I purchased my FD around 6 months ago. When I got it, it was all stock + catback with 5k on the new PFS-installed motor. The best combined MPG I ever got was 17. Since then I have done a few reliability mods (koyo rad, pillow *****, downpipe, etc.), added an ebay upgraded smic and a custom twin-k&n intake. This weekend, the first time I've really driven it since the IC/intake upgrades, I clocked nearly 23 mpg combined highway with agressive mountain driving.

On one hand it's great to get decent gas mileage but on the other I'm worried that maybe my car is running too lean now? Boost pattern is fine, never overboosts past 10, runs like a champ, making stock power. Is this a resonable increase to see with these mods or is something wrong? On my other car I've increased my mileage over the EPA factory specs by 7 mpg highway through intake/exhaust mods and this is on a stock motor with 183k miles on it, so I know it's do-able.

 

I think it is suposed to be a good thing right?
But either way if you want to know if you are running lean or rich.. there are two methods.
1. Check your spark plugs... if the tips are white... then your running lean. If they are black then you are running rich.
2. Get a wideband and you will know real time!~~

 

I changed my plugs post arrival to california by a couple tanks of gas. my plugs have never been this white and Ive romped on it way harder previously. Damn 91 octane.

 

I highly doubt that is the stock engine.

 

I've seen highway driving in the low 20's on my car, even when coming home from first buying it with just a downpipe/catback for mods. Around town right now, I typically get about 17mpg, but I drive pretty conservatively most of the time.

Stock EPA numbers are 17 city, 25 highway for a manual - that's straight out of the dealer brochure (just checked ).

Dale

 

Alot of people notice "big" swings in MPG depending on the ambient Temp. It was probably alot colder 6 months ago then it was now.

Cruising at 65mph rather than 70mph is usually worth around 10% better mpg depending on the car. How accurate was your testing to determine MPG?

Bottom Line: Your mods probably helped, but not that much.

 

I get around 21 to 22 combined mileage with some full throttle runs

 

Check your math you will not get 23 MPG with spirited driving unless it was down hill only or just a few charges. Also your mods will not help to any significant degree. To improve mileage to the degree your talking would require major tuning or internal modification perhaps both.

I average 11mpg city now (stock 15-16) and 23-26 @ 75 stockwith the cruise and AC. If you calculate the consumption at the pump I'm pretty sure you find that it's lower or you have a very light foot.

Also keep in mind that the EPA figure is reduced by about 10% to reflect real world driving conditions.