Originally Posted by Duke2.6

Any M103 will make substantially more low end torque and noticeably better fuel economy if you remove the R16/1 resistor.

This will create the most aggressive centrifugal spark advance curve. I can even get away with 87 PON fuel on my 190E2.6 five-speed as long as the engine temp is about 80C and ambient is no more than 70F. Above these temps I pick up a little transient detonation on upshifts, but it's easy to drive around by shifting higher than my normal 2000.

With the above setup it may fail field emission tests. The best set up for emission testing is to short the R16/1 plug. This will yield the slowest centrifugal curve, which lowers peak combustion temperature (less NOx), but increases EGT to keep the catalyst hotter. (But it won't get out of it's own way below about 2000.) Blocking the vacuum advance signal line will further aid in passing emission tests.

With the OE 750 ohm resistor I got about 18-20 MPG around town and high 20s on long freeway trips at 75-80. With the R16/1 removed around town fuel economy shot up to 22-24 MPG (about the same highway), and I can drop it into fifth at 35 MPH. Before, fifth was unusable below about 45 MPH. These are the effects of a spark advance map optimized for performance and economy rather than emissions.

I've known a couple of folks with 300SEs. They are very nice "town cars" with a first gear start. Most find the engine too "busy" at highway speed, but the engine is very smooth and quiet. They just get upset about the high tach reading.

There's lot's of information on the R16/1 resistor, including where it's located on your model, in the archives.

Duke