Engine Downsizing

ENGINE DOWNSIZING

IGNITION

TDC

SMALLER ENGINES AND HYBRIDS IN CARS ARE BIG. WHAT’S NEXT FOR MOTORCYCLES?

KEVIN CAMERON

Engine downsizing is huge in the auto biz because they have the new 54-mpg CAFE fuel economy standard looming over them. On average, cars use only 10 to 15 percent of their installed horsepower in daily use, so it makes sense to take that horsepower from the smallest possible engine. The smaller the engine, the smaller its losses from bearing and piston-ring friction and from pumping loss. Using a classic 427 big-block to make 35 hp for a trip to Starbucks isn’t on any more; churning five giant 3-inch main bearings, eight 2.5-inch rod bearings, and acres of pistonring swept area eat up a lot of power in oil-film shearing even at idle. To say nothing of all the pumping-loss vacuum created at such low throttle.

So the industry’s answer is smaller engines, powered up to the required level by turbocharging—just as the late Smokey Yunick predicted years ago.

A little turbo 2-liter four has a lot less friction and can still move the freight.

This is not happening in bikes, and I can think of at least three reasons why:

1) The EPAhas not yet decided to regulate motorcycle fuel consumption.

2) Motorcycles are expensive enough as it is, without writing 100,000 lines of turbo controller software.

3) No one has yet produced a turbo motorcycle that can match the predictable, smooth power delivery of today’s conventional sportbike engines.

History suggests that the EPA will eventually get around to motorcycle fuel consumption, but because the fuel used by bikes is a tiny fraction of that consumed by cars and trucks, regulation tackles the big emitters first. In the meantime, ain’t we got fun?

When it comes to cost, motorcycles already employ premium technologies, such as advanced suspension dampers (it was Geoff Fox who showed the Indy car people what they were missing by

not using damper tech developed for bikes), high-revving four-valve dohc engines, and lightweight aluminum construction (on four wheels the steelversus-aluminum war still rages). Adding turbo control systems fast-acting enough to give a turbo bike smooth corner exits will require serious R&D, whose cost will then be passed on to the consumer, as usual.

Honda had a go at developing a turbo GP bike just after 1980. When the NR500 oval-piston bike failed to cut it in GP racing, Honda’s engineers took a crack at the part of the regulations that permitted a turbo 250 to compete in the 500CC class. Now, 1980 was a long time ago, and a lot has been learned since then. A few relatively crude turbo production bikes tiptoed into the market back then, but their qualities failed to catch on and they were discontinued. The basic problem is that as a turbocharger winds up, twice the rotor speed produces four times the boost. Yes, it takes time for turbos to spool up, but once they do, look out!

I don’t know how far Honda got with its turbo 250, but the word was that power was no problem, 160 hp being obtained from an oval-piston, 16-valve 25OCC twin. That makes perfect sense since various staggering amounts, up to 1,300 hp, have been claimed for the strongest 1.5-liter turbo GP cars of the 1980s (1.5 liters is 6 x 250, and 1,300 divided by 6 is 217 hp). On the other hand, that 25OCC twin, with all its plumbing, heat insulation (somebody has to sit on the thing), and wastegate plus controls, supposedly became pretty big.

But let’s play angel’s advocate and suggest that in the third of a century since then, a few things have been learned. GM’s little Ecotec-four economy-car engine now has its exhaust plumbing cast in the head, with the turbo bolted right to it; can’t get much more compact than that. If serious boost is used, you’d have to find room for a charge cooler (compressing air by turbocharger adds heat to it, which in excess leads to destructive detonation. To prevent this, we cool the compressed air on its way to the engine via a heat exchanger).

BY THE NUMBERS

>150

BOOKS IN MY COLLECTION ON MOTORCYCLES AND MOTORCYCLE ENGINES (I STOPPED COUNTING AT150)

107

BOOKS IN MY COLLECTION ON AIRCRAFT AND AIRCRAFT ENGINES

41

BOOKS IN MY COLLECTION ON RACING CARS AND ENGINES (ALWAYS ON HAND: HANDBOOK OF CHEMISTRY AND PHYSICS AND WERNER HAEFLICER’S FIM MOTOOR RESULTS 1949-2012, FORTHEIR VALUE IN KEEPING IT BETWEEN THE LINES)

Well, I think it could be worth a try just to see how a compact turbo twin would mock up in a motorcycle chassis. Unsupercharged engines need the mild 10-percent boost they get from a tuned airbox, but our hypothetical turbo job wouldn’t need such a box, setting that volume free to be used in another way. It would be fun to lay out components on a bench and then start packing them into a light 600 sportbike chassis. It would be cool if it ended up weighing like a 250 but accelerating like a 1000.

But then, there are so many other things we could be trying.

Not long ago I suggested on the CW website that IC-engine-powered bikes could have all the benefits of an electric bike’s smooth, controlled torque delivery. Leave the IC engine in place, toss the big clutch and gearbox, and slip in an engine-driven generator, sending power to a creamysmooth electric driveline. No shifting, no clutching; just turn the throttle and go. The big problem for electrics is short range, but with an IC engine generating the electricity, that objection goes poof.

More objections: The generator and electric motor are heavy, and they are not 100-percent efficient. Which would be faster, which would get the better mileage? A conventional IC-engine-powered bike with clutch and six speeds?

Or a super-easy-to-control ICelectric bike that held its engine at its most efficient point of operation? Might be fun to find

I THINK IT COULD BE WORTH A TRY JUST TO SEE HOW A COMPACT TURBO TWIN WOULD MOCK UP IN A MOTORCYCLE CHASSIS... IT WOULD BE COOL IF IT ENDED UP WEICHING LIKE A 250 BUT ACCELERATING LIKE A1000.

out. Spare any cash, mister?

Change will come. We just don’t know when or what form it might take. Shall we ignore all the possibilities, dig in our heels, and insist that bikes remain forever what they are at this moment? That has never worked; in proof,

I offer that the first bikes had no throttle, had to be started “in gear” because they were direct drive, and needed “light pedal assistance” to climb anything more than a modest hill. Two speeds and the free-engine clutch were a revolution in 1911; should we have stopped there? Three speeds saw TT racers through the 1920s; does that make nonsense of today’s six speeds? Drop disc brakes and go back to classiclooking but fading drums whose heat expansion loosens the spokes? If motorcycle perfection lies in the past, when exactly was it achieved?