Australian Motorcycle

Australian Motorcycle : Kawasaki ZR1100 Custom Z-1

This article was originally published in the 1995 October issue of Sport Rider.

In 1973, every motorcycle magazine carried a milestone motorcycle on its cover: the original Z-1 by Kawasaki. After one glimpse of the magazines, it was my mission to acquire this fastest of all motorcycles. And I did.

 

Doug Meyer’s retro Z-1–replica restyling job is true enough to the original to hoodwink more than a few enthusiasts. The ZR gathers a crowd anywhere it’s parked.

When the original Z-1 was in development in the early ’70s, it was code-named by Kawasaki R & D as “The New York Steak.” That “steak” was finely aged and bred until it became the finest slice of motorcycle meat on the plate. Over a period of 11 years, the 903cc Z-1 became the GPz1100 and, in Eddie Lawson’s capable hands, the AMA Superbike Champion KZ1000R.

With such a history, is there any doubt that the son of Z-1, the ZR1100, would be a very nice motorcycle and would be one that I would also want to play with in this age of sport bikes. Can you call the ZR1100 a sport bike? I think so. A motorcycle doesn’t need swoopy plastic bodywork or the latest cutting-edge components to be a sport bike. What I need is a motorcycle that makes me smile when I look at it, goes where I point it and tickles my inner sensor that screams yeah! when I gas it.

 

Due to a lack of drop-in aftermarket alternatives, Meyer stuck with the stock pistons and their 1062cc displacement. But being a hot-rodder at heart, he couldn’t resist milling 1mm off the cylinder deck height to bump the compression ratio another 1.5 points. Standard dual-plug heads handle the additional compression on pump gas without a problem.

The ZR1100 did most of that right off the showroom floor, but I wanted just a little more. With such a heritage, it’s not surprising that the ZR1100 engine is torquey, smooth and exciting. Any production engine must include compromises for drivability, fuel tolerance, emissions and so on, but I wanted just a little less compromise.

The ZR’s dual-plug head and digital ignition are designed specifically to forestall the onset of detonation, which means that more compression was definitely a workable option. Unfortu­nately, at the time I was building this bike, there were no high-compression pistons available for the ZR engine. Earl Minkler at Valley Machine in Livermore, California, milled 1mm from the top of the cylinder assembly, effectively bringing the head closer to the crankshaft. This raised the piston in relation to the head and put more of the piston into the combustion ratio, up to 10.5:1 from the stock 9.0:1. As good as the stock ports are, who can resist a little “port and polish”?

 

The ZR comes from the factory with dual-plug heads (a trick Muzzy used in Eddie Lawson’s championship-winning KZ1000s in the early ’80s), but the shiny port and polish is the work of Kawasaki Motors Corporation’s technical trainer Walter Rainwater. His huge polished ports would work better on a more radical engine. Our mildly modified mill lost midrange and ridability due to reduced intake velocity at low- to mid-rpm levels.

Walter Rainwater, south and central technical trainer for Kawasaki Motors Corporation, had his way with the head. Walter has many years of experience on Z hemis and he knew what modifications would best improve the flow figures. The resulting head is one of those pieces of mechanical art that you just hate to cover up. The large round ports flow gently into a precise, unshrouded three-angle valve job, just the way the flow bench likes it. Part of the reason the stock ZR pulls so well in the midrange is its relatively small (34mm) Keihin CVK carbs. I wanted to keep the stock carbs for that reason, but when the bike was ridden and put on the Race Shop’s (Ventura, California) dyno, the results were less than we had hoped for. Walter’s beautiful porting job was probably perfect for a pro-stock drag engine, but its huge port didn’t produce enough intake velocity in the rpm range in which the rest of the relatively mild engine was designed to work.

 

As one of the final touches, Meyer went to Corbin for a custom saddle complete with an orange ZR logo. Although there’s nothing wrong with the stock seat, passengers might not care much for this one. Corbin makes two-up seats, too.

As a temporary fix, the Race Shop’s Jake Van Vleet fitted a rack of 39mm Keihin CRs from Sudco and spent countless hours dialing in the jetting and fiddling with the airbox until the ZR showed improvement on his Dynojet dyno. The stock cams are quite mild, so Megacycle Cams was commissioned to regrind them with slightly more lift and duration. Cam design was kept mild so the cams would be of the “drop-in” variety, enabling ZR owners to use them without requiring a change of pistons. R & D Springs of Hesperia, California, manufactured a set of valve springs compatible with the cams. Jeff Myers carefully assembled the ZR engine, using a 104-degree lobe center cam timing figure to enhance the already-potent midrange lunge of the ZR. In the ’70s, you just weren’t tuned in without a Kerker pipe on your Z, so that’s what we had to have. The Kerker looks just right and lets the “enhanced” ZR breathe a little better as long as the loud competition baffle’s in place. With the street baffle, it flows less than stock.

 

Kosman Engineering did a masterful job of widening the stock 4-inch rear wheel another 1.5 inches to allow the fitment of state-of-the-art high-performance rear tires. The 180/55ZR17 Michelin M89 looks wide and mean, and wears well, too.

As fast as Z-1s were for their time, we would have killed for some of the chassis components found on the ZR. But there’s always room for improve­ment. Lindemann Engineering of Santa Clara, California, was given the task of blueprinting and revalving the forks for a little more sporting use. Valving was changed to increase the rebound damping and decrease compression damping, and stiffer springs were added. Out back, the stock shocks were replaced with fully adjustable Works Performance units calibrated for sport riding.

To take full advantage of the upgraded suspension, new rubber was in order, and Michelin M89 Radials were selected. A wider rear wheel would be needed for the 180/55ZR17 rear, so Kosman Engineering from downtown San Francisco did one of its beautiful rim-widening modifications to increase the rim width by one inch. Spectrum Powder Coating applied its usual flawless finish in just the right shade of orange. Stopping performance was brought up to par by installing Kevlar pads by Braking U.S.A. in the stock ZX-11–style calipers. The original Z-1 defined the era of the birth of sport bikes, and I really wanted to recreate that original Z-1 look.

 

Lindemann Engineering reworked the ZR11’s fork with stiffer springs and revalved damping rates. Lindemann increased rebound damping and low-speed compression damping while decreasing high-speed compression damping. The fork produced a firmer, better controlled feel, especially in sport-riding situations. Note the chromed plastic front fender—it looks just like the original.

To cap this project off, I called on Joe Cook at Cook’s Body in Sacramento, California, and asked him to copy the classic Z-1 paint. He recreated the original root-beer-and-orange paint scheme to perfection. Stock handlebars were retained for classic looks and when riding at the Pace; conventional sport handlebars allow more flexibility and control than racer-replica clip-ons. Finishing touches are a beautiful Corbin Gunfighter seat, a chromed front fender (just like the original Z-1) and a polished chain guard. This ZR looks great and proves that slick bodywork isn’t all that makes a beautiful sport bike..