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The BMW KI isn’t perhaps everyone’s idea of the ideal turbocharged sports machine, but there’s no denying that its weight and aerodynamic bodywork should keep things reasonably stable.

Then again, anyone who dials in maximum boost and tries to extract a possible 300bhp - and 200mph plus top speed - from the Luftmeister K1 isn´t likely to be a stable type of personality..

Oddball? Definitely. But the Luftmeister BMW comes from a company based in Long Beach California with a long track record in tuning - and improving - the German BMW machines.

The violence is all the more memorable for being so totally out of place. Trickle along with the revs below 5000rpm, and you would never suspect that this was anything other than a typically tame BMW sports-tourer.

Snap open the throttle with boost showing on the gauge, though, and things turn wild in a hurry. The K1 leaps forward like a pouncing tiger. Its turbo-hiss under hard acceleration is interrupted, when you back off to change gear and the wastegate opens momentarily, by a weird fluttering noise, as though the beast has swallowed a large bird.

Ignore it and get back on the throttle. With your head down, peering past unfamiliar dials and lights then through a dark screen, the K-bike slices through the wind towards a top-speed limited only by its standard gearing. BMWs were never meant to be like this.

In one respect such an unsporty bike is hardly suitable for the turbo treatment; in another way it’s perfect. Bolting Luftmeister’s turbo kit onto a K1 is like slipping an iron fist into a velvet glove. On the outside the BMW remains soft and inoffensive. But it carries a punch that would shake a standard ZZ-R1100.

Luftmeister boss Matt Capri has been tuning BMWs since he helped build Reg Pridmore’s Daytona-winning boxer superbike in the Seventies. The name means "Air master", and the firm from Long Beach in California has been making K-series models blow harder since 1988. Now 50 years old, Capri clocked over 199mph at Bonneville on a turbocharged K100 in 1989, and is confident of cracking the magical 200mph figure this year.

This bike was built to demonstrate his latest road going turbo kit for the K1. Beneath the bulky bodywork, set low in front of the engine, is an IHI turbocharger, plumbed with a large aluminium intercooler. Below the tank, a second bank of fuel injectors, made by MSD in Texas, helps out the standard system. A single, Luftmeister-designed exhaust pipe runs along the left side of the bike to a neat alloy silencer.

The view from the rider’s seat gives more clues, starting with the boost gauge in the fairing. A row of coloured lights, set in a console on the top yoke, flickers as the revs rise and fall, denoting the changing fuel: air ratio. This bike, Luftmeister’s development machine, also has a small computer box fixed to the screen to allow rapid fine-tuning of the engine management system.

The K1 is the personal bike of Luftmeister technician Mattias Dobner (who spent seven years in BMW’s Munich R&D department, working mainly on K100s, before leaving for America) and is a stage up from a normal kitted bike. Its turbocharger is larger, and set to give almost double the normal 8psi of boost. Where the stage one kit lifts peak power from 80 to around 160bhp on Luftmeister’s rear-wheel dynomometer, the bigger unit pumps out 200bhp. "The basic kit doubles the horsepower and pushes the standard gearing to its limits right away, yet you can drive it all day through the desert," says Capri. "The big turbo with 12 to 15psi makes almost three times the stock brake horsepower. With what we call ‘dialaboost’ you can turn it up to 25psi. But we only sell this kit to people who we feel are qualified and won’t hurt themselves, because this bike will go ballistic.

Surprisingly little is necessary to keep the engine together even at that output, according to Capri. "The K1 motor is incredibly strong with stock crankshaft, pistons and rods it will take over 300bhp and still be reliable," he says. "The way BMW make the crankshaft with five main bearings means there’s no flexing. As long as you prevent detonation you’re not going to have any failures."

Nevertheless Mattias’s bike has been fitted with an upgrade for its single-plate clutch, plus the larger oil-pump from a two-valve K100. Dobner recommends the swap, especially when running over 8psi of boost. "The number five main bearing and the camshafts are the vulnerable parts of this engine, and the slight power loss with the bigger pump does not matter with a turbo." Apart from cooler plugs and stainless oil lines, the engine is otherwise standard.

