Big Kat diary!
Or how Big CC Racing turned Suzuki’s 2019 Katana retro into a wild, turbocharged street-sleeper
Like a lot of folk, I was a wee bit underwhelmed by Suzuki’s new Katana when it was launched a couple of years ago. The original 1980s Katana was part of my teenage biking fantasies, and while I never got the chance to own one, the super-trick design, solid 80s superbike performance – plus the cool name and logo – all had a big impact on me. Back in 1981, machines like the Katana were a big part of why kids like me got into motorcycles. A Kawasaki GPZ1100 or Suzuki Katana poster on a 10-year-old’s bedroom wall generally only led in one direction – to the local bike shop six years later.
Fast forward four decades, and while the new Katana looks good and goes well, it’s some way off today’s cutting edge. It is, essentially, a GSX-S1000 naked roadster in a posh suit, with the same engine and running gear; a 150bhp version of the GSX-R1000 K5 motor, bolted into a twin-beam aluminium frame that’s also based around the GSX-R1000 design. The forks, swingarm, brakes, wheels and tyres are all the same as the GSX-S, and only the bodywork, bars and fuel tank have been changed. It’s a handsome, solid bike, but unlikely to make it on to the wall of any 10-year-old kid’s bedroom (or on the lock screen of their iphone today).
Sean Mills at Big CC was also slightly underwhelmed by the Katana. Unlike me, though, he has both the skills and the chutzpah to do something about that. And here it is, parked up outside the Big CC Racing HQ in Wokingham – a 260bhp, turbocharged 2020 Katana.
Sean’s thinking was along the same lines as his similar Kawasaki Z900 RS Café project, which we rode last year: take a popular retro-styled roadster, develop a well-priced bolt-on turbo kit, using the stock engine internals, and then bump up the power and torque to superbike-smashing levels. The kit developed for the Katana goes straight on to the GSX-S1000 too, so fans of the more conventional Suzuki roadster can also go crazy with an extra 120bhp if they fancy it.
These kits have to be subtle to work well and the Katana kit is just as slick as the previous Z900 RS set up. From the left-hand side of the bike, only a cunningly-sculpted turbo outlet pipe betrays the non-standard nature of what lies beneath. The right-hand side is more obvious, but a carefully chosen compact K&N pancake filter and black Tial dump valve camouflage the turbo install a treat. The alloy charge pipe sneaking up under the fuel tank cover is a big clue – but perhaps the starkest cosmetic difference from stock is down to the removal of the standard underslung exhaust chamber, leaving a huge gap around the swingarm pivot area.
There’s bugger-all subtle about the noise from the thing when Sean starts it, mind. The Z900 RS was fairly civilised in terms of noise, thanks to a link pipe and end can, but the unsilenced turbo Katana is as raucous as a drunk footy hooligan. Sean takes me through the kit over the fracas below. He’s had to do a bit more work on this design, because the Katana motor’s standard compression ratio is a bit on the high side, at 12.2:1, for a turbo (the Z900 RS compression is just 10.8:1). On a full-bore 500bhp race tune, you’d strip the whole engine down to fit low-compression turbo pistons along with billet con-rods and much more, but that can mean a £10k bill for the engine work alone. Here, Sean’s trying to keep the costs down for a street bike tune, so he’s compromised by using a spacer plate under the cylinder block. That raises up the block and head, increasing the volume of the combustion chamber, and thus lowering the static compression ratio. The camshaft sprockets need to be slotted so the valve timing can be re-set after moving the head up, and that’s also part of the install.
So, there’s a bit of engine work needed here, with a head and base gasket replacement as well as the spacer plate and camshaft sprocket mods. Once that’s done though, you have a low-compression engine that’s all set for some forced induction… That comes in the form of a custom-made stainless steel welded manifold, a Garrett ball-bearing turbocharger, dump valve, wastegate and pipework, leading up to a neat alloy plenum chamber under the fuel tank cover. Like the Z900 RS, the Katana also has a small manual boost controller down by the turbo, a simple knob that you twist for more or less power, ranging from 220bhp to 260bhp.
A Dynojet Power Commander and MAP sensor board look after the fuelling changes needed, and that’s pretty much it in terms of hardware. Sean’s obviously spent weeks fine-tuning the fuel mapping needed to go alongside the plumbing and turbo, and that‘s a big part of the development job too.
