New Tech
By Anton Largiader

Valve drive
When the R1100 series was created in the early 1990s, the camshaft moved from the engine block into the cylinder heads. Gone were the long pushrods and heavy valves of the Airheads, but the change wasn't all that radical. The cam was still 'under' the valve train. We still had pushrods (although they were very short), lifters and steel rocker arms. Shorter pushrods and lighter valves helped bring the maximum engine RPM from 7250 to 7900 RPM, and refinements brought this to 8800 RPM for the R1200S, which retained the basic design of the first Oilhead.

Simple inertia of the moving parts is the RPM-limiting factor. The cam throws the parts in one direction and spring force pushes them back. If they move too fast, they 'catch air' at the end of the cam lift and float. When this happens, the valve can still be off the seat when the piston comes around expecting it to be closed. Wham. Another downside is that the valve can bounce once it slams closed, damaging the sealing surfaces and allowing valuable combustion pressure to escape. This conventional boxer configuration is shown in Figure 1.

Reduced component weight is the most common approach to this problem, and with the HP2 Sport BMW has gone this route with the finger-follower design that we first saw on the K1200S. As shown in Figure 2, there's a cam, a follower, and the valve. That's all. And since the follower doesn't have to do actually be strong, since it's not doing much more than being sandwiched between the cam and the valve (thus protecting the valve from nearly all of the sideways forces that the rotating cam would otherwise impart) it can be very light. With the minimized valvetrain weight that comes with an overhead cam design, the maximum RPM of the HP Sport is 9500. Figure 3 is a slightly different view of the HP2 Sport configuration.

Why is this so important, you ask? Power is essentially the product of torque and RPM. Torque generated at a given RPM is dependent on things such as proper engine breathing, but if you can get that same torque at 5% higher RPM, you have 5% more power. Keeping the valves on the right path at high RPM is an integral part of this.

Transmission changes
Two significant changes come with the HP2 Sport: a close-ratio gearbox and a quick-shift.

Close-ratio gearboxes have been around for a while, but the last one produced by BMW was for the Airheads. On that one, first through third gears were 'taller' than normal, resulting in a bit more clutch slip off the line but in return, giving a greater likelihood of finding the perfect gear for a given corner on the track. After all, no racetrack corners are suited for a typical first gear.

With the HP2 Sport, the close-ratio gearbox is back, but in reality it is very similar to the standard gearbox. First is about 10% taller, the next few are about 4% taller, and top gear is the same. In the older Sport gearbox, the differences are much more pronounced.

The second big change is a quick-shifter. This is not new on racetracks, but it's the first time a production motorcycle has been so equipped. A sensor in the shift linkage detects the rider moving the shifter, and the engine ignition and fueling are momentarily cut to allow the gears to engage under full-throttle, clutchless upshifting. Commercially available quick-shifters are incorporated with the Dynojet/Power Commander fuel systems, or available separately. San Jose uses a system by Tectonics on their R1200S racers. Aftermarket systems are user-programmable for shift delay time, but the HP2 Sport system is integrated with the BMS-K engine management.