6 THINGS YOU NEED TO KNOW…
Less is more
Engines don’t get more powerful by magic. It comes from reducing inefficiencies: making valves lighter, cutting rotating mass, reducing friction, and so on. We worked on making moving parts lighter – for example, using special steel for the exhaust valve rocker, and changing roller bearings in the conrod for plain ones.
The lower balancing shaft works against the oscillating masses of the crankshaft and big end. But that also creates momentum, and so a force. The upper balancer works against this force. There was a lot of brain work on this because of the leverage: if the balancer is a bigger distance from the crankshaft, its weight is less; shorter distance, more weight. And it must rotate at the same speed as the crankshaft. We mounted acceleration sensors in the engine and found vibration was reduced by half.
Breathing is important to cut the pumping losses. But you must also remove the oil mist from the air inside the engine. We used the upper balancer weight to solve this problem. The engine breathes through a hole in the balancer, but because the balancer rotates at crankshaft speed the oil droplets in the air are flung away by centrifugal force.
The piston is 105mm, 3mm wider than before, and the stroke is 80mm, 4.5mm less for higher rpm and a greater piston area. The piston is milled to reduce weight. The DLC piston pin coating saves the weight and volume of a roller small end. It’s hard control emissons with a very flat combustion chamber, so we use twin plugs.
This is a closed chamber connected to one inlet port. The resonance it creates helps on part-throttle by modifying the inlet pulses. It also allows us to run different ignition timing on the two plugs, because the second plug’s spark is in the ‘shadow’ of the first. It was not necessary to regulate the volume of the chamber, but to place it at the right angle to the inlet tract.
When you start the engine there is a little rattle at first. That’s because we use a hydraulic system for the cam drive, and for the first two seconds there is no oil pressure. On a mechanical tensioner, there is no ‘give’, so there is a lot of force on the timing chain but this way, there is less stress. Accuracy at high rpm is not a problem because with the plain bearings we are working with very high oil pressure.