Originally Posted by Duke2.6

No, the oxygenate is ETHANOL, not methanol. No manufacturer has approved methanol because it's corrosive. All California gasoline has 10 percent ethanol by volume, which is the EPA limit, and most other areas of the country have ethanol, but the amount may be less.

The advertised CR of my '88 190E 2.6 is 9.2:1 and the required fuel is "premium". That's not a very high CR, and I have been successfully using 87 PON for a decade, even after removing the R16/1 resistor to quicken up the advance curve, which yields noticeably more low end torque. With the standard US model 750 Ohm resistor, fifth was unusable below about 40-45 MPH. Now it's usable down to 30, and around town fuel economy is up to 22-24 from 18-20.

For emission testing I short the R16/1 socket and plug the vacuum advance hose, which yields the least aggressive spark advance map and lower emissions, but the engine is totally gutless below 2000. HC was always close to the limit. Now it is half and NOx is down 90 percent, so I no longer have to sweat out emission tests.

If ambient temperature is no more than about 70F and coolant temp holds at 80C it will pull from 1200 in fifth, about 30 MPH (It's a five-speed manual) with no detonation. If ambient or coolant temps are higher I simply upshift and downshift at higher revs to avoid loading up the engine below 2000 to avoid detonation. Since I only drive the 190 during winter months, detonation is rarely an issue.

It's easier with an automatic because the torque converter won't allow the engine to load up below converter stall speed, which is about 2000.

Detonation is primarily a low rev/high load issue. Modern cars can retard advance if detonation is detected. This may reduce low end torque and result in less snappy acceleration around town, but no one I have ever recommended to do this who did it noticed a difference.

Duke