The patent for turbocharging dates back over 100 years, with the first practical application achieved in WWI French fighter planes. Production motorcycles had to wait until 35 years ago to benefit from the technology, with the Kawasaki Z1R TC leading the way. All four Japanese manufacturers flirted with turbocharging in the early 1980s, but these efforts vanished almost as quickly as they arrived.Despite a lack of popular appeal, there still is something of a cult around turbocharging, due in no small part to the addictive nature of the power it unleashes in an otherwise ordinary powerplant.Drag racing is one natural home for turbochargers, but there are others. Harry Gunusen of American Turbo Power is a modern day pied piper of turbocharging motorcycles, and he took us into his dominion for a look.American Turbo Power is in a rugged industrial area of Van Nuys, a Los Angeles neighborhood in the San Fernando Valley. There, Gunusen builds turbo bikes for a steady stream of disciples, who often show up unannounced to simply chew the fat with the burly, soft-spoken guru.After a childhood that started in Istanbul and moved through Belgium and Australia, Gunusen got his start as a motorcycle mechanic in New York, where he owned a Honda CB750 in the 1970s. He was installing turbo kits in cars and bikes when the bug bit him.“When you drive a turbo, in a car or a motorcycle, you get hooked on that acceleration,” Gunusen explains. “There’s nothing that can compare to it. You can’t build an engine aspirated to have that kind of top-end charge. I saw the performance gains and I wanted to build it bigger and better.”Competition, of course, was inevitable. “Throughout the ’80s I drag raced, as my mechanics shop was working. I raced throughout the west coast. I held a couple of records in the sportsman classes in the Ultra Turbo classes. And then I started building bikes big and bigger, stretching them longer with bigger swingarms and bigger tires, putting car tires on them.“Over the years, I’ve had five long-chassis car-tire bikes. You start with ten second runs, and escalate to nines and eights. Before you know it I got into 12- and 13-inch car tires running 450 horsepower with gasoline and nitrous. Then I switched to alcohol turbo classes. I drag raced alcohol funny bikes, which were 500 horsepower. I’ve gone 7.16, 192 mph. I’ve ridden a top fuel Harley that was a 6.80, 198 mph drag bike.“We had a challenging build about three years ago. I was approached by a friend in San Antonio who had built a chassis to run the Texas Mile,” Gunusen says.“The chassis got built three weeks before the Texas Mile. No motor. No transmission. No turbo system. No wiring. No paint. We did it in three weeks and got it delivered back to him and it ran in the Texas Mile. The Harley bagger went 186 mph. It had a 131-inch JIMS motor in it with our turbo on it.”Of course, Gunusen is still involved in competition. “A friend of mine has a Pro Stock motorcycle and I’ve been a crew chief on his bike,” he says. “I’ve just been around racing the last 30 years, wrenching and working on them – constantly trying to improve.”Now at American Turbo Power, Gunusen has a steady stream of customers, and describes what they want. “A guy walks in with a motorcycle he just bought or has had it for a while and he wants to upgrade it and put high performance stuff on it. He doesn’t care what it costs – especially the Harley clientele. They have a new bike and they want to do a complete engine upgrade or a turbo kit.”Fourteen years ago, Gunusen had a future brother in arms walk through the door. “I have one customer, John Cabral, who came to me in 1999 and we became good friends. He has about 40 motorcycles and probably has 15 with turbos on them. We go all over the country and drag race. He lives and loves turbos. We do shows together. He’s a successful businessman. His interests are big Harley motors and turbocharged Hayabusas. He has probably five turbo Hayabusas and every type of Harley you can think of with one of my kits on them.