GSX-R1000 ABS and GSX-R1000
Circuit of the Americas
April 24, 2017

by Sam Q Fleming

Resonance.   Although we might be reaching the beginning of the end of the internal combustion age I am still captivated by the depths of the physics at play. Twenty-eight years ago my Army Of Darkness teammate and I watched in bewilderment as a cloud of raw fuel formed over the carburetors of a screaming FZR400 strapped to a dynamometer. We had spent countless nights digesting Phil Irving’s Tuning For Speed but we were totally unprepared to witness a physical manifestation of intake waves.

When an intake valve opens, a sound wave begins to progress back along the intake tract. It continues until it reaches the end of the velocity stack, at which point it gives up some of its energy but, like a wave bouncing off a swimming pool wall, another wave is reflected back towards the intake valve seat. That wave carries air on the front of it like a surfer. If the intake length is the proper length, that second wave will reach the intake valve seat just as the intake valve is closing. The piston has long since begun its compression stroke so the pressure in the cylinder is rising, but the intake valve is still open. One would expect the intake charge to begin reversing its flow but inertia is still pushing more air into the combustion chamber. Just when cylinder pressure is about to overwhelm the intake tract pressure, the reflected wave from the tip of the velocity stack arrives and stuffs a tad more mixture into the cylinder as the intake valve is closing.

Aprilia Armada
Circuit Of The Americas
April 24, 2017

by Sam Quarelli Fleming


“That’s the girl I remember!” I thought as I tapped the apex curbs of COTA’s turn 5. COTA has a series of S turns which are entered all spun up in 3rd gear and which produce tremendous gyroscopic forces between the crank and the wheels. I had spent the first 45 minutes of the day on the RSV4RR and had pushed wide through the second S on each lap. This was disappointing, as I had reserved a special place in my heart for the RSV4 ever since we had shared one magical Italian day at Misano two years prior. I had tried raising the rear of the bike on the RR to try to rekindle my feelings but each lap required a soft lift of the throttle to get back to the apex of Turn 5.

But my first time through that sequence on the RSV4RF, all the old feelings came pouring back. Apexes came flying up to us like friendly swallows while 200bhp blurred the rainbows down the straights. When the peg feeler and muffler carved our memories with indelible scratches in COTA’s expensive racing surface I couldn’t help but smile at how this joyful manifestation of Italian culture could be taken to the edges of its incredibly high performance envelope, on an out lap.

Apparently I have expensive taste.