Moto Morini 500 Turbo

The Moto Morini 500 Turbo (prototype),
originally published
in "Bike" magazine, July 1982


"Bolognese Sauce"

Throughout last year (1981) the residents of a quiet Bologna suburb were regularly treated to the sight and sound of a scruffy black Morini V twin growling along their streets to and from nearby dual carriageways. It obviously wasn't just another 500cc prototype - it's motor appeared to breathe through a collection of washing machine parts, the steering head was loaded with dials and controls, and the tester riding it occasionally fiddled with various knobs on a small electronic control box. Had those same residents visited the Milan motorcycle show last November, it’s likely they'd have failed to make any connection between the slickly finished machine grabbing all the attention on the Morini stand and that ratty test bike tooling up and down the Via Alfredo Bergami back home in Bologna.

Except that both bikes had Turbo written on their side panels. Morini, the smallest of the Italian motorcycle manufacturers making it’s own motors, just had to be the least likely candidates for the title of First Non Japanese Production Turbo Makers. Committed to moderate production of a standard range of machines of no more than half litre capacity, using 72^o V twin motors and a single-pot derivative, the little Bologna factory’s philosophy hardly included assaulting the problem-strewn heights of turbocharging - let alone turbocharging a V twin; something supposedly so difficult Honda only did it to show off. Yet the decisions which sent Morini down Turbo road were taken nearly 10 years ago. In 1974, soon after introduction of the 350cc Sport, Moto Morini began looking at what to do next.

Morini were determined to stick with the 72^o motor which had become their trademark but at the same time it was clear that hogging Lambertini's design out to 500cc for the Maestro was pushing its ability to produce horsepower in the required amounts.

In any case, the company whose early 175cc four stroke sportsters gave Agostini a racing start in life harboured a deep rooted antipathy towards what the Italians quaintly term maxi motos. In Morini's view, increasing engine capacity and therefore mass to gain horsepower is a route which quickly runs into the law of diminishing returns; power to weight ratios improve sure enough, but rarely fast enough to match the weight increase, while the hassle of meeting noise and emission regulations is something a small factory can well do without.

They even produced a chart to back up the decision to opt for turbocharging. Claiming to show the general trend in maxi moto design from 1973 to this year (1982), it plots a rise in big bore output from around 70bhp to nearly 100, or a 30 per cent increase. At the same time big bikes have become about 16 per cent heavier as a rule, say Morini. The crunch comes when you do the sums and find power to weight ratios on the biggest multis have only improved by 11 per cent (not to mention the fact that Alfonso Morini would turn in his grave at the thought of a 550lb Morini hitting the streets. Looking at conventional solutions lead the company up blind alleys for three years. Until it considered turbocharging there didn't seem to be any way of making an acceptably fast yet light medium capacity machine without designing a new motor. And re-tooling to do that would have affected the whole range. In 1976 Morini finally decided to go for a turbo, aiming for 750cc performance from their existing 500cc powerplant with similar fuel consumption and little more weight than the standard bike. It was an ambitious project not least because the only turbos available at the time were almost useless on engines smaller than two litres but five years later they had their 500 Turbo. At least it looked as though they had. The pre-production model on show at Milan was strikingly different from any previous Morini, but so well hidden behind the bodywork was the rear of the motor that it really could have had a washing machine in there. Only clue to its internals was an incomprehensible full colour diagram laying bare the baffling complexities of the Moto Morini Turbo System.

Closer investigation was impossible with dozens of Milanese pressing in for a better look and the sensible thing to do seemed to go back to the factory some other time. Which is why I was crawling through Bologna a few months later, nursing a hired Fiat 127 through the traffic and mentally composing a book entitled: "101 Uses For A Dead Heathrow Baggage Handler". Yup, on strike again for an increased Smarties allowance or something.

The Morini factory is a surprisingly small concrete building hemmed in on all sides by apartment blocks. It's small entrance hall holds a display of racing machinery from the '50s and '60s plus examples of the current range of models. Design and admin offices occupy the main body of the building, and rolling road testing, final checking and dispatch are in the basement.

