Bimota YB9 SRI

Given the success of the SR series, development began on the subsequent SRI model with fuel injection in place of carburettors. It was essentially the same bike as the SR and can only be distinguished by small details. They are carbon fibre air intakes, racing screen and a parking light. The fairing now breaks down into three pieces for easier dismantling. The Bimota YB9SRi was launched in 1996 to replace the carburetted YB9SR. The SRi was unique at the time, because it was the only 600cc fuel-injected bike available, and remained so until Triumph's TT600 appeared in 2000. The SRi design was typical of Bimota's efforts at the time. The Rimini-based firm bought FZR600R and Thundercat engines from Yamaha, then installed them in the firm's own custom-built supersports chassis. A racing aluminum frame was festooned with the highest-quality chassis components available, and the engine fitted with Bimota's own intake and exhaust systems. The result was an exotic sports machine, at its best on the track, but also finished to a very high, if occasionally inconsistent, standard.

Source Injected Aggressor, from RPM magazine, March 1996 by Alan Cathcart

It was only a matter of time before the modern era of engine management systems and electronic fuel injection arrived in the 600 supersport arena, and equally inevitable that it would be Bimota that ushered it in - just as the did a decade ago in the Superbike class.

By launching the latest version of their four cylinder 600 sports bike, the YB9sri now entering production equipped with their own EFI developed in conjunction with TDD, as well as with the uprated YZF600R Yamaha engine from the new Thundercat, Bimota have raised the stakes not just in the showroom bit also out on the race-track, both in the Supersport 600 category and the GP world's spin off Thunder bikes class.
Yet in doing so Bimota have also produced a road legal homologation special that is actually far more user friendly on the street than the carbureted bike it replaces, thanks to the responsive pick up from the EFI, combined with the extra power it delivers all the way through the rev range.

Based on a days ride through the Marche hill country behind Bimota's Rimini base on the first YB9sri off of the production line, I'd say the 600 street class has a new benchmark - albeit at the premium price commanded by the Bimota name.
A hand built limited edition, hard noised race replica with the extra sophistication of EFI the Yb9sri sells in its Italian home market for 25,700,000 lira (£10,700) compared to the carbureted YB9 sister at 22,600,000 Lira (£9,400) - or a Yamaha Thundercat at not much more than half that. Superbike prices for a tricked out supersport.
Still, for sure a large production of the first batch of 250 fuel injected Bimota 600's currently being built will end up on the race tracks of the world, especially to challenge the dominance of the Ducati 748sp at European Championship level, where the Desmo Vee Twins made full use if the combined capacity and weight advantages accorded to them under the rules in effect last season.

But in 1996, with the minimum 170kg weight limit the same for all bikes, the Ducati's will not be having it so easy - and of course Thunder bike racing only permits 600cc fours anyway.
That being the case, Bimota's newly signed Australian works rider Fred Bayens - fourth in the 1995 Thunder bike series and second in the 1994 European Supersports Championship - must have a great chance of earning Bimota the GP circus four stroke crown this season. And after defeating the works Ducati team to win the 1995 Italian 600 title against all the odds on the factory Bimota YB9 carbie, Michele Malatesta and team mate Miki Gallina (son of former 500cc team manager Roberto) are bound to be serious contenders for the European Supersports title with their new fuel injected YB9sri Bimota's. Junior superbike racing? Sounds like it. Concocting the YB9sri has entailed much more than simply plugging in a Thundercat engine to replace the old FZR600 motor, and waving a magic wand over it to add fuel injection. However whilst retaining the same basic format as the previous 62x49.6mm FZR design (chassis pick ups are the same as before, for example, unlike on the YZF1000 Thunderace, and the engine castings unchanged).

The Cat engine used forged pistons instead of cast ones for improved reliability at high revs, and for the same reason has an all new crankshaft made of improved material to cure the high rpm crank failures suffered by some Yamaha Supersport teams at 13,000rpm or more in the past couple of years. The new crank also has lighter, smaller webs for improved engine acceleration, which is helped too by a smaller ignition rotor. The result delivers 100.5bhp at the crank, at 11,500rpm on the Yamaha Thundercat, fitted with 36mm carbs - whereas without any mechanical changes (same crankshaft, same 12:1 compression ratio etc.) the same engine delivers 106bhp at the crank in the Bimota guise, running a grand higher at 12,500rpm and translating to 78bhp at the rear wheel. The difference comes from the TDD/Bimota fuel injection package, with four 44mm throttle bodies, a single injector per cylinder, and a high pressure Bosch fuel pump running at 3 bar, all controlled by the ECU mounted on the rear subframe beneath the seat, via a total of five sensors, monitoring coolant temperature, ambient air temperature, air pressure, throttle position and RPM.

