Bimota YB4750IE SP

Bimota YB4750IE SP
Manufacturer	Bimota
Production	15 units
Engine	Four stroke, transverse four cylinder, DOHC, 5 valves per cylinder.
Compression ratio	11.2:1
Ignition	CDI
Transmission	6 Speed
Frame	Two diagonal beams in section bar made of aluminum with internal ribbing. The cylinders are supported by plates bolted to the beams and the swing arm is made of aluminum
Suspension	Front: 42mm Gas telescopic forks, external adjustment for anti-dive Rear: Gas single shock, external adjustment
Brakes	Front: 2x 320mm discs Rear: Single 230mm disc
Front Tire	3.50-17
Rear Tire	5.50-17
Weight	180 kg / 396.8 lbs. (dry),
Fuel Capacity	20 Liters / 5.3 US gal
Manuals	Service Manual

Engine

The engine was a Liquid cooled cooled Four stroke, transverse four cylinder, DOHC, 5 valves per cylinder.. The engine featured a 11.2:1 compression ratio.

Chassis

It came with a 3.50-17 front tire and a 5.50-17 rear tire. Stopping was achieved via 2x 320mm discs in the front and a Single 230mm disc in the rear. The front suspension was a 42mm Gas telescopic forks, external adjustment for anti-dive while the rear was equipped with a Gas single shock, external adjustment. The YB4750IE SP was fitted with a 20 Liters / 5.3 US gal fuel tank. The bike weighed just 180 kg / 396.8 lbs..

