Modifying a Subaru Legacy

I have a 1995 Subaru Legacy that I would like to change the computer chip to give me better milage and/or performance. Any advice on if this is possible and where one would go to buy an aftermarket chip?

I am wondering the same thing. I have a 2000 Subaru Impreza that the mileage sucks. Any suggestions? Has anyone had experience with these with Subaru’s?
Or did you try it Alan_in_Bend?

So, you think that the folks who designed and built your car could have achieved better gas mileage with the car, but they decided not to do so?

Hint: If an aftermarket company promises better gas mileage, I would suggest that you approach their marketing claims with skepticism.

Making sure that your car is properly maintained–including the correct viscosity motor oil–and driving as if there was a raw egg between your foot and the gas pedal will do as much as possible to improve gas mileage. Also, don’t warm up the engine for more than 30 seconds or so, and don’t tailgate.
If you don’t know why tailgating leads to worse gas mileage, post back for an explanation.

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Wow… NO answers in 2007 and another request of exactly the same question in 2020.

I think that is a record.

The correct answer is… NO, a “chip” won’t give you any real HP gain nor mileage improvement.

Thanks for replying. I will look into the suggestions of oil, air filter, etc to help it.
I just bought the car a year ago and went from a Honda civic to the Subaru.
Big difference in mileage. In the city of San Francisco it gets 17mpg.
Which sucks, but the cashier at auto parts store told me his gets the same and it was a gas saving car, can’t remember which. He says because of the hills here and other factors that the gas mileage sucks. He said his car gets 33mpg on the open road.

Alan has not posted since 2007 and if you do a simple web search you will see that your MPG is close to the EPA estimate .

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Your car spends lots of time idling at traffic lights, stop signs and general congestion, and you stop and go again all the time in SF. It is rare that your car spends much time in the higher gears. It’s no surprise that you get poor mileage. Next time get an electric car. Older Nissan Leaf?


I would not want to own a 2000 Subaru. But that’s me.

All true.
All you can do if you want better gas mileage is to…

  • Move to a less-urban, less-hilly area
  • Pay careful attention to its maintenance
  • Pay careful attention to your driving behaviors

Have you not noticed how hilly San Francisco is? Going up those hills half the time is not offset by going down them the other half of the time. Then factor in the other elements of urban driving and 17 MPG sounds about right. If there is a perfect environment for a hybrid vehicle, this may be it.

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Yes it can, but there is a trade off and that is emissions. Especially in California, if you change the chip, or reprogram it, it will NOT pass the state emissions test, even though some of the aftermarket chip makers claim otherwise.

Chips are seldom changed anymore, usually they are reprogrammed, but the reprogramming can be detected and that will automatically fail the emissions test.

Reprogramming can also shorten the life of the engine.

… as we found out from the person who used a performance chip in her nearly-new Ford Diesel pickup, and when the engine self-destructed, Ford rightfully denied her warranty claim.

There is a discussion point here… normally aspirated engines have, at best 3 things that can help performance. Spark advance, variable cam timing (if equipped) and wide-open throttle mixture. Mixture changes can only be used at WOT or the O2 sensors will constantly throw rich mixture codes. Spark timing can be advanced and force the use of premium fuel (as most “chips” or “tunes” do) together with cam timing changes to boost high rpm HP. These last 2 will potentially cause a fail in an emissions test. All 3 together with premium fuel will only help HP a small amount. 5-10%.

Turbo gas and diesel engines are a whole 'nother story as boost limits can also be raised along with the previous 3 calibrations. It can boost power an easy 20 to 30% on many engines with no other changes. Shortens their life, too. Sometimes drastically! Diesels add one more element… diesels can run really rich and make lots of power (as well as Roll Coal) with lots of boost. Until they experience boost run-away and blow up.

The Subie in question has neither a turbo nor variable cam timing so spark and WOT fuel are pretty much all the tools available. With 165 HP, a 5% gain is 8hp. So for that reason, I stand by my “no real HP gain” statement. You might disagree and that’s OK.

That said, my 420 HP, normally aspirated Mustang has a “tune” that is worth about 10% on premium fuel… which is 42 hp… well worth it!


How many miles do you drive if you live in the city? My street rod has a 3-speed auto. I looked into putting in an overdrive. But I don’t drive enough.

Your EPA estimated city gas mileage in the city is 20 with an about oil transmission and 18 with a manual. That assumes your daily drives are the same as their city course. The estimate is also for an Impreza in nearly new condition. Your gas mileage is not so far off that I would do much, other that air in the tires, spark plugs, and engine air filter.

Hello JT Sanders. Thanks for chiming in. I discovered this Subaru forum with the question of what people get in gas mileage.

I’m posting it for those of you that have similar concerns that I have.

I have a rebuilt engine with about 110,000 and a body with 180,000. It’s a 2.2, 2000 Subaru Impreza L wagon. Stick.

I noticed with the Subaru forum that gas mileage is all over the chart and there is talk about winter driving and summer driving for gas mileage.

I’m due to an oil change and will probably put synthetic in it this time. I will check the air filter and understand that different air filters make a difference. The person I bought it from said the air filter was changed, and he did head gasket, and all the stuff when you put a rebuilt engine in a car. Saw in the subaru forum that a complete brake job made a difference as well as some reporting better gas mileage with higher octane gas.

What are you folks with Subaru’s getting in gas mileage? I will probably post this question separately.

You will not gain anything by synthetic oil except possibly longer time between oil changes . An air filter is pretty much the same across the board and a Google search will tell you that the modern engines are not effected by the air filter as the old carb engines. Just relax and drive sensibly because where you are you are not going to get much better then you do know.


Unless it’s badly clogged, an air filter will not significantly change fuel efficiency in a modern fuel injected engine.


It appears that your mileage is about as expected. For your next car, consider looking at for EPA estimates for city driving. The estimates are for comparison between cars you might want. You may not equal their estimates, but the difference will be mirrored for any car you buy. Enjoy your Subie for now.

No surprise getting poor mpgs in San Francisco. I remember a rental car that could barely get up the hills with full throttle.

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