finally 40MPG cruising on the highway (impreza 2.5L 4WD)

[ever_green]

i think 31mpg was my highest mileage on a tank because i do almost all city driving. but 40mpg on the highway is possible after a bit of tuning (keep in mind this car is rated 20c/26hwy EPA) :

http://www.youtube.com/watch?v=b2_yar4Cnt8

video notes:

• engine was at 2600rpm
• a/f was at about 17:1
• ignition timing was incorrect, the log on my laptop indicated 44-48
• cruise speed was set to 66mph
• BHP or horsepower display is too high by about 15-20%

what i did to gain 14mpg improvement crusing:
engine and drivetrain mods are in the signature. but the only economy mod i have is an ECU reflash specifically for fuel economy purposes. This included leaned out A/F mixture from 14.5:1 to 17:1 specifically @2500rpm in closed loop, and general leaning across the powerband. drivebywire throttle map modified for fuel economy. i-avls engagement was modified using a circuit built by a NASIOC member, thanks a lot buddy. Ignition timing was modified by a tuner, i'm not aware of the details for that.

I'm sure pulse and gliding can give me +45 MPG highway figures. just need to find an excuse to get on the highway now, since everywhere i need to go is city travel.

[serialk11r]

That's an EJ25 engine right? Nice! I wish I could tune my engine to run lean like that as the engine load level is just way too low for efficiency on the highway, but air fuel controllers cost too much.

What did you do to the AVLS? As I understand you have a SOHC motor so you can't have the high lift lob engage and mess with the phasing.

[ever_green]

Originally Posted by serialk11r

That's an EJ25 engine right? Nice! I wish I could tune my engine to run lean like that as the engine load level is just way too low for efficiency on the highway, but air fuel controllers cost too much.

What did you do to the AVLS? As I understand you have a SOHC motor so you can't have the high lift lob engage and mess with the phasing.

i'm not a tuning expert so im not sure, however you can read a thread about it here on nasioc:
Is it worth modifying the AVLS in our cars via engine management or hardware? - NASIOC

this thread is mostly discussing possible power gains and not economical gains. but i think my tuner just did the opposite. he basically built a circuit to prevent ecu from engaging high cam profile between 1500-2500rpm. so i'm operating in low lift below 2500rpm and high lift above that. to honest the circuit is not worth the trouble, and i have discontinued using it and i have not seen much difference in MPG since. but the throttle is more sensitive now and you have to feather it like it's made of eggshells.

also i have not seen much of a relationship between low engine load and poor MPG. in fact it has been the opposite for me. you can see in the video im in about 35% engine load and getting near 40mpg. if my engine load was higher, say 48% i would be getting 30mpg only. i only monitor LOD during acceleration to keep it in 80-90% range at 2500rpm.

[turbovr41991]

Good stuff! Congrats. I love reading sucess stories with lean burn. It is a shame it produces more NOx though.

[ever_green]

ya thx. well the car does have 2 cats

[ever_green]

i am fine tuning my AFR it to balance it between fuel economy and power. so far the results have been promising with 37mpg last short highway trip with NO hypermiling tactics. i'm talking just plain old cruise control set to 70mph. This included some slow downs and accelerations due to traffic:






keep in mind my car is rated 20/26 EPA. The car runs mostly 14-15 afr in cruising but sometimes lower to control temperatures and etc. here is a video of afr:

AFR and Long term Fuel Trim

http://www.youtube.com/watch?v=ytKuvLXR4QE

[cRiPpLe_rOoStEr]

The best my dad ever achieved with his 2.0L stickshift Impreza was 35 MPG at 43 MPH, using Brazilian gasoline with 20% ethanol.

[ever_green]

yes i used mid grade 89 because thats what my car is tuned for but it has 10-15% ethanol. i can get 91 0% ethanol but thays 8 cents more per liter and it will end up costing me more anyway.

[kyanox]

I hate to revive an old thread, but can you share your rom and romraider def with me on this one? I'm trying to ecotune my 08 impreza 2.5i AT and i'm running into issues getting the car to run lean without causing issues.

Thank you in advance.