Photos

Overview

Bimota YB4ie SP

The SP version was a special series of the YB4 EI. It was built specifically for Sport Production Championship races. There are some things that can only happen in Italy and this I ventured through another mouthful of Virgionio's enormous "b" for Bimota shaped 35 Th. birthday cake; was definitely one of them. Europe's press had assembled in the Roman sunshine to ride Bimota's F1 World Championship winning YB4 and I'd managed barely half a dozen laps of the bumpy Vallelunga circuit before two of the three Yamaha engined bikes present had been put out of action. At this point we'd stopped for a long, late arriving lunch after which Signor Ferrari, designer shades for once removed from beneath his mop of black ringlets, had stepped forward to cut his cake - the cue for the assembled Bimota personnel to pop corks and start a champagne spraying session that soaked the bikes, press and especially themselves. The remaining few glasses of bubbly having been shared out, the mechanics who'd spent the year helping Bimota to their first four stroke World title striped off their overalls and amid gales of laughter, stepped into Ferrari's and team mate Davide Tardozzi's leathers before firing up the remaining YB4 and a Ducati engined DB1 and roaring off for a few laps of the track. The party moved to the pit lane, where Ferrari appeared with a pair of stopwatches and proceeded to make rude gestures every time the riders came past. Waiting hopefully in my leathers for another ride, sweating from the unfamiliar late October heat and the knowledge that we'd so far shot about a quarter of a roll of film, I didn't know whether to laugh or cry. But you have to hand it to Bimota, they know how to make brilliant motorcycles and they know how to win races and when they have won they know how to celebrate. The year 1987 has brought much to be happy about for the little Rimini firm and it 32 employees. In serious financial trouble so recently, before being rescued by the sales of the magnificently styled DB1, not only have they beaten the mighty Honda to the F1 Championship this year, they have also won the Italian F1, Superbike and Battle of the Twins series, not to mention the home round of the World Endurance round at Monza. Now at the seasons end, they are poised to begin production of a line of 750 & 1000 cc Yamaha engined machines that should ensure even greater prosperity in 1988. They'll soon start building the first of 300 FZR 1000-powered Yb6's. Sales manager Davide Genghini said and they plan to make 200 YB4's perhaps half on which will be for racing. Give or take lights and a silencer they'll all look the same (although the YB6 might have a different color scheme). The fairing is curvaceous and immaculately finished with air scoops, a small oil cooler and a big radiator at it's front. The frame is a massively thick, rectangular section aluminum beams running diagonally down the bike to suspend the angled forward 20 valve engine, the one piece tank and seat unit has absolutely no room for a pillion. The chunky 42mm forks hold four pots Brembo callipers, huge 320 mm discs and Michelin shod 17-inch wheels almost wide enough to make a side stand redundant. Ogling the styling and craftsmanship of the YB4 is one thing, sitting on it is another, when you are distinctly UN Italian 6' 4 in height, is something else again. Already that morning I'd been out to learn the circuit on a race prepped DB1 but had reluctantly come in after a few laps because, as well as probably the most beautiful exhaust note I've ever heard, the Ducati engined bike had a riding position so cramped that I could barely get my feet on the footrests at all, let alone change gear properly. I'd then watched my YB4 pull in to the pit lane, listen to it's smooth four cylinder cry die as the engine stopped, and persuaded a mechanic to remove a bit of padding from the seat back. And yet the Bimota felt so tiny that after throwing a leg over the seat I still had to look down to check that this was the YB4 I was astride, rather than another DB1. The screen is small and flat, the seat is low and set so far forward that even with less padding than normal I'd still need six inches chopping out of the tail hump before I'd fit properly. At a standstill the bike felt very light, despite the unconnected starter motor that had been added to bring it's weight above the 65 kg (363lbs) minimum weight limit for the day be fore's Superbike race. With a Kevlar fairing rather than the glass fibre the Bimota can slim down to 155 kgs for Formula One. Visor down, gear lever up into first, take a few steps and dump the clutch. The YB4 pulled cleanly away down the pit road and out onto the circuit, the FZ engine seemingly having lost little of it's notorious flexibility with the addition of a factory race kit. Vallelunga's first bend is a blind chicane; don't brake till you've seen it at racing speed and you'll take the direct route through the dirt, for sure. At well below racing speed I saw the chicane, grabbed a fistful of Brembo's and the Bimota slowed with startling sharpness. I opened the throttle again, accelerated into the chicane flicked right left right and headed towards the next bend with a new found respect for the brakes. The Vallelunga track's a bit Miguelo Mouse, to say the least. It's a big oval with sweeping banked curves at each end, a chicane added as an after thought to break up each straight and an infield section so bumpy it looks like the local gas company had been using it for pipe laying rehearsals. The first banked sweeper was most fun, down a couple of gears, tip the Bimota right with barely a touch of the bars and power round, up the banking a little an then back around for the second apex before barrelling up the straight with a flick flick flick through the close ratio gearbox. From the 11 grand redline the revs dropped barely to 10; the bike kept surging forward on an enormous wave of power. The YB4 can be cornered with the precision of a surgeon's sharpest scalpel although like the blade it will draw blood in the wrong place if not used with the necessary competence. Every rider movement is translated directly into action, brush the brake lever and the bike slows, nudge the bars and it changes direction, touch the throttle and the tacho heads for the red. The steering felt especially light and instantaneous in response, Suspension comprises special lightweight Bimota built forks using Marzocchi internals (production version will be all Marzocchi) and a vertically mounted Marzocchi shock, and was firm enough to give instant feedback while remaining soft enough to take the circuits worst bumps in its stride. But responding to every rider input also means reacting to every mistake. One lap I touched the front brake to close to the apex of the infield and the bike stood up, almost stopped and made me resolve not to be so clumsy again, though the Michelins did not let go. Hard braking would get the rear wheel hopping off the ground but the front end stayed planted, stable and always under control. Opening the throttle requires even less pressure than the brake lever. Bimota used Yamaha's race kit CV carbs for most of the season, preferring to make use of their superior fuel consumption rather than gamble with the magnesium bodied factory slide carbs they were offered by Yamaha .On the track you barely drop the revs low enough to use the mid range power but the bike drove out of crisply and hard all the same and sometimes to hard. At the first gear hairpin it was too easy to jerk the throttle and send the bike running wide across the track. Especially when you were so bent double that you were tempted to sit on the rear seat hump. The YB6 roadster will run a stock FZR litre engine and CV induction system but both road and track YB4's will use Weber fuel injection. Bimota have been developing the system since May but had first raced with it only on the day before - Tardozzi piping Marco Luchinello on the eight valve Ducati to come third behind winner Fred Merkel (Honda VFR) and Ferrari (on a CV Carbed YB4) in a Vallelunga Superbike race. Virginio's Championship winning engines were little more than the sort of race kitted FZ lumps you or I could put together given the necessary five-figured sum. Bimota had to buy them, too, Frederico Martini, the firms, large, bearded technical director, estimated that rear wheel power was about 108 bhp (presumably on a schenck type dyno, on which a stock FZ makes about 90 bhp, and not the more generous Bosch machine which we use for road test bikes), which is not a lot when you are up against the heavy horses of the factory teams. But Martini thinks that next season, when they are fully developed the fuel injection system Bimota too could be getting 120 bhp plus from the FZ engine. "Our main reason for turning to fuel injection originally was that it can be developed to run correctly at every engine speed, so you can combine good performance with low emissions for road machines. Possibly it will be the only way to meet emission regulations in the future" he said "but we also think our links with Weber will be of an advantage in our racing. This year we had to develop our frame and had no time for the engine, for next season we hope to develop the engine also. "The bike with fuel injection raced by Tardozzi was built only one week ago and is already as good as the YB4 with carbs. I thin we can make up to 25 bhp more with fuel injection - at least 120 or 125 bhp in total. It is difficult to explain why but when using the fuel injection we can develop the engine around it - perhaps using different cams, exhausts, directing more air in other word making the engine run better. One disadvantage of fuel injection is the cost - Martini estimates that it may add on ten percent to the price of a bike and it looks as if new importers Mitsui will have to charge around £15000, that is twice the price of an RC30 - for both models .The first bikes should be available in January and they'll be sold through a network of a half a dozen selected Yamaha dealers presumably alongside the Honda powered HB3 that the Italian firm will continue to produce. Bimota's links with Yamaha are strong it seems, but not too strong. But enough of this crass talk about money. The Bimota YB4 should be discussed for its style, speed, and its beauty. For the sublime way it flicked through the bumpy left right behind the Vallelunga pits before shooting off towards the last bend on the first lap of my second session aboard. For the way it stood on its nose as the powerful Brembo's bit, the exhaust note barked once, twice and the sleek machine banked serenely into the long, final right hander, my knee brushing the tarmac as the corner unwound before my eyes. But suddenly the track was full of waving, jumping Italians and I was swerving and sitting up and braking and using all the amazing maneuverability and braking power to miss them. An American had crashed on the exit of the bend. When they cleared up they decided it was time for lunch. Federico Martini was not at all happy but before long he was smiling again and the champagne was flowing. It had, after all, been a very good year for Bimota. The YB4 had made sure of that. Source Bike magazine December 1987