After being introduced to Morini's director Gianni Marchetti, Jim Forrest and I were shown round the works before being ushered into the Holy of Holies, the development workshop. If Honda allows two per cent of its annual budget to R&D, Morini allows about two percent of its space. The workshop was about the size of a Jap R&D department's executive washroom although it was obviously ample for the factory's needs, with a ramp leading down to a dyno room in the basement. The Milan Show turbo was on a bench in the centre of the room, stripped of its bodywork and turbo gear. Resting on the floor was a horrible battered object which was none other than the original prototype - now completely knackered after two years and 110,000 km of road testing round the city. If it hadn't been for Big Four interest in turbocharging, which undoubtedly preceded the introduction of really small turbines, the Morini project might still be waiting in the wings. Last November Morini still hoped to find a home grown item for production turbos but it hasn’t materialised and a Japanese IHI unit similar to those used in the Oriental boosters will sit behind the rear cylinder when the Italian turbo arrives in the showrooms.

Having found their turbocharger, Morini still had a bundle of problems to overcome. The two main ones were getting a turbo system to work adequately given the uneven exhaust pulses of a V twin, particularly at low rpm, and secondly Lambertini and his development engineers Paolo Zaghi and Luciano Negroni had to devise special methods of keeping the cylinders cool

 

while all those hot, compressed gases were being stuffed back into them. Honda, you'll remember, tackled the first of these problems with a complex system of electronic controls, fuel injection and a plenum chamber. Morini's solution was far simpler - simply cut the turbo out of the system at low revs and feed mixture directly from a single 36mm Dellorto carburettor into the inlets. Simple though it sounds in principle, in practise the Morini system calls for a distributor between the turbine and inlets to direct the mixture flow. This was designed and placed at the end of an intercooler between the turbo and the cylinder heads. At low rpm the distributor closes the mouth of the intercooler and mixture flows across it into the motor. Exhaust gases still spin the turbine but the compressor on the other end of the shaft just pumps the same captive charge of air round inside the intercooler. When the revs rise higher than a couple of thousand, sensors measuring depression in the inlet manifold tell the electronic control units it’s time to operate the distributor, which opens the intercooler.

Schematic diagram is Morini’s own, showing the importance of the intercooler

Mixture is diverted down its centre to the compressor, then pushed up the outside to the inlets. To avoid momentary fuel starvation as the air already in the intercooler is stuffed into the motor, a small injector nozzle working on pressure from the head of the fuel in the tank squirts juice into the compressor vanes.

The first prototype featured a fully adjustable distributor control on the steering head which allowed Morini to find the optimum revs for the change from normal to boosted breathing. Once they'd sorted this out, there was still the problem of greatly increased heat to overcome. In faint hope that the Universe still contains any sentient beings not already bored to tears by the theory of turbocharging, I’ll briefly re-iterate the sordid details.

A conventional internal combustion engine is both limited and fairly wasteful. It's limited by the ability of atmospheric pressure to fill its cylinders during the intake cycle, then it just pours about 35 per cent of the energy it produces during combustion away down the exhausts in the form of heat and gas momentum. The function of a turbocharger is to harness some of this wasted energy by making it spin a turbine which in turn spins a compressor which stuffs much more mixture into the pots than atmospheric pressure could manage. The result is, say, a 500cc motor which fills up with as much gas as a 750 or 900 and puts out equivalent power and torque. All you have to do is make sure it breathes properly and doesn't suffer from detonation, seizures, melted plugs or any other penalties of overheating.

 

The answer is that the eight-piece glassfibre fairing/body unit isn't there just to make the Morini Turbo look decorative at garage parties. When Franco Marlenotti at RG Studies was given a design brief for the superstructure, it included a stipulation that the lower section must function as part of the cooling system by directing air over the cylinder heads and boosting bitz.
 

the airintakes	location of the turbo, right above the centrestand; the intercooler above the rear cylinder

So twin scoops were placed either side of the single front downtube; the right one sending air over the front cylinder head, inlet manifold and intercooler and the other sending air over an oil cooler lying almost horizontally in the opening. A vent between the cylinders spills air on to the rear head while foils on the side panels turn a cooling breeze on to the rear barrel.

Yet more scoops on the side panels are supposed to cool the turbo and a large exhaust collector/silencer cradled in a frame extension under the tail. All this hot air exits through a slatted vent on the tail. Aerodynamic considerations also played a part in the fairing design. It's often said that your average, unfaired motorcycle is an aerodynamically perfect as a flying brick. Unfortunately, faired motorcycles are not necessarily much better. Parting the air in front of the machine is less than half the battle because it’s the drag and turbulence around the rear end and in the bike's wake which does most of the damage. As the airflow breaks up over the bike and rider it creates an area of low pressure holding the machine back, soaking up horsepower which ought to be making it go faster.

