WE’VE had 600s that go as fast as 750s. We’ve had 750s that perform as well as 1000s. But never before have we had a 600 that gets to within 1mph of a Hayabusa. That’s faster than a ZZ-R1100, a GSX-R1000, an R1… the list goes on.
The 600 which achieved that momentous feat is hardly standard, but if you wanted to, you could take it out on U.S. roads. And there are three other machines equally capable of humiliating much bigger bikes – and are all road-legal, too.
I wouldn’t have believed it if I hadn’t experienced it myself. And the onlookers standing safely behind the concrete wall of Honda’s Proving Centre of California, situated deep in the Mojave desert, were equally sceptical – until they witnessed the yellow and black GSX-R600 punch its way past the timing lights at 193mph.
The word " outrageous " didn’t even come close. Yet over the past four days we’d got used to seeing four tuned middleweights in the shape of two GSX-Rs, a CBR600 and an R6 blow away the quarter-miles, top speeds and lap times of machines with 1000cc engines. We all know 600s handle superbly and boast easy, high-revving power. What we don’t picture them doing is shredding tyres and beating their bigger cousins.
Normally, of course, they don’t. But these four were anything but normal. Each was built by a top tuner from the U.S. Most of these technical experts are more famous for their work on the bigger stuff, but they were all keen to flex some muscle with a supersports machine. And four days of testing at a drag strip, an eight-mile oval and Willow Springs race circuit proved what they – and the bikes – were capable of.
Let me introduce the star players in this extreme game. Dan Kyle, of Kyle Racing Engines, chose to modify a CBR600. It looks like a racer, but it has had road essentials like headlights and a brake light thrown on.
The set-up incorporates a tall chassis with a steep swingarm angle and lots of trail, which Kyle prefers because it gives better front-end feedback. The fork internals have been uprated and are topped by Honda Blackbird bars. Standard brake discs and calipers with HRC pads and braided hoses mount to powder-coated stock wheels fitted with very sticky Dunlop D207GP Star tyres. The rear shock is a Fox item with an all-new linkage and the whole package is enveloped in Sharskinz race bodywork.
Though the motor retains the stock CBR600 crank, it has gained plenty of HRC goodies and parts developed by Kyle himself, including balanced con-rods and 3mm oversize pistons to take it out to 654cc. There are HRC valve springs, camshafts and titanium nitride-coated valve seats to minimise valve train wear.
The head has been shaved to boost compression and the rest of the engine has been blueprinted. Just for good measure, there’s an HRC close-ratio gearbox, HRC quick-turn throttle and a selection of ignition boxes with different rev limits.
Apart from the crank, the only other parts that remain standard are the carbs, airbox, air filter and clutch. Well, it’s nice to know not all the work put into developing the road bike was wasted.
But impressive as that was, our attention was diverted when HyperCycle’s Carry Andrew, a man with a long history of working with Suzuki race bikes, turned up with a thinly-veiled GSX-R600 supersport racer. The chassis was standard, but the suspension had been uprated and the motor very heavily modified.
How heavily modified we didn’t realise until later on, when we listened to the engine as it was fired off up the drag strip. No way was this " just " a 600, we thought. So we had to ask: " Just how big is this? " Andrew replied: " I’m not sure. " Cue pursed lips and quizzical looks all round.
But it was only when we saw what it could do at the Willow Springs circuit and prodded Andrew to be more specific that he admitted the cylinders were bored out to fit a set of JE pistons, while the bottom end retained the 600 crank. It’s actually in the neighbourhood of 725cc, give or take a few cc’s.
But it’s not all about cubes. Also making a contribution are longer-than-stock titanium connecting rods, a polished crank, a Barnett clutch with aluminium drive plates, a ported and polished 600 head with Yoshimura Stage 3 cams and a Yoshi valve spring kit.
The standard carbs have been junked for a set of 38mm Mikuni flat-slides, a race kit carbon-fibre airbox with intakes that run through the frame, and a full Yoshimura titanium exhaust system. The ignition system has been remapped to take revs 500rpm further and the bike runs on race fuel, which Andrew reckons is good for another 8bhp.
The work didn’t stop at the engine. The frame has been on a jig and made totally straight and the fork stanchions received a coat of titanium nitride and anodised lowers to match the frame and swingarm. The package was completed by a Penske rear shock, Performance Machine
six-piston calipers and PM Chicane wheels holding Pirelli Super Evo Corsa tyres.
And, just in case you’re thinking this is some exotic workshop fantasy designed to be wheeled out for occasions like this, check out the set of headlights mounted inside the race bodywork. Yes, this is a road-legal motorcycle.
And so is the Yamaha R6 built by Graves Motorsports. When you’re trying to get the most out of an R6, it helps to be the men behind America’s factory Yamaha superbike team – but this wasn’t something only professional racers could handle.
Owner Chuck Graves said: " I wanted to build a bike that a regular guy could ride every day. " In fact, Graves uses it on the road himself when the weather is good – as it is most days in Los Angeles.