Make Model	Bimota YB4 EI SP
Year	1988
Production	15 units
Engine Type	Four stroke, transverse four cylinder, DOHC, 5 valves per cylinder.
Displacement	749 cc / 45.7 cub. in.
Bore X Stroke	68 x 51.6 mm
Compression	11.2:1
Cooling System	Liquid cooled
Induction	Weber Marelli electronic fuel injection
Ignition	CDI
Starting	Electric
Max Power	89 KW / 121 hp @ 10500rpm
Max Power Rear Tire	72.7 kW / 97.5 hp @ 10400 rpm
Max Torque	88.3 Nm / 9.0kgf-m / 65.1 lb-ft.@ 8500rpm
Transmission	6 Speed
Final Drive	Chain
Frame	Two diagonal beams in section bar made of aluminum with internal ribbing. The cylinders are supported by plates bolted to the beams and the swing arm is made of aluminum
Front Suspension	42mm Gas telescopic forks, external adjustment for anti-dive
Rear Suspension	Gas single shock, external adjustment
Front Brakes	2x 320mm discs
Rear Brakes	Single 230mm disc
Front Tire	3.50-17
Rear Tire	5.50-17
Dry Weight	180 kg / 396.8 lbs.
Fuel Capacity	20 Liters / 5.3 US gal
Consumption Average	6.5 l/100km / 36.2 mpg
Braking 60 - 0 / 100 - 0	13.2 m / 36.0 m 43.3 ft / 118.1 ft.
Standing ¼ Mile	10.8 sec / 201.8 km/h / 125.4 mph
Road Test	Motosprint Group Test Moto.Journal Moto.Revue In.Moto YB4 vs RC30 BIKE Motorrad Motorrad YB4 vs FZR750R