Morini's half-fairing is nowhere near perfect but they say the Suzuki RG500-style tail and through-flow of air reduce drag, while the blending of fairing and petrol tank at the front gets rid of unwanted turbulence behind the screen which, is where the air intake for the carb is situated. The crucial factor in top speed though is still weight.

There's still one more unique feature on the Morini turbo. A wastegate control. Lambertini was not content with a conventional springloaded wastegate which opens when exhaust pressure reaches a pre-set level and bleeds off the excess, thus limiting turbine speed and so preventing boost rising to dangerous levels. So yet another electromechanical control was added. Taking it’s instruction from pressure in the outlet side of the compressor venturi, the wastegate control lets boost pressure rise to nearly 18psi as the motor spins to 5,500 rpm before operating the wastegate, causing boost pressure to fall rapidly and level off at 12psi when 7,000 rpm is reached. From 2000 engine revolutions, cracking the throttle open spins the turbo to maximum boost in 1 1/2 seconds. Then the controlled opening of the wastegate cuts boost by 30 per cent.

 

system make the Morini as smooth and wellmannered on the road as Honda's computerised fuel injection? A bike which matches the Honda Turbo's smoothness and handling while giving its rider 120 fewer pounds to haul around would certainly be worth all that effort.

If it lives up to the manufacturer’s claims it’ll be at least as fast as the Honda Turbo at 210-215kph (130-133mph) flat out and purportedly infinitely less thirsty at 55mpg overall going up to 60mpg at steady round-town speeds. According to Negroni there's little noticeable ‘turbo lag’ because the intercooler distributor switch allows a head of pressure to build up and come in with a bang when it goes over to boost. When I was in Milan last year, however, Paolo Zaghi said the switch operated at 4,000rpm. If that's correct then you’d expect the motor to be struggling a little as the 8.6:1 compression pistons (as opposed to 11.2: 1 in the standard mill) sucked mixture through the single carb, long inlet manifold and round the sharp bends into the Heron heads.

Yet Morini's dyno charts claim a 10 per cent increase over power at four grand . . . some mistake here, surely. Or maybe it's my total ignorance of Italian. Most of the scepticism which has greeted the turbo stems from the few changes Morini have made to the 500's internals. It runs a stock crank but the low compression pistons are forged. Only other change specifically related to turbocharging is a beefed-up version of the two-plate dry clutch, though the factory has finally broken with tradition and linked the gear selector to a left foot lever. A sixth ratio has been added to the gearbox as well - both these mods appearing on the latest export versions of the 500 (the 500Sei).

To be fair turbocharging doesn't increase mechanical loads on the bottom half of the motor, in fact the softer compression reduces the hammering, though the whole transmission has to relay far more power to the rear wheel. Nor does moving the power peak 1000rpm higher come near the very high revs which racing Morini big ends were asked (but failed) to cope with in the Island some years back. Those forged pistons are there because thermal loads on the top half of the motor are so much higher than in a conventional motor and it's this problem of cooling which is more likely to cause failures than mechanical stresses.

But Gianni Marchetti doesn't see arrival on the booster scene as having anything to do with muscle-flexing or joining the tailchase Honda started with their turbo. Morini has been at pains to point out that it started developing it’s turbo in 1976 and it’s possible that if the company had had the clout to persuade a European manufacturer to develop a suitably small turbocharger a few years ago it might have had the world's first production turbocharged motorcycle in the shops.

The Bologna factory decided long ago that there was sufficient demand for 120mph-plus machines to make it worth developing one of their own. Alongside the turbo, Lambertini drew up designs for a 650cc Maestro (the Misstro?) and experimented with different head designs - conceivably we might have been offered something like a 72^o version of the Ducati Pantah - but those designs are still on the shelf. Look at it another way. Morini has neither the desire nor the resources to make large, heavy machines. In Marchetti's view, the cash spent on meeting increasingly restrictive noise and emission regulations, on the back-room political infighting leading up their introduction and promotion in the dwindling marketplace would be good money thrown after bad. Or: there's no way 116 Italians can beat Hondawayamzuki.

If and when a few Morini turbos are delivered into the hands of the press for evaluation it'll be clear once and for all how well the factory played its cards. Until then the cynics will continue to claim Morini is merely making a virtue out of a necessity, while more charitable individuals will no doubt reach for their paperback copies of Small Is Beautiful.

Talking of small, Morini decided several years ago that it needed to move out of the moped market. Now it’s not so sure. One project which is nearly ready to go should the moment arise is a 50cc four-stroke motor. It'd be one hell of a follow-up to a 130mph turbo.

 

presently also published by the British Morini Riders Club