I really did a lot of research on this as I have been know to loose sleep over such questions. This applies to US market as I don't know if this stuff is available in Europe/Asia:<P><BR>1. Best Gas: Chevron Supreme. 91-93 Octain. Reason, Techron, the only proven additive that keeps engines clean, very clean.<P>2. Best Air Filter. Toss up between K&N and Amsoil, both reusable and both high airflow.<P>3. Best Oil. Amsoil (specifically, Series 2000 0W-30). Very expensive, but so is a $40,000 wagon. Reason, ASTM tests done independant of any marketing hype, Amsoil is the best in most important charactoristics..... Kenetic Viscosity, Film Strength (3300 psi), Cold pour point, and Flash point. Also, if you want you can run it to 1yr/35,000 miles with out changing the oil (so long as you change the filter every 7500 miles) as the additives are very robust.<P>I personally stick to Volvo's 7500 just because I can justify the $8 per quart at that interval. My 97 960 which is now out of warrantee goes 6 months 15000K between oil change and a new filter every 3 months or 7500.<P>4. Oil Additive. None!<P>5. Gas Additive. Chevron Techron (only every 3000 miles) <P>6. Wax - many are good, as long as they are carnuba and I like Zymol and Mcguires (sp?).<P>7. Leather cleaner - Zymol. Reason, doesn't leave a film or make it shine like the cheap stuff.<P>Pardon my bad spelling and good luck.<P>Sam<BR>
One more vote for Chevron. We had a Honda Accord that at 100k miles would NOT stop pinging (designed for regular gas, and we tried all the way up to super). The dealer retarded the timing to the bottom of the specs, and it would still ping. After studying up on additive packages, I first dumped techron in the tank, then began ONLY filling with Chevron regular (right after they began including Techron in the regular gasoline). Four tankfulls later (and two more Techron boosts), the car never pinged again. And we drove it another 100K miles. Still going today (sold it to my friend) with 250k, and still isn't pinging.<P>
Based on consumer articles that I have read, the gas you use is really not the issue versus the octane you use. I would stick with a major brand but any of them should perform well. As for the oil, you will get lots of different opinions on it. If you have a turbo and drive it hard then you may want to consider changing about every 5k miles. You can go 7k but with hard driving you really burn up the oil a bit quicker. Whether you want to use synthetic is up to you but it is not recommended that you use it if you have been using regular oil for years. If you want to use this, then use a very light oil to run through engine and clean it out before using synthetic. If you change it regularly (5k-7k) you should have many happy miles.