Six percent more power at the top end is a hefty improvement that alone would justify fitting EFI - but the benefits are all the way through the rev range.

There is 51-rear wheel bhp from the injected motor at just 8,000rpm, compared to 47bhp in the same day dyno testing from a carbie engine, with corresponding improvements in torque from 56.2Nm to 60.1Nm at the same revs. This translates to noticeably improved mid range pick up when you ride the bike - the kind that made me want to compare dyno sheets when I got back to base. Add in the better response coming off a closed or partially opened throttle, and the benefits of the EFI start to justify its increased cost - especially as the YB9sri does not have the same all or nothing delivery as the previous four cylinder homologation special fitted with TDD/Bimota fuel injection, the flawed Suzuki engined SB7.
The YB9sri's twin spar chassis, made from Anticordal aircraft alloy, has the same basic design as the previous carbie's bike, but now has a cast rear frame brace in front of the back wheel, to which the similarly cast rear upright incorporating the swing arm pivot is welded.

This makes an even more rigid structure to cope with the extra grip delivered by the new generation Supersport race tyres, which ever more closely resemble slicks with a nominal tread pattern moulded into them.
Those fitted to the street YB9sri as standard are Michelin Hi-Sports - though fats Fred (Bayens) will use Pirelli's for T Bike racing - mounted on new, very distinctive cast alloy wheels made to Bimota's design by the same company who manufacture the wheels fitted to Ferrari and Porsche sports cars. The weigh exactly the same as the Marchesini's used by Bimota before, but the rear is actually bigger, at 5.5 instead of 5.0 on the carbie YB9, with the swing arm widened slightly to accommodate it.

This allows Bimota to fit a hunky 180/55ZR17 rear tyre instead of a 160/55, still combined with a 120/70 front on a 3.5 wheel as before. What was this about junior Superbikes? Though chassis geometry is otherwise unchanged, the 1410 wheelbase and 24-degree head angle with just 95mm of trail make the YB9sri feel even more like a four stroke 250GP bike than ever before. The reason is a combination of the rear ride height setting on the bike as I rode it, and the closely coupled riding position, with the narrow distinctive styled bodywork (now with a three way split for improved access) and its trademark Vee neck Bimota screen.

 The test bike had just returned from the Magioe circuit, where the factory development team had set up its handling for optimum racetrack mode, with a 7mm longer rear shock setting, translating to a substantially increased rear ride height, compared to street guise. This gives adequate clearance at racing speeds with the extra grip from the fatter rear tyre (especially for the freer flowing Bimota exhaust which contributes to the 6% power increase), but at the cost of making the chain rub hard on the swing arm on the over run, producing an irritating noise as well presumably undue wear. It also delivers a radical riding position that is more 250GP than Supersport 600, with a lot of your body weight on your arms and shoulders, thanks to the low set clip ons which are steeply raked. This makes the YB9sri as tiring to ride for any length of time on the street as Max Biaggi's 250 Aprilia is on the track, making each 150 mile thankful from the 20 litre tank a physical challenge of endurance!

A two hour stint of coping with switch back mountain roads left me rueing the Max factor with sore wrists, exacerbated by the outstanding braking delivered by the Brembo 320mm front discs another powerful weapon in the bikes armoury for Supersport racing. Though more cost effective steel rotors rather than the more expensive cast iron discs used on the Brembo equipped Superbikes, these are a big improvement over similar budget Brembo's I have used recently, with noticeable improved bite, matched with lots of sensitivity that allows you to stroke off a lot of excess speed, or alternatively to squeeze hard and get the back wheel waving in the air. And it does, thanks to an increased front end bias with the higher rear ride height setting. But the YB9sri mounted street squirrels will need to bullwork their body into beefcake Bayens mode to prevent the Max factor taking its toll - either that , or drop the rear ride height a tadge, and go for longer chain life as well.

