Attn: TurnWRX

I think shifting at 2K might be aggravating fuel economy issues, using more fuel than if the shift point was 3.5-4K. Once you shift at 2K, the rpm drop into the next gear probably is putting an excessive load on the motor, plus is decreasing the inertia of the car itself. You may be falling into an rpm range that is disagreeable with a short-stroke 2.0 liter low compression motor (when not boosting), like if you were to ride a 10-speed bike, and try to hop on and immediately click it into high gear (largest pedal sprocket, smallest hub sprocket), and try to gain momentum......you know what a ***** that is on your legs and your lungs, it is much easier to start in a lower sprocket until your legs are whizzing and feeling no resistance, then you shift up.....your motor and your car is the same. If you constantly "short-shift" the car, you are laboring the motor (main and rod bearings take a BEATING driving like this, especially when the motor oil is cold!!), and you will find you are using a wider throttle angle than if you were to shift at 3.5-4K (I have no idea how the Subaru ECU works, but I am pretty sure the ECU bases injector duration on throttle angle [via a throttle switch....like a rheostat?], and air flow and manifold pressure), I bet the ECU sends a fat mixture when it senses a wide throttle angle and low manifold vacuum, (short shifting will cause this situation), I'm sure there are a ton of people that can explain the ECU's mind better than me, because I am very new to these cars, but I hvae experience tuning HP engines, dynoing and reading BSF charts (fuel volume vs. rpm vs. power curve). Try moving your shift points up 1500rpm and be light on the throttle and you will see an improvement.

 

Try running 800cc injectors and see what kind of mileage you get. It ain't pretty let me tell ya.

ben

 

if i hit 175 i'll be happy because the bottom half of the needle goes by a LOT faster than the top half :-/ but usually i'm around 145-155 and hit from 280-315 per tank. keep in mind this is about 1/3 street and 2/3 freeway

-dRu

 

why don't you just try shifting at the subaru recommended shift points? shift the 2nd gear at 15mph, to 3rd at 25mph, to 4th at 40 mph, and 5th at 45mph. watch your boost gauge when accelerating and try not to let the gauage read over 0 (keep it in negative vacuum).

 

halfway marker about 160, full tank about 260 with the empty gas light on with the pin on E (still got about 1.5 to 2 gallon left in the tank). i was just curious. don't suggest trying that, not good for your car.

that is city and freeway driving.

eric.

 

Shifting at the recommended points is ok, but 5th at 45 is stupid, 5th is so damn tall you're not going to gain any ground.

 

well i just hit 213 for the halfway mark driving all highway, and few miles driving very spiritedly (sp?) with fellow subies, and two evo's.
lately ive been getting better mileage. driving under 3k, and at a very consistant speed really works.

 

yea i noticed how the needle isn't exactly correct. if you notice, u can get close to 100 miles on the first 1/4 of the tank, then the 2nd quarter of the tank i get 50? ....then the 3rd quarter i get about 50, then the last quarter i can get 75~100 before the light turns on. and aren't the light supposed to come on when u have close to 1 gallon of gas left? because i have travelled for another 30 minutes on freeway going constant of 65mph, after the light came on, then i finally took my gf back to her city, and we went to fill up. and the gas stopped at 14 gallons. meaning i still have 2 gallons in the tank.

 

Your guage may be a little off. Instead fill the tank, "0" out the trip odometer, run it down to about 1/4 then refill the tank. Take the mileage and divide it by the gallons you just put in and this will give you your MPG. For example: this is from my RS, 309.6 miles on the trip odo divided by the 11.318 gallons I put in equals 27.35 MPG.

 

Fuel guages aren't very precise. They use some sort of floating ball/device in the tank to measure how much gas you have in the tank. Kinda like the device in the toilet. When you fill up your gas tank to full, the ball device is actually submerged (hence the reason the needle stays at full longer than any other point). One you've used up a gallon or so, the ball is still floating at the top, but not submerged anymore.
One of the reasons why it's not very accurate, but it's conservative enough to let you know that even when the needle points to Empty, you still have 1-3 gallons left in the tank.


Btw, I got this from howstuffworks.com

 

i do this exactly, and i didn't know it was suby recomended, i just naturally shift at those points


a buddy of mine has a mini cooper type-s and he NEVER lets it rev below 5.3 grand. im like, wtf are you doin
he'll be going down the street doin 40, in 1st gear, im like your crazy
and he swears its "supposed to be driven that way"
ima laugh when he has issues

 

Shifting at 2Krpm is way too early.
This is the problem.
You realize you never hit full boost driving like that?
The shift points in the manual are super conservative, assuming flat ground, even acceleration and good shifting.
Definitely not SF driving.

The gas gauge line at halfway isn't really halfway which is another problem.
Using the gauge to judge mileage is silly.
Reading the car manual is good.

The Empty light comes on when there is anywhere from 2.3 to 4 gallons left.
The manual states that it comes on with 2.3 left but doesn't go off until filled to 4 gallons, however, this is a bit misleading.
If you are at 3 gallons, and take a long hard turn or accelerate and swerve, the fuel sloshes, the empty light gets activated, the fuel settles, and the empty light stays on since it is below 4 gallons.
So the fuel warning light can be quite misleading.
You should always have at least 2 gallons left when it comes on, and if you know your mileage, you know how far you can go (assuming you have no water in your tank).

Do as suggested and use your trip meter to track from fill up to fill up, divide the miles on the trip by the gallons to fill up.
Write it down.
Reset the trip meter and do it next fillup.

I get 24mpg highway, 18-20 city.
I drive in fourth gear a lot of the time shifting at 4.5K rpm when not accelerating fast.
Peek power on the stock motor is around 5.5K rpm, so shift above that if driving hard, otherwise a bit lower.
There is nothing wrong with being in 4th at 5K rpm and coasting down to like 2K and cruising, until you step on the gas hard, then its FUEL FUEL no torque lug lug until boost hits - you are wasting gas.
Better to downshift then accelerate.

The howstuffworks info is correct, the fuel level sensor in our cars is an arm with a float on the end.
Not only does it submerge when the tank is full, it can bump the side of the tank too, and it swings around while driving.
So the sensor reads slow to allow for this.
Quite funny to be driving in the mountains with a full tank, then a half empty one, then a full one, then 1/3.