“I built him a 124-inch 2000 Ultra Classic. That bike has made 250 horsepower and has won Daytona shootouts many times. It’s a completely loaded down bagger and has run 10-second quarter-miles. It’s a phenomenal bike.”In the American Turbo Power shop, we spied a ZX-14R. “Itís my own bike,” Gunusen relates. “That one has a Trac Dynamics swingarm, a 240 tire kit, Performance Machine wheels, and Galfer brakes. The motor is completely stock, except beefed-up clutch springs and my turbo kit. It puts out 270 to 280 horsepower. The kit is 100-percent bolt it on and go. The bike has been down the track a couple of times. It runs about 9.0 and 166 mph. With a couple more passes it should get into the 8.8s. It’s one of my ‘Sunday’ bikes, so I donít abuse it too much.”Another of Gunusen’s personal bikes is a 1980 Honda CBX. “I bought it new. I rode it stock for two years, then I built the motor – put in Carrillo rods, pistons, and a turbo kit. The suspension, swingarm, brakes and raked frame – everything has been changed, so it has been worked on from the ground up.”We asked Gunusen why he has kept the CBX for over three decades, while he has accumulated hyperbikes like the ZX-14R and Hayabusa. “It’s a unique bike,” he relates, “We drag raced it for a while, but it wasn’t too feasible. The clutches would burn up on them too often. So, it became a Sunday cruiser for me – it’s comfortable, smooth and a nice bike to ride. The bike made 235 horses, and ran a 9.60, 154 with stock shocks and street tires. It was a pretty fast bike for its time.”Revisiting the past, we spy a customer’s 1981 Kawasaki GPz1100. “It has a built 1132 motor and turbo system,” according to Gunusen. “The bottom end is all done. The gears are undercut. It had the wheels and swingarm done, and custom paint – a ground-up bike that we did that puts out 200 to 210 horsepower.”That brings us to the American Turbo Power bagger, which showcases what is possible for a practical rider who wants something special on the road. Owned by Eddie Alvarez, who let us take it out for a test ride, his Road Glide has a 95-inch motor, J&E pistons, S&S Cycle gear drive cams, a Barnett clutch, and cylinder head work. With the ATP turbo kit, it puts out 170 horsepower and nearly 150 ft/lbs of torque.“The bagger uses our flagship system for all the touring models,” Gunusen notes. ìIt runs on 91 octane pump gas, and is ridden everyday. It’s a trouble-free, “get on it and go to New York” kind of set up, with tremendous passing power. The only thing we require is that people put good quality oil in it and change it every two or three-thousand miles.”With the performance mods on the Harley motor, the ATP Road Glide doesn’t suffer from turbo lag. There is plenty of low rpm power for it to get going before the turbo starts to kick in.Once it does, the power is immense. The more you let it rev, the more the turbo comes into play. This is not an engine with a flat power curve; it is one where the power multiplies as the revs add.Lightly muffled, though the turbo tones things down a bit while adding a signature whistling sound, the ATP Road Glide has a strong street presence. Pass someone on the highway, and it will be done with an authoritative sound and rapidity – just look over your shoulder for law enforcement first.One certainly doesn’t expect a Harley-Davidson Road Glide to produce 170 horsepower, though it takes very little time to get used to it.We did have some concerns about reliability, and Gunusen addressed those. “A Harley motor like this can make anywhere from 150 to 200 horsepower,”Gunusen says. “For rideability, and everyday riding with no problems, we keep the boost down and the horsepower in the 150 to 170 range so you can get away with the belt drive. But, if the guy is a hot-rodder and he wants to really get away from stops, he’ll have to put on a chain and a good clutch.”Thanks to the other engine mods, we were more than satisfied with the power from stoplights and didn’t feel the need to rev it into boost territory for street riding – the presence of one of LA’s Finest during our ride reminded us of that.Despite the abandoning of turbocharging by manufacturers, there still is a turbo cult that has continued to do the R&D to keep this tuning option viable in the 21st century.As American Turbo Power demonstrates, the technology can be used for heart-stopping acceleration on dragstrips, as well as turn a cross-country touring expedition into an enticing excuse to flex your bike’s muscles whenever a straight line beckons.Photography by Don WilliamsThis story is featured in the May/June 2013 issue of Ultimate MotorCycling magazine — available on newsstands and good bookstores everywhere. 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