Some people asked us what's so new with the engine of the 2015 Yamaha YZF-R1. First the redesign started at the crossplane-crank engine that's been significantly lightened but also tweaked to provide the top-end performance that the previous-generation YZF-R1 lacked. The added performance begins at a 24-percent-larger airbox and air duct that runs through the steering pipe to pressurize the airbox similar to how air is fed through the Yamaha MotoGP bike.
The YCC-I variable intake system has been updated so that funnel length at high rpm is 20 percent shorter than before, plus Yamaha has straightened the injector spray angle so that fuel sprays to the back of the intake valve rather than toward the port walls for improved combustion. Intake and exhaust valves are larger, by 2mm and 1.5mm, respectively, placed at a narrower angle, and work through machined combustion chambers that are intended to increase compression ratio consistency from one cylinder to the next.
Bore and stroke jump from 78.0 x 52.2mm to 79.0 x 50.9mm, while compression ratio climbs from 12.7:1 to 13.0:1. New camshafts provide increased valve lift, 0.6mm for the intake valve and 0.7mm for the exhaust valves, and work on rocker arms that enabled Yamaha to use lighter valve springs. Forged aluminum pistons are 8.5 grams lighter despite the 1mm increase in bore size, and titanium fracture-split connecting rods are 40-percent lighter than the steel parts, which contributes to added high-rpm power. The cylinder is offset 2mm toward the exhaust side so that the pistons won't push against the cyinder wall on the power stroke. Yamaha has also reduced crankshaft inertia by 20 percent for a quicker-revving nature, while also moving the balancer weights. The engine is 33.02mm narrower at the crank axis and weighs 4 kilograms less than the outgoing engine, magnesium engine covers and aluminum bolts help here a lot.
A new transmission has revised gear ratios for first through sixth gear, first through fourth is slightly lower total ratio at rear wheel, while a new assist and slipper clutch is 19-percent lighter and uses just three springs.