Motus MST-01: is direct injection the next big thing?

Published: 16 March 2011

Motus is keen to make hay from its head-start on gasoline direct injection (GDI), which features on their new MST-01 sports tourer, the first time the technology has been seen on a four-stroke bike.

It’s credited with much of the car industry’s recent power, efficiency and emissions gains so it would appear set to spread like a rash over new models from 2012 onward. Only it won’t.

Run at its chief theoretical advantage for bikes, stratified direct injection allows more air into the combustion chamber, a cooler fuel-air charge and higher compression.

It also makes for less wasted power at part-loads, thanks to allowing a wider throttle opening for a given amount of fuel (lean-burn mode).

But it isn’t a trend about to spread to more conventional bikes due to their higher engine speeds, as Lotus Engineering’s Dave Blundell explains: “Injecting directly into the cylinder head, GDI relies on having enough time for good fuel preparation.

"To get the maximum benefit you’d need prohibitively expensive ultra-high pressure stratified injectors – higher than 200 bar. And 8000rpm is starting to push the boat a bit anyway, so engines with low inertia valve trains which can rev beyond aren’t suitable candidates.”

The Motus runs 138 bar, non-stratified (‘homogenous charge’), injectors. Says Blundell: “Any gains in performance from this are unlikely to justify the added cost and complication when compared to a good port fuel injection system.

"But the Motus’s push-rods do leave room for near vertical installation of the injectors, so there are some good reasons for using a simple cost effective two valve layout in this instance.

"And the prestige of being the first is another matter.” Just don’t hold out for it on your next VFR.