Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/128310
South Bay Triumph Bonneville 1000 55 bolt-on flatslides and a modified airbox morphed into the creat ion of So uth Bay's Bonneville 1000 SS streetro d - complete wit h big-bore moto r and a wh ole lot of att itude . Even the n, Capri had or iginally just planned to make a one -off showbike to attract customer atte ntion. "The whole idea was really not to build t his bike as an aftermarket specia l, just to get peo ple to co me to the store to take a look at it," he says. "But I gues s because the facto ry-fresh Bo nneville isn't focuse d on perfo rmance. it seemed to hit a nerve, and after it got featured in magazines, I started gett ing calls from people w ho wanted to buy o ne just like it - as well as 38 FEBRUARY 11,2004 • other U.S. Triump h dea lers w hose custome rs wanted the same th ing. We 've shippe d a bunch of bikes all across the cou nt ry, and now we're looking for dist ributors in Europe and Aust ralia, and even Japan, to handle our kits. It' s an aftermar ket business t hat just kind of happ ened but we're now getting repeat orders fro m dealers w ho have happ y custo mers fro m t he first bikes we se nt them." To create the para llel-tw in Best of British answer to a desmo due Duc ati Mon ste r M900/ I 000 , Ca pri took a stock Bonneville and bor ed the 86 x 68mm 790cc engine 6mm ove r w ith flat-top Arias pisto ns fitte d with custom high-perform- CYCLE NEWS ance rings and wristpins 3S percent lighter than stock, running in specially made crosshatched big-bore iron sleeves and giving 10:I compression (stock is 9.2: I). This cre ated a 92mm-bore 944cc motor delivering 84 hp at 72S0 rpm at the rear wheel compared to 61 hp from the stock Bonnie. That's right: 40 percent more horsepower, and an equal injection of extra torque, which now maxes out at 66 ft.-Ibs. at 4800 rpm, up from 47 ft-Ibs. as standard. Not too shabby, especially as Capri hasn't yet found a way aro und the factory revlimiter program on the stock Sagem ignition (for which Triumph has so far declined to supply access codes), and power is still building when that cuts in. "But I will! Several of our com peti to rs said boring them out couldn't be done, but that's o kay because we pro ved it could, and re liably at that; with the stuff we have in there , we could run th is thing to I 1,000 rpm if we wanted to," says Capri, w ho now offers a three-way hop-up opti on with a pair of kits o n either side of the o riginal 944cc upgrade. This already req uires the cran kcases to be machined to acce pt the bigger pistons, same as his 97-bo re 100Scc maxi-twin motor, which in addition calls for a T6 billet-alloy South Bay Moto cylinder block, CNC-machined from solid w ith aro und a 2S percent bigger fin area for the air/oil-cooled motor. However, fo r those w ho prefe r a drop- in option retaining the stock cylinders and with no nee d fo r machining, the re 's a 92-bo re version de live ring a Ducat i-e sque 904cc capacity, using the same bo re an d stroke as the 900 Monste r's moto r. It's your call. Irrespective of t he bo re size selected, Capri t hen po rts and gasflows the eight-valve cylinder head via a beaut iful five-angle valve job typical of the SoCal tuning school, fits 2mm-larger custom -made stainless steel inlet valves using blanks made in Germany, but retai ns t he stock exhausts - although all valves are now fitted with Dayto na springs (with a custom t itanium option) - and backcuts t he inlet valves to flatte n the include d angle slightly. The global res ult is about 2S percent mo re flow than on t he stock head. Capri then installs his own pair of cam shafts w ith six degrees more duratio n and I mm extra lift ("They're a Stage Two grind - the first ones we re too mild!"). Two 42mm Mikuni flatslides replace the stock 36mm Keihin CVs, inco rpo rat ing a choke bar on the mounting rail and bolted to C NC -machined billet manifold st ubs, 40th Anniversary matched to the inlet ports and blend ed into the flowed head . Fitt ed w ith a pair of K&N filters, th ese are mar ried to South Bay's airbo x kit, which includes a separate battery bo x and various hange rs to optimize installation and increases filter surface area a massive 41 times ove r sto ck, acco rding to Capri, to deliver a significant ly freer- breathing package . "That' s w hy you have to go from a lOS main jet on the stock Bonneville to a 13S on any of ours!" says Ca pri. ':Actually, you get better economy, because it' s a more efficient motor - we get SS mpg on our Bonneville SS develo pment bike , and that 's not toy ing aro und w hen we ride it," The final part of the equation is the exhaust system , featur ing a set of stock headers, ceramic-coated and matched to a set of slip-on Toga reverse -con e "silencers" - well, you wa it unt il yo u hear them before you ask abo ut the quo tat ion marks ... To harn ess this substantial increase in torque and power, Capri retains the stock five-speed Bonneville gearbox, but he beefs up spring pressu re on the cableope rated wet clutch w ith a set of 30 pe rer cent stiff Barnett heavy duty springs and swaps the stoc k IlT countershaft sp rocket for an 18T one to gea r the SS up in orde r to take acco unt of the e ngine 's extra performance. Though a heavy density of Highway - Pat rol cars stopped me from confirm ing this during my day in the saddle , Capri says the 944cc Bonneville w ill run to 137 mph before it hits the limiter - eight mph faster tha n the stock Bonneville, and still pulling. I believe him. However, that's not what grabs you first abo ut the Bonneville SS when you ride it it's the light controls coup led w ith the effortless gru nt of t hat motor, and the ultraflat to rque curve makes sho rt -shifting effortlessly aro und 6000 rpm all t hrough the gears t he preferred o ption. The power curve is totally linear and acceleration punchy and satisfying, with the lo ud but me llow blat fro m the Toga silencers delivering t he trademar k acco mpaniment to getting it on good , '60 s-style, o n a British tw in, as the Bonnie's fro nt wheel first lifts lazily the n hovers above the pavement hard on the gas in the bottom two gears . The gearshi ft is very crisp and clean, and in spite of the heavier springs, the clutch action isn't too stiff, so take- up is smooth off the line at any of the sto plight GP races you can't help but turn any red light into plus using it in traffi c arou nd town is noth ing like as fraught for the continued health of yo ur left hand as any Ducati's clutch is. It also does n't snat ch like on e of those, either. Plus the Triumph's desmodro mic pos it ive -retu rn throttle linkage o n the Mikunis employs just a Single very light