It looked the closest to stock, with original bodywork, headlights, indicators and mirrors. However, the chassis was also the most modified, with Ohlins forks and rear shock, Marchesini wheels, Brembo brakes and a motor bristling with Yamaha Engineering Japan racing kit parts.
Graves began by stripping the bike to its frame. The swingarm received light bracing to cope with the power upgrade and Ohlins suspension on the front and back ensured the handling was rock-solid.
The engine itself is a lightly breathed-on R6 unit. There’s no big-bore add-ons here, just a few choice Yamaha kit parts blended with aftermarket ones and a bit of tuning ingenuity. The intake ports were cleaned up to take advantage of a Yamaha race intake cam and modified cam timing. Feeding the cylinders are four 39mm Keihin flat-slide carbs. Graves spent an entire week fabricating the brackets, the throttle shaft and throttle-position sensor to fit them to the engine. He said: " If you’re off by only two thousandths of an inch on a spacer, the carbs stick. "
The other side of the combustion equation is a Graves titanium exhaust. Below the stock pistons, a balanced and lightened crank helps the engine spin up quickly. A Yamaha kit CDI unit rounds out the engine changes.
So, how do all these tweaks add up? It’s almost time to find out. But before we do, meet Richard Sims. The owner of Sims Engineering is not a man with a reputation for understatement – if you’ve ever seen his previous nitrous-breathing ZX-9R you’ll know why.
His Suzuki GSX-R600 isn’t as over the top as that – well, not externally anyway. The only visible clues to his work are aftermarket brakes and a modified swingarm. Underneath, however, there’s a nitrous injection system, complete with nitrous bottle concealed in the tailpiece, and an auto-shifter. Sims built a mildly-tuned engine using a mix of Gixxer 600 and 750 parts, counting on the nitrous to give it the edge at the drag strip and top-speed venues.
A lightened 750 crankshaft spins in the 600’s bottom-end and a sleeved-down 750 cylinder with Wiseco pistons makes it " around 700cc " .
GSX-R750 cams and a light porting job complete the internal modifications.
Externally, there’s a Muzzy exhaust system and beneath the stock airbox sits a rack of 39mm Keihin flat-slide carbs, complete with a full-throttle microswitch that allows you to shift without backing off.
Sims claims the engine is good for 122bhp and 57ftlb – and that’s without the nitrous! But it’s the laughing gas that makes it so much fun – Sims reckons it adds a huge 50bhp. A Schnitz controller works with the carburettor microswitch, Dynatek ignition and Pingel air shifter to gradually feed in the gas when the throttle is opened fully in second gear.
The nitrous oxide bottle, controllers, stainless steel hose and so on carry a hefty weight penalty, however. The Sims GSX-R scaled in at 195kg (430lb) without fuel.
The Sims GSX-R was the only machine in the shootout to sport an extended swingarm for more stability and traction at the drag strip and on the top speed run. Like the others, the frame was straightened, bolted to the long swingarm and fitted with a Hayabusa rear wheel (half an inch wider than the stock 600 wheel).
Up front is another Hayabusa wheel, along with Ferodo discs and Nissin six-pot calipers to slow the bike’s mind-numbing velocities. There’s also Race Tech-modified suspension and a Hyperpro steering damper.
The stock bodywork lulls you into a false sense of security, but the license plate (as they say in these parts) reads: " A BAD 600 " . Remember, this is the USA. Look up " bad " in a U.S. phrase book and you’ll see it translates into English as " very good indeed " . And later I was to discover that it actually means: " Jeeeeeeez! " .
It was obvious from the start that Sims was willing to sacrifice the race track for the added bonus of cleaning up everywhere else. And it was on the drag strip where he was really looking for his GSX-R to dominate.
The air-shifter, operated from the horn button, is designed to get the power down incredibly quickly and make the shift as tight as possible – crucial in this discipline, where the gap between winning and losing is two-tenths of a second.
The others, beautiful to ride the rest of the time, were a bit of a handful to get off the line quickly without expensive components bouncing down the drag strip behind you. These bikes have been made to handle – and that goes against what drag racing is all about.
But that doesn’t mean they were slow. Far from it. Interestingly, both the Graves R6 and Kyle Honda CBR ran nearly identical times: Kyle’s ripped off a 10.337s run at 136.05mph and the Graves Yamaha was a tick behind with a 10.339s at 135.75mph. The Kyle Honda’s higher terminal speed reflected its superior mid-range, which allowed it to launch with greater ease and authority. But these two relied on a blaze of clutchwork and throttle balancing early on to stop them wheelieing too much.
The HyperCycle GSX-R felt so strong during its first run down the strip that we wondered if we’d been lied to and this was in fact an over-bored 750 motor stuffed in the 600 chassis. Instead of needing numerous attempts to drop its times steadily, it pounded out a 10.194s run at 143.77mph on its second pass.
A near 10mph advantage at the strip indicates a serious power advantage which was too great for it to be anything near a normal 600.
It surprised us, but the real master of the strip was yet to run. The Sims GSX-R started out impressively, but not amazingly, with an initial run of 10.389s at 140.26mph (that’s still faster than an R1, though).
