It’s easy for the general public to look at a high-end custom motorcycle and just assume that it’s a collection of parts, all slapped together. But, nothing could be further from the truth, because cashed-up, discerning buyers expect absolute perfection in both form and function when they write that big cheque. So, to ensure they never let a customer down, AC-Sanctuary periodically builds a bike to further develop their products and keep them at the top, as the kings of the resto-mod. This particular bike is the personal machine of company owner Hiroyuki Nakamura, built as if he were the highly selective customer who would accept only the very best. The result is RCM-644, a Suzuki Katana GSX1100S, which is simply a sensational street machine, packed with new tricks that future customers will be able to pick.
It tells you a lot about the entire team at Japan’s AC-Sanctuary that even when they are considered the absolute leaders in their field, they’re still pushing the envelope and seeking to improve on perfection. Nakamura-san has been in the game for decades now, he has over a thousand custom bikes to his name, 700 of them in the RCM range, as well as a host of lap record holding race bikes across various classes. But he’s still pushing the limits hard and working with the biggest companies in the industry to make that possible. AC already works with the likes of Ohlins, Brembo and Sunstar, and Nakamura-san is currently in Italy, partnering with OZ Racing to bring their incredible wheel technology that is used in MotoGP and WSBK, to the streets of Japan.
But this bike features other products that have been developed of late, and to ensure the build was cohesive, in-house mechanic Nagai was chosen to head up the entire process. As with all AC builds, the process starts with the stock frame going into the model-specific jig and ensuring everything is first arrow straight. The usual strengthening program follows, with large gussets added around the headstock and swing arm pivots, while the left side of the frame is extensively modified to ensure the driveline offset works with the new big tyre combo. An entirely new subframe has been built for the bike, and the area around the upper shock mounts is pushed out to 295mm to provide greater stability.
The lower shock mounts slot into the wide Sculpture swingarm, and small cams are used to allow the shocks to be both raised or lowered, and also moved further forward or back, so the geometry can be set up properly when the bike is complete. The shocks themselves are Ohlins Blackline, with anodised parts to match the colour scheme of the bike. The front end features the in-house steering stem kit to ensure the offset is spot on, and dropped through the billet triple trees are a set of fully adjustable Ohlins forks, with some seriously trick lower legs. To complete the front suspension, AC have developed a new steering damper setup with Ohlins, with the full kit ready to go on sale in September of this year.
The wheels are, of course, OZ Racing items, but these might be some of the last 6-spoke pieces you see, as AC are working with OZ to bring the 8-spoke technology from MotoGP to the street, including the specific coating which improves heat dissipation. The braking is all of the sort of stuff you’d see in WSBK, with the billet Brembo GP4-RX calipers providing insane stopping power and are matched up to Sanctuary’s own discs, built with Sunstar. The rear end follows a similar path with the parts suppliers used, but a new caliper support improves initial braking power, especially handy for those who like to use the back stopper on track to get these big bikes turned in.
The looks are absolutely stunning, the original factory silhouette is retained for those lovers of the Katana’s true ’80s vibe, but in truth, there are almost no factory parts used. The front guard and rear hugger are AC’s own carbon fibre parts, while that iconic front fairing is all new glass and includes some clever styling changes that give it a smoother, more flowing effect. Here you will see some of the other new parts to come out of the company, billet stays and billet indicator mounts. The side covers and rear cowl are also true to the original styling, while including subtle changes to work with the widened frame, and the paint and graphics package is simply stunning, all picked out by Nakamura-san to suit his personal taste.
And when it comes to his number one desire, that’s bulk horsepower in a reliable package, and the short block is all built at the company’s sister brand next door, DiNx. There are simply too many things done to the engine to list, but from the fresh crank, to the balanced rods and the newly honed and machined block, the high compression 74mm forged pistons result in a capacity of 1135cc. The head features a similarly impressive overhaul, and Yoshi cams and gears ensure the big Suzuki donk won’t run out of air. To keep temperatures under control, a 13-stage oil cooler is fitted, and a one-off rear oil tank is being trialled, with a temperature gauge fitted on the dash to see how effective the setup is proving to be.
On the outside of the engine, it’s all the best bits money can buy, from the digital ignition that allows for multiple maps, to the snappy Mikuni flatslide carbs in a bank of 40mm units with twin stack carbs. To help save weight, the guys are also trialling a BS lithium battery, which tips the scales at next to nothing, while still having the power to crank over such a monster motor. The exhaust is another in-house branded product, a full titanium Nitro Racing system, but Nakamura-san went with a one-off carbon muffler and a sweet stainless steel hand-fabricated hanger to give his bike a custom touch. The end result is not just a brilliant bike, equal parts beautiful and blisteringly fast, but it’s also a working test bed, allowing AC-Sanctuary to hold onto their mighty crown.
[ AC Sanctuary ]