve I would look into a vacuum leak or boost leak as mentioned earlier n checking for it....around town I'm gettin close to 200 a tank....more so if its mostly highway......I'm on s2 cams, was on hks 272s before and my mpgs didn't decrease even after adding an intake mani and tb as well. It's either tune or injector scaling, any cels?? Best bet is to have your car datalogged, a lazy 02 sensor or bad maf can also cause bad gas mileage in addition to worn out plugs.....good luck.

 

Honestly it could be a host of things, so if you have the money and a good tuner who knows their stuff, take your car to them, you will pay up front but it will save you money in the long run. I just got tuned on a DBB FP Red with S2's and I was honestly shocked at my gas mileage as I drove like 2 1/2 hours home after the tune with 2 hrs of those miles highway and I was only at a little pass quarter tank..........so all in all if you have the tuner and the money, pay so u can sleep better at nights, if not, then best of luck to you fixing this issue.