But once the nitrous and air-shifter were hooked up, all hell broke loose. Using a road-legal rear tyre, it gained the necessary traction off the line and managed a stunning 9.773s run at 150.71mph. And that was with an accidental early shift into second. Unfortunately, nitrous gremlins put an end to the fun at that point. But the laughing gas gods had already left the first of their marks on this contest.
With the drag strip points going to the Sims GSX-R, we packed up for the day and headed out into the desert. Three hours north of Los Angeles lay the high-security confines of Honda’s Proving Centre. The place was in the middle of nowhere and although it was 80°C on the ground, there were snow-capped mountains all around us.
Once we’d had a trial run to get familiar with the oval, the Graves R6 and Kyle CBR again fought each other tooth-and-nail. This time, the Yamaha came out on top with a 177mph pass, 1mph faster than the Honda. To put that speed into perspective, 177mph is only 1mph slower than the top speed of a Blackbird. Unfortunately, the Graves R6 holed a piston on its last attempt to better that due to a mistaken gamble on jetting. Fortunately, it came to an easy rest – which is exactly what you need when you’re on a banked oval.
Next, the HyperCycle GSX-R demonstrated a top-end pull belying its 600 roots. But while it pulled like a superbike, it started weaving like a TZ750 on the banking – though not before it had achieved 188mph.
Even that wasn’t enough to compete with the Sims GSX-R. At first it registered a 170mph run in normally-aspirated form. A little disappointing when you consider it does a 150mph quarter-mile! But after an electrical problem was ironed out and the nitrous was on-line, the Suzuki waded through some gearing changes to put the other bikes on the trailer.
As the nitrous was linked to the air-shifter, Sims instructed me to shift manually up to fifth, then punch the button to activate the gas in sixth. That required precise timing to run past the radar gun at top speed without hitting the rev-limiter. Doing so could pop the motor.
But, for some reason, the desert wind was in our favour, the planets were in alignment and my biorhythms were at their best. I got it right. The Sims GSX-R blasted to 193mph at an indicated 14,200rpm.
The noise at full chat as I went through the gears, with the rush of the nitrous kicking in when I shifted to top, was something that should be sold in gift shops.
But while the Sims GSX-R cleaned up again, it couldn’t make it to Willow Springs. Sims knew his emphasis on drag strip and top speed was going to hurt his ability at this venue anyway, so he blew the short circuit out. " I’ll give ’em that portion, " he said.
So, Sims’ GSX-R… nul points. That left three. First up, we unleashed the HyperCycle GSX-R at the nine-turn course. But it was more of a job to get round the track quickly than we’d expected. Like you’ll hear the GP masters of the 500s saying, there’s no point in horsepower if you can’t get it down on the Tarmac. And that’s true for this GSX-R.
Its bhp-laden engine required precise throttle control to stop the rear tyre spinning excessively exiting nearly all the corners. Though we didn’t get it on the dyno, we reckon it makes about 135bhp. But while you could get away with things on the brakes and in mid-corner lean, it was a delicate art getting on the gas.
Handling and steering manners were very light, though the Pirelli Dragon Super Corsa tyres tended to fall in at severe lean angles. The brakes were more than adequate to scrub off the speed generated by the powerful engine, but their feel was a little soft, with excessive lever travel before braking actually started to kick in. But that doesn’t mean it was slow. The total package was good enough to run the quickest lap time of 1:25.92.
As usual, the Kyle Honda CBR and the Graves Yamaha R6 battled furiously, each producing their speed in a different manner.
The Honda used its stomping mid-range lunge to leap out of corners and its chassis kept high-speed matters well under control. But even with that impressive mid-range, it impressed with light, precise steering and fierce braking from the stock calipers with HRC pads.
The Graves R6 did its thing differently, keeping its real meat in the top-end of its rev range. It meant you had to work it hard – both your brain and the engine. But when kept on the boil, its smooth, quick-revving motor generated incredible speed.
The usual nimble R6 chassis made the task of line selection ridiculously easy, augmented by the fantastic Ohlins suspension action that made mid-corner bumps float away. Add the exemplary stopping power of the Brembo brakes and you had a complete package that was the favourite of the majority of the testers at the track.
And though the lap times were close, the Graves R6’s superior feel shone through– it notched a fast lap of 1:26.65 compared to the Kyle Honda’s 1:27.25. That’s quicker than you can put an R1 or GSX-R1000 around Willow Springs. Case closed.
It’s no surprise we buy so many 600s. They offer that balanced package of performance and affordability which appeals to a huge cross-section of the riding population.
But should you have the additional cash, it’s nice to know that the boundaries of middleweight performance can be expanded far wider than we thought possible.
Speed isn’t limited to the size of your machine, and horse-power merchants such as Graves Motorsports, HyperCycle, Kyle Racing Engines and Sims Engineering have shown here that their expertise doesn’t just apply to bigger hardware.
So what about the old adage, there’s no substitute for cubes? That’s just been blown out of the water.