RPM vs gas mileage

[FXDWG]

1996 Legacy GT wagon. Automatic. At 70mph it runs 3,100 RPM +/-
I am only getting 20mpg at best. Engine has recently been tuned up and runs great as far as I can tell. Our 2001 Forester (automatic) is only running about 2,800 RPM @ 70mph. The transmission shifts solidly through the gears.

What should I be looking at?

[evolutionmovement]

A transmission with a taller final drive or top gear or taller tires. Sounds like it's got a pretty short FD. My 1983 GL had that same resultant gear ratio even with 73 HP and my Mazda3 has that as well and it is too damn short. People tend to drive like pussies so I have no idea why car companies seem to think they need to make a surplus of power at cruise instead of getting a few more mpgs. My Legacy runs about 2600 rpm at 70, and still has plenty of power to pass, thanks to the tallest FD of any of the transmissions as well as being a manual.

[Legacy777]

My Impreza is the same way, it's at about 3,100 rpm @ 70. I avg around 21 mpg in town. Longer trips I may get 22-23, but rarely get any better because of the final drive ratio being so "short".

There's not much you're going to be able to do without swapping out the final drive in the trans and rear diff. A lot of work, for marginal returns.

[FXDWG]

How do I find out what gear ratio/final drive this car has? When I compared cars on Kelly Blue Book it showed the same as our 2001 Forester that gets better mileage. My previous Legacy got better mileage. I need to find a Subaru that gets more than 20 on the highway.

[ericem]

It shouldn't really matter if it's at 3100rpm. That is pretty good IMO I would look into a o2 sensor that would affect highway fuel economy quiet a bit. Id also get new spark plugs and run a large gap.

[kimokalihi]

Damn I think my trans puts my car at around 3,500 at 70...at least! I used to know what it was but it's been so long since I've driven it I forgot

[FXDWG]

Just changed the plugs & wires, fuel filter and knock sensor. All my miles are highway and 20 mpg is not what I need for 100 + miles a day travel. My 93 Legacy was getting 28mpg. I'll look into the 02 sensor.

[kimokalihi]

Yeah I think my 90 wagon with a 4EAT from a 94 wagon got 27mpg the last time I filled it up.

[wtdash]

The GT should be 4.44 FD. I believe all the Legacy's w/EJ25 and AT had that from '96-99; 5-speeds were 4.11 (although they had different 5th gear ratios depending on model).

The '01 Forester should also be 4.44, but you'll need to compare tire sizes. Foresters use taller tires vs. the GT's, which would account for the higher RPM's.

Thanks to our friends @ USMB, I found this site: http://opposedforces.com/parts

And this LINK shows the 4.44 under the TRAIN>>Differential(trans)>>Gear set - hypoid listing for the GT.

RE: MPG - I'd say 25-26 @ least @ 70ish. So, something is still not right.