mileage just disappearing

[serialk11r]

Originally Posted by arcosine

19 mpg, Subarus suck at mileage, always lower than sticker. It's that stupid way too over square boxer engine.

Wouldn't be so quick to blame the oversquareness. When they released the FB20 they said they had reduced friction 29% from the EJ20. 29 whopping percent. That is huge. Of course, having a more modern combustion chamber design helps, but we all know how much friction has to do with fuel economy. 29% is probably on the order of removing all pumping losses.

[arcosine]

Not quick to blame, I had one a long time ago. You can reduce the friction all you want, but if the heat escapes through all that combustion chamber surface area, you loose.

[ever_green]

tire pressure is good, my exhaust smell is actually worst off now. my whole driveway smells like a gas station when i start it up lol. i thought oversquare allows for lower friction losses?! one reason why maybe my BSFC sweetspot is wide from 1500-4000rpm at %80+ load? i think this has more due to do with the all-wheel drive and slightly large fuel pump and 500c injectors. also from what i have read the AVLS system is almost 90% of the time in high lift mode. and as for heat as i said i never see it go below 88'c wether at idle or highway cruising. i'm sure this engine just doesn't like gas asdditives, i mean i had no problems getting 33mpg in summer highway, now when i cruise it just doesn't go above 27mpg. reminds of running e85 vs pure gasoline in fuelflex cars. i think maybe my expectations are too high...

[bestclimb]

Originally Posted by ever_green

my whole driveway smells like a gas station when i start it up lol.

I have had this with a bad signal for intake air temp. Car going way to rich during start.

[ever_green]

Originally Posted by bestclimb

I have had this with a bad signal for intake air temp. Car going way to rich during start.

bad as in replace or clean? is that part of the MAF sensor? scangauge shows intake temp to be couple degrees higher than outside temp.

[bestclimb]

Wire had a brake in it. The computer showed -40 (according to Ultra gauge) MAF is separate but the temp probe samples the same air and the computer corrects the MAF for intake air temp(this was on a the Ford though most MAF systems are similar). If your scan gauge is showing a close number I would not suspect a problem there.

The smell of fuel is pretty indicative of a very rich mix.

[serialk11r]

Originally Posted by arcosine

Not quick to blame, I had one a long time ago. You can reduce the friction all you want, but if the heat escapes through all that combustion chamber surface area, you loose.

Yea well, either way doesn't hurt to have double digit percentage increases in mechanical efficiency AND combustion efficiency (Mazda is undergoing a similar fuel efficiency leap lol)

But don't hate on short stroke engines, the BMW S65B40 for example is a beauty. Piston and head design matters more than dimensions anyways. Mazda Skyactiv engines may have good bore/stroke ratio, but the extremely high compression ratio usually gives the combustion chamber a bad shape, so they gave it that rather deep piston bowl. In fact the low compression ratio on the EJ engines probably helped the heat rejection (at a greater efficiency penalty of course).

[LeanBurn]

Sometimes when fuel economy takes a dump in the winter it makes me want to drive much faster than normal just because I know its going to suck anyways...so if I pass you going 120km/hr compared to my usual 90 km/hr...that is why.

I keep all other items in place though..grill block, tires at 40 psi and block heater when below-15C...the entire year round..

[arcosine]

I don't like over square engines. Fine for performance, but not fuel economy. combustion surface area increases buy the bore squared. 100 mm bore has 50% more area than a 80 mm bore.

• Prius:
1,497 cc 1.5 liters in-line 4 front engine with 75.0 mm bore, 84.7 mm stroke, 13.0 compression ratio.

Honda CRX HF: Engine Bore/Stroke 75.0x84.5mm

Saturn S series: 82 Bore× 90 mm stroke

Honda Insight: 72 bore × 81.5 mm stroke

Subaru EJ25

Displacement: 2457 cc
Bore: 99.5 mm
Stroke: 79.0 mm

[user removed]

Originally Posted by arcosine

I don't like over square engines. Fine for performance, but not fuel economy. combustion surface area increases buy the bore squared. 100 mm bore has 50% more area than a 80 mm bore.

• Prius:
1,497 cc 1.5 liters in-line 4 front engine with 75.0 mm bore, 84.7 mm stroke, 13.0 compression ratio.

Honda CRX HF: Engine Bore/Stroke 75.0x84.5mm

Saturn S series: 82 Bore× 90 mm stroke

Honda Insight: 72 bore × 81.5 mm stroke

Subaru EJ25

Displacement: 2457 cc
Bore: 99.5 mm
Stroke: 79.0 mm

And the most efficient mega diesels in giant ships have a 3 foot bore and a 9 foot stroke, with a scotch yoke to eliminate piston side loads. Longer stroke means a better lever. Not many short stroke engines are in the top percentages for best BSFC.

regards
Mech