I was thinking of a way to save on gas....i'm going to drive to cali from wisconsin. I have a JDM Ej20G and will leave on spring break to go. what could I do to save on fuel as far as tuning? I'm thinking of getting something to control AF and a boost controller and turning boost down "lower" than stock and leaning it a little bit because of lower boost? how much power would expected to be lost? is there any real gain from doing this? what else can I do? :confused:

any thoughts or input is great. call me stupid or whatever lol just an idea..

well if you are planning to have more boost than 0 psi, you can forget about fuel economy. My goal while trying to make fuel economy is to keep boost about -6 psi and keep the car @70-72 mph. When i drive like this, i can go around 300 - 320 miles with a full tank.

in what car? I have an impreza L with the 13Gal. tank and swapp... MPG numbers would be better.

With my WRX when it was Stage 3. Now it's stage 4 and i can go about 250 miles with a full tank.

When you are cruising you aren't in boost anyway to turning the boost down won't help anything. Opeing the exhuast up as much as possible helps a bit with fuel economy.

<-- used to get 29+ mpg on the freeway @ 80mph with a TXS stage 4 setup.

waow that sounds good

Just stay out of boost. I've thought about the whole mpg thing way too much.

Here is the nutshell version: The compression ratio of the engine is going to limit how much mileage you can get off boost.

I don't know what engine management you are using, but chances are you are at the stoichiometric ratio of air:fuel--AFR of 14.7:1--while cruising most of the time. It ain't getting any better than that unless you squeeze more pressure out of each combustion event, and that ain't happening unless you up the compression ratio.

You have two other options to improve fuel economy: 1) shed weight (it's not a bad idea for performance either) 2) reduce frictional losses (here you have aerodynamics, thinner lubricates that permit easier movement in the engine and transmission, and lower mass powertrain components--that lower inertia losses).

A couple year's back Saab created a "variable compression ratio" engine. It had a cylinder head that cracked open on one side, with a flexible bellow. That allowed the engineers to raise the CR when cruising for best economy, but lower the CR when the turbo kicked in. Simply amazing engineering, brilliant really.

Quick MPG Tip: if you can change out of "auto" mode for AWD and put the power to the rears you'll pick up a good 15-20% more mpg. Frictional loss? Who knows.

I get about 25-26mpg in my Stage 4 WRX when cruising and avoiding boost as best as possible.. I used to get 27-28 but then I swapped trans and have a much lower gearing now.

Everyone's advice is spot on. Not much to be gained by tuning, but lots to be gained by changing driving habits.

Stay out of boost, and coast in gear down long hills. Don't put it into neutral, which uses more gas than coasting. If you know that you'll have to climb a hill shortly after a down hill, keep light throttle to build up speed so that you'll need less throttle to make it up the hill.

Finally, drive as slow as possible. I drove 350 miles following a truck when helping my mother-in-law move at speeds of 55-60, and got 32mpg, even with the drive including some small 2-lane roads and mountains. Driving 75-80, my mileage drops to 27mpg.

Yeah, drag behind trucks for aerodynamics, the trucker will want to kill you, but you'll pick up many mpg.