SuperBike - October 1999
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**** Article reprinted with permission **** Copyright SuperBike 1999 - Unauthorized duplication prohibited
Triumph Sprint ST Turbo
A 160bhp Touring Bike? That'll Do
The Americans are knocking out turbo kits for just about every suberbike under the sun these days. Roland Brown goes Stateside to ride a Triumph Sprint with teeth.
The violence is all the more fun because it seems so unlikely. One moment there you are, sitting comfortably upright at the controls of your ultra-efficient British sports-tourer. Your personal effects are safely stowed in the Triumph Sprint ST's jolly useful colour-matched panniers. The three-cylinder engine purrs in a refined fashion as you pull effortlessly away from the lights. Snicking into second gear with the tacho needle somewhere in the middle of the dial, you casually wind back the throttle - and suddenly the world explodes into crazy action. Like Prince Charles instantly transformed into Keith Flint, your aristocratic British steed leaps viciously into the air and attempts to smash your visor with its top yoke as the power of 158 demented polo ponies is transmitted through its rear tyre. Stiffening your upper lip, you gamely hang on to the bars as the front wheel eventually touches down, and flick up through the gearbox to the accompaniment of a soft clashing sound from low down in front of the engine. What the hell just happened ?
A few brief, mind-warping fierce seconds later you back off with over 160mph on the speedo, the tach needle buried in the red and the rampaging bike showing no sign of running out of steam. Welcome to the Turbo Connection Triumph Sprint ST, arguably the nastiest, most deceitfully inoffensive-looking wolf in sheep's clothing on two wheels. Were it not for its boost gauge plus the discreet Turbo stickers on its fairing and panniers, there would be barely a thing to differentiate this bike from any of the other examples of Hinckly's finest all-rounder. Yet the cunningly concealed addition of an American-made turbo kit transforms the triple from sensible superbike to rampaging hooligan.
Not that the standard Sprint ST is exactly slow, y'unnerstand, but this is different. The turbo-triple's peak rear-wheel output is 158bhp at 9,500rpm. That's not just an increase of more than 50% on the standard max of 99bhp, measured on the same Dynojet dyno, it's also slightly more than Suzuki's Hayabusa typically makes at the rear wheel. Given that the Hayabusa has a genuine top speed of 190mph, that suggests that with the correct gearing the sober-suited British gent would be good for well over 180mph, even wearing panniers laden with cucumber sandwiches and flasks of Earl Grey. The guy responsible (if that's the word) for this bike comes from the aptly-named Rapid City, South Dakota, USA. Brian Olson is a 27-year-old motorbike freak, engineer and computer buff who cut his teeth turbocharging cars in the late 'Eighties, moved on to 200bhp four-cylinder blown snowmobiles and then,, after building a turbo Triumph of his own, set up in business last year, under the name Turbo Connection, to sell kits exclusively for the British triples.
Ask him, "Why Triumph?" and he has plenty of reasons. "I just like them. They're something new, something different, yet they still have a heritage." More practically, he adds "having three cylinders and fuel-injection makes adding a turbcharger a lot easier. You don't have to worry about the carb jetting, making sure you've got the right main jet and needle. With theses fuel-injected triples it seems like they always run perfectly."
Olson's kit, which cost £3,000, is based around the compact, American-made Aerocharger unit which, until recent years, has been successfully fitted to bikes ranging from Harleys to Honda Blackbirds. It's a variable-vane turbo, meaning that maximum boost level is controlled not by a wastegate but by changing the positions of the turbo's vanes. To increase boost you close them up, to reduce it you back them off to allow some exhaust gas to escape directly down the exhaust pipe.
"One great thing about the Aerocharger is that it has hardly any lag " Olson says. "And the three-cylinder engine helps too. With a four-cylinder engine you get the number one and number four cylinders trying to counter-act each other, so you don't get such a clean pulse. With a triple the firing order is cleaner. They really spool up quick." Olson's kit includes the turbo (which has its own sealed lubrication system), a purpose-made aluminum airbox, intermediate exhaust pipe (standard cans are used), an intercooler, boost gauge, slightly stiffer-than-stock Barnett clutch springs, and a supplemental computer, which works with the engine management system to compensate for boost pressure. Reduced compression ratio is not necessary, Olson says, so the cylinder head does not have to come off. He says an average owner could fit the kit in about a day or so.
Boost can be set to either six or eight psi, using a small switch mounted on the frame. Standard pump fuel is fine at the lower setting, which lifts peak output to 142bhp. Olson says the higher eight psi, 155bhp-plus setting is also okay on normal super unleaded, provided you use max performance in small doses. "If you're going to stretch it out for a long time you'd need an octane booster for sure."
A big feature of the Sprint's turbo was that it was so unobtrusive, both visually and when I was riding the bike at a gentle pace. The blown motor's idle was very regular, low-rev response good, and the only thing that really gave away the turbo's existence was the slight rumbling noise from the unit itself. Even the clutch action seemed barely stiffer than stock as I headed off for another thrash on the usefully long roads around Daytona in Florida.
For Trumpet owners looking for serious speed with apparent reliability, this kit really is in a class of its own.
TRIUMPH TURBOS - Sound Idea or Expensive Blow-Up?
The great thing about fitting turbos to modern superbikes is that once you've paid yer money for the kit and fitted it, that's all there is to do - and so long as you don't go too mental it should all work out just fine. Installation, Olson insists, requires no special parts and is so easy a chimp could do it.
"For the Sprint you remove the seat, gas tank, fairing lowers, airbox, oil lines and exhaust. You bolt on the new headers from the kit, then the turbo itself. Fit the exit pipe and muffler, bolt it all up and that's the turbo part done, " he says. "Bolt on the kit oil lines and the heat shield that goes over the header pipes, then fit the charge tube that takes the air from the turbo to the intercooler. The intercooler mounts to the airbox bracket, then from that there's a pipe to the aluminum kit airbox. Three rubber boots clamp that to the throttle bodies."
Other work includes modifying the electric motor that controls the idle, mounting the boost computer in the tailpiece and connecting its wiring, and fitting the K&N filter, kit oil lines, boost gauge and switch. Hm, sounds like a pretty smart chimp to me.
The Sprint fairing and other bits go straight back on. Speed Triple and 955i models require minor mods to radiator hoses, and the 955 needs half an inch trimming from its fairing. "I can fit a kit in six or seven hours. If you've not done it before you'd need a little longer," Olson reckons. "But once they're fitted they're dead reliable. I did 4,100 miles on my 955i, I've got a customer with a Speed Triple who's done 3,200 miles, another with a Sprint who's done 2,700 miles - all with no problems at all."
Unless you forget to top-up the oil, of course, in which case you'll instantly wreck your motor and won't even be able to blame it on the turbo.
Turbo Connection are at: 2019 Eclipse Avenue, Rapid City, South Dakota 57703, United States. Tel: 001 605 393 0816. E-mail: Turbo595@aol.com
Eric's note: There is also a Turbo section on this site - Click Here to go there now.