Just traded in my '08 Subaru OB (took a 2 year hiatus from Volvo's) and bought a '09 S60 2.5T AWD. I am under the impression that most stock air filters are pretty efficient BUT in the interest of maximizing fuel economy, is there an air filter out there that really could tweak my fuel economy? (Assuming that I drive to achieve maximum mileage) I am also interested in the next generation of LRR tires for the S60. I'm thinking by next spring the tire companies will have made additional improvements in this area. I ran Goodyear Fuel Max tires on my OB, and again. driving in a fuel efficient manner, I was able to get a consistent 32/33 mpg! Any fuel efficient mods appreciated!! My last Volvo's were an S40 and a 240. My wife is on her 4th wagon and 3rd X/Country. Thanks, Bill

 

I run the BSR intake setup, which is basically an aluminum heat shield and cone filter. I didn't notice an increase in fuel economy when I installed it but it is less restrictive than the factory air box. A K&N filter may be what you're looking for, but again I doubt you'll see much gain in fuel economy, maybe 1/5th of a mpg or so. With my setup and Potenza G019 tires (which are awful) I can run 31mpg at 70-75mph but the cost to do all i've done wouldn't be worth the money saved by adding 4-5mpg.

 

I'm not aware of any differences between the '07 and '09 S60 2.5T as far as the engine goes, so here's what I did with my '07.
After buying the car last year, I did all regular tune up procedures and then a few mild upgrades.
Before tune-up and upgrades, it was getting around 21.9 MPG average for all around driving. After tune-up, but before upgrades, it was getting about 22.2 MPG average.
The upgrades I did:
I used EuroSport Tuning's Filter and heat shield kit (aFe):Eurosport Tuning: Ultra-Flo Air Intake System - 2.4T, 2.5T & T5 2001-2007
The filter is very high quality and it is nice to hear the turbo breathing... sounds like Darth Vader. I had to put a piece of rubber tubing under the heat shield to brace it from engine torque, which was causing the air tube coming from the grill to separate.

I also got the following items from iPd in Portland:
ipd HD Polyurethane Transmission Torque Mount
Upper Engine Stabilizer Mount & Bracket
ipd Strut Bar Mount Conversion Kit
After applying these upgrades, I now average 23.3 MPG with a lot of small road driving and a heavy foot. Increased highway driving takes that up to 23.5.
A lighter foot and more highway will certainly put it into the ~25MPG range.
I'm glad I did those upgrades. My old transmission torque mount was shot and took about 5 minutes to change it... super easy!
The upper engine torque bushing mount took more patience, but also was a fairly easy job.
The torque bar/strut tower brace conversion kit was super easy to install and made that torque bar completely rigid. I used to be able to twist it with one hand before.
One thing to keep in mind. Each of those bushing replacements increases idle vibration by a noticeable amount, especially the strut bar conversion kit. After about 1000 miles the vibration settles down quite a lot, but for a while it was like sitting in a massage chair while at stop lights.
Also, I had applied iPd's Heavy Duty ignition coils and Denso IK-22 iridium spark plugs... they helped a bit too, but those bushings did the most improvement.

 

I forgot to mention... the user submitted photos on iPd's pages for the upper engine mount bushing and the strut brace conversion kit are pictures I took of the installation on my car.
The strut brace conversion kit can be mounted one of two ways, with the iPd logo facing up, or with it facing down. Logo facing down gives a more rigid mount, which is what I did.

 

Yes the bushings really do help add mpg to any style of driving, one thing to be aware of though is that you need to tighten them all down with the engine running and the car in gear. This takes away almost all idle vibration. Besides from engine mounts and tires the only other large improvements would be removing excess weight. If you have no use for your back seats on long trips then remove them, it saves 80-90lbs and gets you a little over 1 mpg. If you really get serious then you can turn your AC/headlights/radio off, which would allow you to save even more...but at the cost of comfort.

 

I'm pretty anti oiled fiber filter for cars with a MAF sensor. They are great, but the oil will (regardless of how good you are at oiling the filter) coat the sensor filament and then over time fine dust particles will bind to the oil, and your MAF readings will be off. Some people even blame the oil and dirt on their MAF completely failing, but I'm not sure I believe that yet. Regardless, I recommend dry flow air filters, whether it's the stock paper media or aftermarket like an AEM dryflow filter.