The kit also includes front brake pads and heavy-duty fork springs, to which this machine’s specification adds several optional chassis modifications including thicker fork oil, EBC brake pads and steel brake lines. Its rear shock is a combination of Progressive Suspension body with Luftmeister’s own spring, while Luftmeister’s rear-wheel spacer provides clearance for a respectably wide 160/70 section Metzeler ME1.

For all that, the BMW felt deceptively standard as I followed Mattias, on another turbo K1, through LA traffic towards some of his favourite roads near the Pacific coast. The turbo is set to come in only at half maximum revs of around 5000rpm (less on the standard kit) and below that figure the bike runs on the standard fuel-injection set-up.

At low revs it was barely discernible from a stock bike. Tickover was perfect, the clutch light, and the 16-valve motor as docile as ever. The only unusual feature was a very slight glitch, just off idle, which meant that to avoid stalling it was advisable to build a bit of boost by blipping the throttle slightly before letting out the clutch.

With the tacho above 5000rpm, though, it’s a totally different story. The first time I opened up the K1 was on a freeway on-ramp, and I won’t forget that moment in a hurry. With boost showing on the gauge the response was instant, and instead of lumbering forward like normal the BMW accelerated as though fired from a supergun before plunging into the freeway’s normal slow-moving river of pick-up trucks and people-carriers at a suicidal rate. The front wheel will lift at low speeds but this is no uncontrollable wheelie-bike; it’s too heavy (around 270kg) and too long for that. Instead it just accelerates with unfamiliar enthusiasm, storming through the first three gears despite the typically slow change, and then stretches its legs in fourth and fifth to keep on pulling hard long after the standard bike would have run out of power.

The uprated chassis came in useful shortly afterwards, too, when suddenly Mattias took a left turn, put his head down and shot up a steep uphill road that opened out into a series of high-speed sweepers. As test-roads go this one was just about perfect, and the K1 didn’t let me down. Despite a typically top-heavy feel, the BMW’s uprated suspension, powerful brakes and stickier-than average tyres meant I could just about keep the speeding Dobner in sight.

You still would not want to race a well-ridden GSX-R or similar on a twisty road; even this hotted-up BMW hasn’t the poise, the ground clearance or the instant straight-line speed for that. But despite its bulk and sleepy geometry the K1 handled well, staying stable in a straight line and only feeling slightly uneasy under cornering forces that would have had a stock bike in trouble.

The K’s weight and an inevitable touch of turbo-lag makes a point-and-squirt riding technique advisable, but the boost builds quickly and smoothly provided the revs are kept above the magical 5000rpm figure. This is one BMW that really encourages you to use high revs especially in top gear, where the K1’s power keeps on coming as the speedometer needle moves round the dial with an urgency its makers surely never imagined possible.

This bike’s gearing had been returned to standard to suit LA traffic and the twisty back-roads, which meant the K1 would have had no trouble pulling through the 8500rpm redline. With taller gearing (Luftmeister can supply kits) and nitrous-oxide assistance it was recently timed at 185mph, despite a damaged crankshaft bearing caused by the hasty rebuild required after an American magazine tester had wrecked the motor in nitrous-assisted acceleration testing.

Luftmeister’s Bonneville figures prove what a turbocharged BMW can do, and, as Capri says, the main limit to a turbo K1’s straight-line performance is the amount an owner can afford. "The new bike we’re building has a long-rod engine that has already been tested to 14,000rpm," he says. "We estimate it’s putting out nearly 300bhp. The bike should be good for well over 200mph when we go to Lake El Mirage later this year.

Luftmeister’s standard K1 turbo kit doesn’t come close to matching those figures, and even the more heavily tuned bike I rode is only roughly on a par with the best of the less powerful but lighter Japanese opposition. But providing competitive performance from a BMW is a major achievement. And the best thing about Luftmeister’s impressively refined turbo K1 is that it combines serious speed with traditional BMW values. As Matt Capri says, "You’ve got the performance and you’ve got everything else" the style, the image, the sophistication. The only trouble is, it’s expensive.

At $5500 for the complete turbo kit, plus extra for the chassis parts, it certainly is. Luftmeister prefer to fit the kit themselves, too, which adds to the expense (they’ll pay half the cost of shipping from Europe). But for BMW pilots with a need for speed, the K1 turbo is the only way to fly.

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