Tweaked: 200hp Turbocharged Kawasaki Z900RS Cafe

Is this the ultimate Zed? With 200hp and over 100ft-lbs in a package you could daily ride, we reckon it could well be... Test: Alan Dowds Photography: John Goodman

Kawasaki’s slick Z900 RS Café is a great looking retro – but the motor can feel a little on the soft side. Over in the UK, top drag tuning shop Big CC Racing has fixed all that though, with a power-doubling turbocharger install – that costs just $9,000 AUD…

Who doesn’t love the idea of a ‘street sleeper’? A bog-stock bike that seems like nothing special, just sitting at the red light. Waiting. Waiting for some show-off to pull up on his full-bore superbike, or fancy German sports car. Then, when the lights turn green, the plain-Jane machine pulls out an ace in the hole, blasting away from the flash kid like he’s stuck in neutral.

Back in the day you might have had a tuned big-bore motor hidden inside an otherwise-standard bike – or a superbike motor crammed into a lightweight chassis. A GSX-R1100-powered GSX-R750, or a FireBlade engine inside a CBR600 (or 400!) frame.

But nowadays, with stock litre superbikes weighing so little and handling so well, there’s little point in that sort of build, and the true street sleeper has become a rare beastie.

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So thank the Lord for guys like Sean Mills at Big CC Racing in Wokingham, England. Sean’s been at the heart of the ultimate horsepower tuning scene for nearly three decades, and his bread-and-butter work is megabucks 500bhp turbocharged Hayabusas, aimed at drag racers and outright speed record merchants. His magnum opus is dubbed ‘Project Pisstake’ – a turbo Hayabusa motor that puts out 1000bhp… You might remember him from our features in Rapid Bikes back in the day.

He’s no one-trick pony though, and likes to come up with something different now and again. Like this: a Kawasaki Z900 RS Café, with a simple bolt-on turbo kit that uses the stock engine internals, modest fuelling changes and a low-boost tune. The result, as Sean is keen to show me on the dyno before I take her for a spin, is a sweet 200bhp – at just 9,500rpm. That’s a touch more than Kawasaki’s supercharged H2 superbike makes on his dyno, and at just 2/3rds of the revs. It’s also just over double the power made by the stock retro Z900 RS on the Big CC dyno.

The bike’s parked up outside on its side stand, and at first glance it looks like butter wouldn’t melt in its mouth. From the right hand side, standing back a little, you can’t see any sign of the turbo, hung down low in front of the engine. The only hint of anything unusual is the shorty stainless silencer – and maybe that link pipe is a bit fatter than you’d expect? Check out the cockpit though, and things get a lot more interesting. You can’t miss the white faced turbo boost gauge, with its silicone damping fluid three-quarters up the glass…

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But that, plus the sweet Z1-style aftermarket paint job, are the only clues that this isn’t a standard Z900 RS Café – until you check out the other side. Here, a honking great Ram-Air cone filter, clamped onto a beefy turbocharger, is about as subtle as a 200 horsepower kick in the face.

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I’m all set for some laughs then. I’ve ridden a few of Sean’s bikes over the years, so am expecting good things, as well as some crazy nonsense. Sling a leg over the shiny Zed, and everything feels pretty normal – fat tank spread out in front of me, wide bars, neat analogue/digital dashboard. Turn the key, press the starter, and I’m rewarded by a throaty rumble, and the cold engine settles into a fast warmup idle around 2000rpm. Click down into first and we’re away.

Wokingham is in a permanent state of roadworks it seems, so I have to take a diversion off my usual country road route, and end up trawling through the town centre traffic. The turbo Z900 is a proper pussy cat here though – smooth fuelling, with no sudden power surges –and it’s a breeze to trickle along on a whiff of throttle at 40-50km/h, filtering through the jams.

I’m out of town soon enough though, and once the 60km/h limit is past, I give her a gentle handful away from a red light. And my jaw drops nearly as fast as the front wheel lifts. Because the massive hammer blow of torque around 4000rpm is like nothing else you’ll ride. It’s more like an angry big V-twin motor than an inline-four, and it’s making 100ft-lbs by 6000rpm. But it’s much smoother than a twin too. Push me and I’d say it’s a wee bit like a gigantic Triumph Speed Triple engine – overdosed on horse steroids.

The urban sprawl is well behind me now and I’m pulling onto the motorway back up to London. The long, clear slip road is just too tempting, so I take a deep breath, and hammer the gas as hard as I dare up the first four gears. The top yoke bounces violently up and down, like a pogo-dancing punk and even when I change up into fourth gear the front Dunlop is rebounding back off the asphalt at me.

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The speedo is whizzing round much like you’d see on the latest superbikes, but with a far lazier engine note trumpeting out below me. I’m badly mangling the speed limit in a heartbeat, and only the thought of the various speed cameras that litter the UK motorways brings me back down to earth.