But set up as it was for the track (and the suspension linkage is fully adjustable, so you can tailor the bike for individual tastes) the Bimota's steering was flawless. You have just got to think about changing directions and the bike does it - yet without being twitchy or nervous, and without any straight-line wobbles over rough surfaces, as bikes with radical race ready geometry have been known to do. It also does not tuck the front wheel under on tight mountain turns, even trail braking into the apex, and a key factor in this is the surprising quality of the Paioli forks.
Lets face it until very recently, Paioli suspension was budget class second best stuff you only used if the price was right. But now they have moved their development and manufacturing quality up several gears, And Bimota's customers are the immediate beneficiaries. The 43mm forks on the YB9sri are set up pretty stiff, so there is not a lot of front end dive under the hard braking those Brembo's are capable of - but the surprising thing is that they did not chatter the front wheel even when in the cool winter sunshine, and handled the broken asphalt of the frost ravaged Marche road really well, ride quality is truly exceptional for such a short wheelbase bike weighing just 175kg dry.

The Paoli rear shock - fully adjustable fro pre load, compression and rebound, whereas the forks come only with rebound adjustment as standard - compression is available as an option - also coped well with the changes in road surface and handled a series of whoop-de-doops that have caught out other bikes I have tested over them, with aplomb. You can actually feel the progressive response of the Bimota linkage at work as you rise and fall over a series of bumps that any Irish road race would be proud of - but the same shock setting combines with the fatter 180/55 rear tyre to give excellent Final Final Final Drive out of turns, at the expense of only a little under steer compared to the narrower 160/55 tyre fitted to the carbureted YB9. And the bigger tyre definitely did not affect the steering in the form the bike was set up in - it still flip flops effortlessly through a series of curves like an Aermacchi fighter aircraft on autopilot, with embarrassing little rider effort to make it switch direction.

This is a really well balanced and nimble four cylinder four stroke, with poised yet responsive handling the equal of the Ducati 748 - and I know of no better compliment in street bike terms. In "Iniezone Elettronica" guise the YB9sri will be available mainly in the red of the test bike (yellow continues as an option) which considering it is exactly the same shade of Italian racing red as a Ducati 916 Superbike is a bit of an irony - but then Bimota's biggest Supersports rivals are just 100km up the road in Bologna pinched the YB9's trade mark yellow livery for the 748 Desmo, so maybe they are just repaying the compliment.

Finish is good, as you have a right to expect at Bimota price levels, but the fact that the custom made instrument dash is offset to the left (presumably to make the all important rev counter more visible) looks plain tacky, worthy of a special builder, and should be redressed pronto. I would also expect to see a digital temperature gauge on a bike like this, and a little more padding on that "Road Racer" rear seat would be welcome- though maybe its board like quality is all part of the Max factor? Footrest position is great, and the gearchange outstanding, smooth and slick with clutch less upward gear changes a cinch. But the EFI did not seem to have a choke program in it, so that firing up the Bimota after a photo session at Riccione promenade in barely double-digit winter weather left it constantly stalling until the temp needle crept out of the blue. Solution? Pretend you are fast Fred and blip the throttle to warm the motor in best paddock posing mode. Still in the natural absence of a choke knob like the carbie YB9 has in the middle of its fork stem, the EFI needs to be reprogrammed to compensate.

But once you do get the Bimota's Thundercat engine hot to trot, it will convince you of the benefits of EFI, with a seamless spread of power delivered in hyper smooth manner. The YB9sri pulls cleanly from just 2000rpm - even when you gas it wide open this low down, it does not splutter or snatch, just build revs, slowly at first, then with noticeably faster pick up from 5300rpm upwards. Then at 7500rpm, engine speed really quickens, with a rush of revs up to the 13000rpm redline that is not fierce enough to unhook the back wheel even cranked over on coldish tyres. The YB9sri really motors up high, but it cranks out the power smoothly as well as smartly.

The EFI delivers the instant response of a set of flatslides, with out their abruptness. Best of both worlds, really - and well worth the entrance fee to the Bimota owners club.
But it is not just in comparison to its carbureted counterparts in the Supersport paddock that the new Bimota has an edge. Well made, with no squeaks or rattles from the three piece bodywork even on this hard used development bike, it is definitely a more sophisticated and well rounded bike than the firstYB9 I rode two years ago. The improved chassis specification delivers better braking, more tyre and uprated suspension. Taut and tight feeling, the YB9sri has the responsiveness of a superbike coupled with the nimbleness of a GP racer, packaged for the street with the allure that only Bimota can deliver to the four cylinder sportsbike scene. It provides the new standard for others to aim at in the Supersport 600 class, on road and track alike Fast Fred's a lucky Ocker!

Source Injected Aggressor, from RPM magazine, March 1996 by Alan Cathcart