Tech: Inside the Busa’s engine

Stronger than ever, new Busa promises to be a gift to tuners

‘Power is down but potential is definitely up’

When a new version of long-running model is released the expectation is that power will rise – but with the 2021 Hayabusa, Suzuki have ploughed development into an engine that actually makes less peak bhp than before.

Straight off the showroom floor, the 2021 Hayabusa (see p34) is fractionally down, but importantly for a bike that’s formed the basis of a global tuning industry, it holds the prospect of even greater extremes of performance with the judicious application of aftermarket parts.

Suzuki’s engine changes focus on two fronts. First is meeting Euro5 – a two-step jump from the old Busa, which was removed from sale here after missing Euro4. Second is making an engine that’s already legendary for its strength even more rugged and reliable.

Look at the spec and you might think the inline four is unchanged. The 81mm bore and 65mm stroke are unaltered, as is the 12.5:1 compression ratio, but those bare figures belie the depth of the alterations made. In fact, the familiar-looking cases hide new camshafts, new pistons and rods, a revised crankshaft, a modified transmission and a host of smaller updates aimed at reducing emissions and boosting durability.

That focus on reliability includes revised oil passages that boost flow and pressure at the crankshaft by 54%, stronger conrods, longer needle bearings in the transmission to reduce wear, a redesigned tensioner to keep better control of the cam chain and even redesigned threads (rolled instead of cut) on the crankcase cover and a revised tightening procedure for the engine case bolts. Tiny tweaks based on years of accumulated knowledge.

From an emissions point of view, the first change is reduced valve overlap - the period where the intake and the exhaust valves are both open. That’s been a running theme in Euro5 updates; lots of overlap helps achieve peak power at high revs but also lets unburnt fuel into the exhaust at lower engine speeds. Other changes include longer intakes with smaller-diameter throttles, new injectors and a reworked exhaust.

Once tuners get their hands on the new engine – swapping camshafts, changing throttles and exhausts, even adding turbos or superchargers–the emissions reducing elements will soon be forgotten, leaving just the stronger base engine design to provide a platform for even more stratospheric performance.

Pistons and rods The new pistons are each 26g lighter and each conrod loses 3g, reducing vibration and stresses on the engine. From intake to exhaust, the changes add up

Injection and intake New angled secondary injectors bounce fuel off a plate in each intake to improve atomisation and get a better burn, while the airbox is larger and fed by freer-flowing ram air ducts. Exhaust A new two-stage system of three catalytic converters – one in the collector and one in each end can – replaces the old single-stage setup which had to cats in the collector. Combustion chamber Although the valves are unchanged the Twin Swirl Combustion Chambers are reshaped to improve ignition, increasing the flow coefficient by 5%, increasing combustion efficiency. Camshafts Increased valve curtain area improves burn Exhaust valve lift is increased and they open faster than before, with wider cam lobes added to make sure the more aggressive profile doesn’t increase wear.