That turbo hit is so hilarious though, that I keep dabbling all the way up and round the M25 orbital motorway. You can trundle along at just over the 110km/h limit, all innocent, mingling with the normal folks in their normal cars. Then, with a quick tweak of the twistgrip, the boost gauge lights up, and you’re slingshotted forwards in an instant, leaving the world far behind you.

Roll off the gas, slow down to a legal-ish pace, then do it all again. Dropping a gear into fifth or even fourth heightens the experience even more, and like a gasping junkie, I keep going back for more hits of this intoxicating power and speed.

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Off the motorway a junction early, and I go for the long way home, taking in a couple of favourite local twisties. Surrey isn’t blessed with loads of TT-spec backroads, but there are a few nice test routes where I like to check out a new bike. The turbo Zed performs almost exactly as standard in terms of handling of course, since Sean’s not made any chassis mods. Plus, the extra mass of the turbo install is just about cancelled out by losing the standard exhaust system, catalysts and airbox, so we’re still in the same ballpark weight-wise.

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Not that this is a bad thing – I really like how the stock Z900 RS rides, with a stable, friendly chassis setup, comfy suspension and decent brakes. If this was my bike, I’d swap in some sportier tyres, just to give a little sharper steering and an extra margin of grip. And I’d like to try some different pads in the front brakes too, to try and get a bit more bite.

But that would be it for me. This bike isn’t really about high-end chassis tweaks and ultimate bolt-on mods I reckon – it’s about that easy-access power, from the low-priced no-fuss turbo kit. The standard Kawasaki ABS and traction control setups are still in place, and seemed to be doing their best to keep up with proceedings, and with the manual boost dial easily tweaked (even on the move!), you can potter about on ‘just’ 150bhp while commuting or cruising, then lean down to dial in an extra 50bhp should the need for speed arise…

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I spend the next week or so living with the turbo Zed, and it’s surprisingly easy to get on with. So many times over the years, riding an highly-strung ‘special’ tuned bike turns out to be more bother than it’s worth – it’s the old ‘marrying a supermodel’ paradox. Super-trick race reps and the like look like a million dollars, but are miserable to live with day-to-day.

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But this bike is the total opposite. It’s comfortable, behaves perfectly at slow speeds, and the only downside from the turbo in daily use was a light misting of oil from the open filter (apparently that was my fault for not riding it hard enough…) Cruising along the motorway at 130km/h, I flick through the dash and check the fuel consumption – 4.7L/100km says the readout, and while the larger injectors Sean’s fitted might be affecting the accuracy a little, it’s still very impressive work.

Handing the keys back, I congratulate Sean on a job well done. He’s built a good-looking, top-performing bike, with sweet retro looks, and H2-matching performance, for a great price. And he’s brought back the ‘street sleeper’ concept, with a vengeance!

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THANKS TO: Sean at Big CC Racing (www.bigccracing.com)

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ENGINE
The standard Z900 RS uses a detuned 110bhp version of the 948cc 125bhp Z900 engine, and part of that detune is a lowered compression ratio, down to 10.8:1 from 11.8:1. This means Big CC can bolt on a turbo, putting in about 6-8psi of boost, without worrying about detonation, even on standard pump fuel. Avoiding an engine strip, replacement pistons and/or a riser plate makes a big difference to the cost, and since the red line stays around the same at a lowly 10,000rpm the stock internals aren’t put under too much extra stress.

TURBO
Sean likes to keep exact specs close to his chest, but the boost comes from a modified Garrett ball-bearing turbo, with an internal wastegate, tweaked to his specifications. It’s mounted to a custom stainless steel manifold, and leads to a short stainless silencer, which is pretty much road-legal in terms of silencing.

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Another cost-saving feature is this – an old-school dial-adjustable boost control valve. You can spend thousands these days on high-end super-smart electronics to manage turbo race engines, but for this simple setup, Sean’s gone back to basics. And what could be better for a retro turbo bike than a retro turbo boost controller?!

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A subtle black aluminium link pipe leads up from the compressor wheel, sidles under the tank, then on to the billet/fabricated plenum chamber to carry out its nefarious work. There’s a lovely Tial dump valve hidden beneath there and yes – you get a sweeeet turbo ‘chirrup’ when you slam the throttle closed!

A Dynojet Power Commander plus some other mods to the fuel system pumps in enough petrol to match the pressurised turbo airflow. Super unleaded (98 RON) pump fuel makes sense if you’re riding hard and pushing up the boost, but if you turn down the dial for daily use, 95 RON unleaded is fine.

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FITTING/OVERSEAS CUSTOMERS
For customers outside the UK, Big CC can deliver the full Z900 RS turbo kit, and also provide full advice on fitting. It’s not quite a DIY job though, and you will need a dyno facility to finalise setup – but any decent tuning shop should be able to sort this out for you.

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BIG CC RACING Z900RS Cafe Turbo Gallery

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