Cycle News

VOL. 50 ISSUE 49 DECEMBER 10, 2013 The Street Tracker tended to grind the exhaust on its left side, but Matt Capri says that problem has been cured with the pipes getting raised. short skirts. These deliver 11.5:1 compression (stock Bonneville is 9.2:1) - in spite of which the Tracker motor still runs on regular pump gas, yet delivers 106 hp at the rear wheel at 7500 rpm on the same Dynojet rig that had clocked the stock Bonnie motor at 61 hp. That's right: 70 percent more horsepower, in a bike 25 percent lighter than a stock Bonnie - and an equal injection of extra torque, which now maxes out at over 80 foot pounds at 4200 rpm, up from 47 foot pounds as standard. That's mucho mojo! This requires Capri to raise the gearing from the stock 17/42T to 19/38T - the equivalent of a massive 10T off the rear wheel. To harness this substantial increase in torque and power, the stock five-speed Bonneville transmission has been beefed up with a Barnett multi-plate Kevlar clutch, with stiffer springs that have differential rates to dial in some progressivity to the pickup. The key to this huge increase in performance is the modified Bonneville eight-valve cylinder head, which South Bay's Rick Kemp has ported and gas-flowed via a five-angle valve job, then fitted soup plate-sized one-piece stainless steel valves that started out life on the local Toyota deal- er's parts shelf. The result sees 36.5mm inlet valves no less than 6mm larger than stock, and the 31mm exhausts are 5mm over, all fitted with custom-made Teflon-coated dual valve springs with shim-under-bucket titanium retainers. South Bay Triumph's own high-lift camshafts with substantially longer duration and serious overlap are fitted, ground to Capri's spec. Finally, the head is fitted to the crankcases using a three-layer MSL head gasket that's rubber-coated to prevent any blow-by leaks with the higher compression, and there's a Swedish-made oil cooler hung under the steering head to counter the extra heat spun off by all that power. Twin 41mm Keihin FCR flatslides replace the stock 36mm CVs, bolted to CNC-machined billet intake manifolds, with a tapered bore blended into the flowed head. Fitted with a pair of K&N filters, the Keihin flat-slides are married to South Bay's airbox kit, which delivers a significantly freer-breathing package whose extra revs are unlocked via remapped Triumph Performance ignition box. Using Nology coils, this allowed Capri to dial in an extra 2000 rpm over the 7200rpm rev-limiter programmed into the stock Bonneville ECU. The final part of the tuning equation is the Lubricor exhaust with separate twin stacked pipes P77 running down the right of the bike, based on the system that Capri designed for Triumph USA's official Thruxton Cup one-make road race series. These feature 1¾inch diameter ceramic-coated headers, and each incorporates a reverse-cone megaphone located within the similarly shaped outlets. The result is a muscular exhaust note that isn't too offensive, yet still sounds fruity. Throwing a leg over the Street Tracker reveals the minimalist seat to be pretty comfortable, with the low but quite rear set location of the flip-up footpegs delivering a great riding position for what has to be the ultimate traffic tool. That's thanks to the Triumph's slim build, an extremely tight steering lock that makes feet-up U-turns in narrow city streets a piece of cake; and a relatively tall, upright stance that gives a great view ahead over car roofs. The Tracker's simply ideal for lanesplitting your way to the front of the line at stop lights, or zapping through freeway traffic at speed; or best of all carving canyons in the hills above the Pacific Ocean, where the Triumph's direct, quick steering and agile handling really come into their own. For this ideal traffic tool isn't some kind of über-maxi scooter, but a potent, torquey Supertwin that's incredibly easy to ride in spite of its considerable performance. To access this, just turn on the gas, forget about the

• Cover