Re: Milage

Can someone explain to me why my 1998 Audi A4 2.8 liter Quattro (6-cylinder engine) gets the same, usually better, mileage than my other half's 1999 Subaru Legacy Outback 2.5 liter (4-cylinder engine)? They're both AWD vehicles, and mine has the bigger engine (granted, it uses the premium fuel, whereas the Suburu does not), so I don't understand why the Subaru doesn't get better mileage.

I have a 2003 Outback wagon I drive around Vancouver. I get 9.9 to 10.2 litres per 100 kl. A little under 30 mpg (Canadian) Havent check highway milage yet.

I have an 03 Legacy GT sedan with 4EAT. Around Calgary, I get ~ 25 mpg. On a recent return trip to Vancouver, I got no less than 30 and up to 32 mpg at ~

I have a 2003 Impreza TS (2.5 eng) with 4000km. I live in North Eastern Alberta. Mostly small city and rural driving - average speeds of 50 to 80 km/h. I'm getting about 30 mpg (imp gal measurement).

Cheers

Scott

Thanks from the 'front lines' of real world driving.

I am considering the same model as you.

Brian

I'd postulated on this before, and I've come to the conclusion that the extremely oversquare bore/stroke ratio is a major culprit. My bet is that a heat-reflective, ceramic coating on both the piston crown and combustion chamber surface would yield a 10% improvement in fuel mileage (and raise the effective compression ratio) as a result of increased thermal retention. This would work on any engine that has exposed aluminum surfaces in the combustion chamber, but would be especially beneficial to engines with a greater than average amount of heat-sinking area.

-Danny

extremely oversquare

ceramic coating on both the

in fuel mileage (and raise

retention. This would work on any

would be especially

Being that cam timing (especially fixed) can have such a profound inpact on emmissions, manufacturers like Subaru find themselves in a bind by having to make serious compromises. I'd have to agree with you that the overall performance of the 2.5 could be a fair amount better with a cam change tho. The cam that's in there seems to have the tendency to reduce effective cylinder filling below 3500 RPM, yet seems to also snuff the top-end breathing out past 5500 RPM. The torque band seems a little narrower than it could be, especially for the weight of the vehicle.

Mmmm... I'd say another .100 lift, 10' more duration, a slightly wider lobe separation angle, and maybe a degree or two of overall cam advance would would both broaden the torque curve as well as let the top sing out to 6k. Ports might have to be cleaned up a bit too. -Danny

wrote:

compromises. I'd have

amount better with a cam

effective cylinder filling

RPM. The torque band

separation angle, and

torque curve as well as

On the other hand, even their engines that do have variable valve timing (AVCS) don't get good mileage in the US (e.g., Forester XT). It may be emmissions related, since their 2.0l engine with AVCS in Japan appears to get great mileage.

- D.

Answer is obvious: you may be a better driver than your wife. Mine has always driven a stick shift and refuses an automatic, however I have often noted (from the passenger seat) she simply does not shift like a man. I often have to gently remind her perhaps it's time for 5th gear.