I’m fully briefed on matters then, and all set to go. I park up my trusty old Fazer 600, hop aboard the ear-bleeding Katana, and set off towards London. The first problem is obvious – there’s no fuel in the thing (there’s never enough fuel in a Katana…) so I stop at the BP garage round the corner and fill up with super unleaded. The 12-litre tank takes almost 11 litres and I’m assuming Sean’s set me this little trap to ensure I’m paying attention…
Back on the road, and I’m gently trundling around the various roundabouts between Wokingham and the M3. On small throttle openings, the Katana is smooth and easy to ride, with no big surprises from the power at all. The loud exhaust note reminds you that you’re on something a bit excessive, but the main thing I’m noticing at the moment is the strangely-heavy front-end. I stop at another garage and put some air in the tyres – the front is at 20psi and the rear 30psi. To be fair, this bike has spent almost all of its life on the dyno, and all the attention has been on the engine work. I also didn’t give Sean much notice I was coming, so he had no time to give it the once-over.
Now, we’re properly moving. I head out of Wokingham and get the chance to give the nowwarm engine some beans. Overtake some cars off a roundabout on to a clear bit of A road, second gear, full gas, and: BLINKIN’ FLIP! There’s a proper ‘calm before the storm’ moment as the revs pick up past 6k, and then the Katana goes nuts. What seems like a small explosion goes off underneath me, and I’m hanging on to the bars for dear life, scrabbling for another gear as the front wheel heads skywards. Change up into third, and it does the same trick (the traction control is off) and I’m experiencing the typical Big CC turbo bike thrill once again.
It’s quite different from the Z900 RS mind. That had a massive low-down dose of instant grunt, like riding an enormous V-twin. Here, the power production is a bit later in the revs, with a more pronounced hike in power from 6000rpm right up to the redline, and it’s still pulling really hard as you approach that redline…
I get home after a dose of the usual motorway madness, sampling the 260bhp available in a series of roll-ons in various gears, trying to get a picture of the performance. As ever, on full gas, Sean’s fuelling is a thing of beauty, with massive, smooth, inexorable waves of grunt launching you towards the horizon. Third gear is sensational, the power hit at 6000rpm is just hilarious, and only a sense of self-preservation and the average speed cameras lurking on the M3 gantries spoil the fun.
Next day I’m out to shoot some pics with ace snapper John Goodman. The Kat needs feeding before we go anywhere; the turbocharger obviously hasn’t helped fuel consumption and my full-gas motorway exploits yesterday have cost me dear in terms of BP Ultimate unleaded. Tank filled and we go to our favourite bends for some antics. The turbo bike is a piece of cake to potter round some gentle corners on – just like the stock Katana, the handling is easy, the weight keeps it stable, Brembo brakes are decent and the only downside is the slightly-worn OE Dunlop rubber on there. Off-boost, the engine is largely as standard up to around 6000rpm, and riding around 50-60mph for cornering photos is easy.
The only downside is the loud exhaust note, which has the curtains twitching on nearby houses. We bugger off before any keen coppers appear, heading to Box Hill to try and get a cuppa (no joy: Ryka’s is still locked down), then finish the day off with a few wheelie pics. This turns out to be harder than it sounds as it happens, partly because I’m a bit rusty after four months of lockdown and a winter without much riding, and partly because the turbo Katana isn’t an easy bike to wheelie for pics without a handy Cold War runway. This is because the power is a bit higher up; slower-speed antics are hard work; hitting the boost in first or second gear is savage; and third gear is a bit fast for photos.
The throttle response on the edge of boost is really tricky. As the power comes in, you’re feathering the throttle back and the torque falls away, so you’re chasing the drive all the time. Once you’re up in the power, it all smoothes out a treat, but by then you’re the wrong side of 60mph – not ideal for wheelie pics on the road… So – this is a long, whiney apology for the ropey wheelie pics essentially: I will do better next time, promise.
I’m really impressed by the turbo Katana though, rubbish wheelies aside. It’s not a hugely practical everyday machine of course – the Katana’s small fuel tank and offensive exhaust note would grate after a month or so (the noise itself would earn me a divorce and an eviction notice). Sean does offer a link pipe and silencer as with the Z900 RS, and I’d definitely consider the extra cash for that. And if you must have your 260bhp with touring ability, the kit will also go straight on to a large-tanked, faired GSX-S1000F.
The fact remains though that the engine performance is something else. Motogp-level power from a bolt-on kit that starts at around £4k is hilarious. It takes the bike to a whole new level
– and I can definitely see a 260bhp turbocharged Katana setting off a few ex-teenagers’ middle-aged biker fantasies, poster or not…