MotoGP

My February 2007 issue of Cycle-World (which contrary to the fervent wishes of my macho brother in Boston doesn’t worship Harley-Davidson, and is therefore reprehensible) has an interesting article on MotoGP racing, and the motorcycles therein.
The article was written by Kevin Cameron, the best writer the magazine has on its staff, primarily because he’s technically-oriented.
Last month he did an analysis on the S&S X-Wedge, and explained its engineering-superiority to the Harley-Davidson clones.
It was very interesting to me, since it explained the limitations of the hoary old Harley design; that S&S decided to improve it.
MotoGP replaced 500cc two-stroke that was burning up the motorcycle grand-prix.
The 500cc two-stroke had turned into a grenade; it developed so much explosive power, which hit like a light-switch, it burned up tires and/or spit riders off.
MotoGP, 990cc four-stroke, was more civilized; except it was burning up tires too.
So this year MotoGP was reduced to 800cc, but the manufacturers responded by making their motors as powerful as 990cc.
How did they do this? Rev the motor to 18-grand, at which point it generates as much power as 990cc at 15-grand.
All but Yamaha are doing V4s; Yamaha’s an inline four.
Even Ducati is a V4, but has desmodromic valve gear.
Which is why I find the article interesting, because one of the manufacturers, Suzuki, has gone to pneumatic valves.
Mechanical valve-actuation, with return-springs, has limitations.
The opening ramp of a cam has to be easy enough to not bounce the follower off the cam. Steep enough the valve bounces into the ozone.
Tight return-springing can offset that, but invites deterioration of the cam-surfaces and the followers.
Desmo is mechanical too, but adds a second cam to close the valves (instead of return-springs), and makes the followers follow the cam.
My 1980 900SS Ducati was desmo, although only single overhead-cam and two-valve. Desmo allowed the opening-ramps to be steep, so even the idle was ground-shaking.
I’m sure the straight-through mufflers contributed, but a HUGE-AAAH intake-charge was being processed by the motor.
Both Desmo and pneumatic (I think) dispense with return-springs. Pneumatic is common in Formula-One auto-racing.
I can’t comprehend pneumatic valves — I suppose it’s reaction to how sloppy air-brakes are on a train.
Air-brakes were a HUGE-AAAH advancement over the individual braking of “brakies” riding the car-tops — in that the train-engineer could brake the entire train (instead of having to rely on “brakies” sliding over rocking, icy car-tops).
But application of the brakes over an entire train takes minutes — requiring compensation for its engineering limitations. In fact, passenger-trains rely on electrical actuation of the air-brakes in the cars, so that braking-action is much quicker, and smoother, when induced by the engineer.
If passenger-trains had the same brake-gear as on coal-cars, the train would bunch up as the lead-cars began braking. SLAM-CRASH; throw the passengers on the floor.
My impression of pneumatic valves is that actual activation could be erratic — that activation would be sloppy and imprecise.
But I guess it’s more precise than mechanical — we’re talking about micro-management.
I had the same feelings about fuel-injection. Volkswagen’s original fuel-injection (the FI on my Dasher and Rabbits) was continuous; i.e. the FI was always pumping gas, including when the individual cylinders didn’t need it.
But pollution-requirements required more precise gasoline metering — off-on — such that the FI delivered gas to a cylinder only during the intake-stroke.
The idea of metering out such precise amounts of gasoline at such high speeds was incomprehensible.
But that’s what’s done; technology has advanced to the point that precise off-on metering can be done at thousands of cycles per minute.
So the idea of pneumatic valves, though incomprehensible, is doable; and better than mechanical — especially if it dispenses with return-springs.