Non-Oem Plugs For The R1100/850 Oilheads - BMW R850 Maintenance Manual

2. The average torque and horsepower, across the entire 4th gear roll-on range,
3500 - 7500 RPM, was improved by increased valve lash.
2. Increased valve lash and advanced timing (9 degrees) netted an average
torque increase of 3.1 and an average horsepower increase of 4 over
stock valve lash and stock timing (6 degrees).
Non-OEM (Original Equipment Manufacturer) Plugs for the
R1100/850 Oilhead - Rob Lentini
The BMW Internet lists have been ablaze lately over spark plugs! Why has a
simple item been such a popular subject of discussion? Here's why...
Many of you are aware (sadly so!) of the surging that is common in many of the
R1100/850 series BMW Oilheads. This subject itself has been one of much
discussion and I took some time to investigate it myself on my personal '94
R1100RS. My work led to my four part series on "R1100 Fuel
Injection/Surging/Fixes", and later my "Zero=Zero" effort on getting the Throttle
Position Sensor (TPS) optimized for best performance. However, along the way
in doing this I learned that spark plug performance and selection can play an
important part in overall performance of the R259 Boxer.
Being a thrifty person (a nice way of saying "cheap"!), I have habitually looked for
aftermarket service item parts that meet or exceed OEM requirements but are
more readily available and less expensive. Wear items like brake pads, oil filters,
air filters, and spark plugs are open-discussion items for me and it wasn't long
after my Dec '95 purchase of a used '94 R1100RS that I began the process that
had ended with the sale of my '87 K75S.
I'd had good luck with Autolite 4153 plugs in my K and I was eager to avoid the
extravagant price of the OEM Bosch plugs of about $10 fame. So armed with my
Autolite and Champion spark plug catalogs, I cross-referenced to the point of the
best possible match: Autolite 3923 and Champion RC9YC plugs. But wait;
here's the difference.
The '94-spec OEM Bosch plugs for the R1100RS are FR5DTC, a unique three
ground electrode setup that surrounds the center electrode from the side. The
Autolite 3923 and the equivalent Champion RC9YC plugs are standard single
ground electrode "over" the center electrode as many of us are familiar with.
Would these "standard" plugs work?
I took the dive, bought Autolite 3923s, set the gap to the BMW specification of
.031" or .8mm, and went for a ride. They worked great! I even noticed smoother
power characteristics and somewhat less surging, and this was in early '96
before I began my above-mentioned Injection/TPS experiments in earnest. So
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