If ever an engine was made for turbo-charging, the GSXR750 was it. Ultra reliable, proven in all forms of motorcycle competition worldwide since its launch in 1985, the Gixer loves being thrashed in a way that Elvis was keen on bacon sandwiches.
With a 160bhp claimed output, you will need the steering damper and beefier clutch supplied as part of the American made, Moisan GSXR750 turbo kit. Oh yeah, a clean change of underwear might be advisable too..
From the rate at which the pick-up truck way ahead was being reeled in, I knew the GSX-R was moving mighty fast, but even so it was a shock to glance down and find the speedo reading 180mph with more to come. Sheeesh! I´d realised the Suzuki was powerful, but I’d only been holding the throttle wide open for a few seconds and you just don´t expect such speed from a stock-looking GSX-R750.
The reason was obvious from the small white-faced boost gauge next to the speedo. Along with the Turbo stickers on the fairing, it showed that this was no ordinary GSX-R. It´s the latest turbo-nutter-bastard bike from Florida-based American Turbo Systems, and it has the potential to make over 180bhp.
Such a serious kick up the arse from the GSX-R was long overdue. For anyone addicted to the current GSX-R750´s trademark blend of revs, agility and attitude, it has long been a mystery why Suzuki has not repeated its successful mid-Eighties trick by following-up the 750 with an equally focused and heavier-hitting 1100cc model. The GSX-R is a storming bike, but it simply doesn´t have the power to trade four-cylinder blows with the FireBlade, ZX-9R and YZF-R1.
Unless, that is, there´s a horseshoe hidden inside its boxing glove. American Turbo Systems boss Mark Moisan, whose mindblowing old-style GSX-R1100 turbo special produced over 420bhp and was timed at 229mph, has developed a kit to give owners of the watercooled GSX-R750 some extra punch. If you combine the 750´s ace chassis with a motor pumped up by forced induction, his theory goes, the blue-and-white corner has a genuine contender at last.
This kit differs from the first one Moisan produced for sale, a 200bhp package for Honda´s Super Blackbird by using a Schwitzer turbocharger in place of the CBR´s Aerocharger variable-vane unit. ’The Schwitzer works very well and it´s even smaller than the Aerocharger, which is important because the 750 is so compact,’ he says. ’It´s a conventional turbocharger, more like the Rayjay I used on the GSX-R1100, but a much newer and more efficient design.’
The Schwitzer is rated at 275cfm (cubic feet per minute), enough to lift the GSX-R750´s peak output to over 180bhp with the maximum 0.55bar (8psi) of boost. But Moisan says that´s just too mental for street use. The kit´s standard setting will be 0.4bar (5.8psi), good for 150-160bhp on pump petrol. ’The kit will include a switch that will give a choice between 5.8 and 8psi,’ Moisan says. ’On the higher setting the bike is totally unrideable, but that´s what some people want…’
The kit, which costs $4995 (just under three grand), will come complete with turbocharger, intercooler, boost gauge, and a stainless steel exhaust system with carbon end can. As well as all necessary fitting brackets, it will also include jets to modify the Suzuki´s 39mm Mikuni carbs. (Moisan is also working to adapt the kit for this year´s injected GSX-R, and should have it ready soon.)
Another important component of the kit will be a 1mm thicker base gasket, necessary to reduce the GSX-R´s compression ratio from the standard 11.8:1 to a detonation-preventing 10.5:1. The resultant top-end stripdown inevitably pushes the kit´s installation time well above the six hours estimated for the Blackbird kit (which leaves the motor untouched), but rather that than a holed piston. Given his experience with the remarkably standard bottom-end of his monster GSX-R11, Moisan is confident that the 750 motor will be strong enough.
Despite the GSX-R´s compact nature the turbo and its assorted parts tuck away so efficiently that nobody glancing at the bike would suspect that it had anything naughty up its skirt. Even when you climb aboard and fire it up, the Suzuki feels deceptively ordinary. Moisan hadn´t fitted this bike with the switch to vary boost, and it was on the lower of the two settings, at which its 16-valve motor idled impeccably and was as docile as a stocker at low revs.
At town speeds only this bike´s heavier clutch, due to a stiffer Barnett spring, hinted that there was serious horsepower waiting to be unleashed. Moisan had fitted the stiffer spring to be sure the clutch wouldn´t slip during my test, but has yet to finalise the mod that will be included with the kit. He thinks that using an extra Suzuki spring will give sufficient strength with a lighter feel.
Any pretence that this was a normal GSX-R vanished very rapidly when the revs rose and the bike began responding to a tweak of throttle with greatly increased enthusiasm. At this low boost setting the dreaded turbo lag could barely be felt at all, though that´s not to say that throttle response was always good. When I cracked the throttle open at 4000rpm in top with no boost showing, the bike accelerated cleanly but feebly, much as the stock Suzuki would have done.
If the turbo-bike felt pretty unspectacular at low revs, above six grand it was in a different league to every other GSX-R750 I´ve ridden. Tweaking the lever in third gear with some boost showing on the dial resulted in barely a pause: the front wheel went light and the bike belted towards the horizon while my left boot tried to keep up. The turbocharger made a familiar fluttering sound each time I backed off to flick through the gearbox, and the bike kept on stormin´ from three-figure speeds with neck-snapping force.
When I glanced down at an indicated 180mph the bike was still pulling slightly, with boost maxed out at 0.4bar. There was a bit more speed to come given more room, but I wasn´t gonna find it because at those velocities the apparently near-deserted Daytona road had suddenly started resembling a High Street full of very slow-moving Harleys and trucks.
The turbo´s extra power was a hoot at lower speeds, too, adding to the entertainment every time a flick of the wrist in second gear sent the front wheel arcing skywards. Doing the same thing in first would have resulted in an instant back-flip. But unlike some ultra-short and light turbo bikes, which can be right vicious animals, the GSX-R came on boost quickly and progressively enough to make it quite controllable.
Predictably there were no problems with the handling, which benefited from the added stability provided by the transverse-mounted steering damper (a must with this much poke) and was otherwise standard. That twin-beam GSX-R frame is rigid, and the suspension, brakes and tyres are well capable of handling the extra power.
So it´s f-flippin´ fast and it runs very sweetly, this turbo GSX-R750, at least at this relatively restrained level of boost. It would have been interesting to have ridden the thing on the higher setting, just to see how scary it really was, but that wasn´t practical at Daytona and anyway Moisan was adamant that the Suzuki is a lot more fun with the boost at a level that allows such a crisp, rapid throttle response combined with good manners at slower speeds.
Besides, just how much horsepower do you need? Moisan put the bike on his dyno immediately after my test, and at 0.4bar it produced no less than 164.8bhp (approx 50bhp up on stock). When you consider that Jamie Whitham and Peter Goddard´s factory GSX-R750 Superbikes make a near-identical estimated 165bhp at the crank and have been timed at 189mph, it kind of puts that sort of performance into perspective.
Get Suzuki motorbike insurance for the suzuki gsxr750 turbo.
Engine Liquid cooled four cylinder, four stroke
Claimed power (bhp) 160bhp
Compression ratio n/a
Transmission Six speed
Twin spar aluminium alloy frame
Front suspension 43mm telescopic, adjustable
Rear suspension Monoshock, adjustment for preload and rebound damping
Font brake four-piston calipers, twin 320mm discs
Rear brake single 282mm disc
Top speed 180 mph
Fuel capacity 17 litres
Current price $4995 for turbo kit (this will invalidate your warranty)