WE RIDE PIONEER’S BIG-BORE SUZUKI RM-Z475

June 15, 2006
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NAMED AFTER THE EMBARRASSINGLY SHALLOW MTV SHOW, WHERE CELEBRITIES SHOW OFF THEIR  HOMES, SHOES, CARS AND SPAS, THE “CRIBS EFFECT” HAS SPREAD THROUGHOUT EVERY SOCIAL STRATA OF AMERICAN SOCIETY.

Pssst! Wanna know a secret? Four-stroke buyers are bucks-up. They are better off financially than any group of motocross racers in the 35-year history of the sport. Suddenly, it appears as though everybody in America is rich?ostentatiously so. Modern racers are more than willing to spend beaucoup money on their prize possessions. Pipes, triple clamps, graphics and carbon fibernothing is too good (or too expensive) for the modern four-stroke rider.

Glory road: What is the cheapest and easiest way to get more power out of a four-stroke? Cubic centimeters. Best of all, it doesn’t cost cubic dollars.

Sociologists have a name for the alarming rise in conspicuous consumptionit is called the “Cribs Effect.” Named after the embarrassingly shallow MTV show, where celebrities show off their homes, shoes, cars and spas, the “Cribs Effect” has spread throughout every social strata of American society. Everybody is pretending that they are rich by buying big trucks, big houses and big wheelswhether they can afford them or not.

Which leads us to the 2005 Suzuki RM-Z450. It’s a clean machine that has built a strong following for its easy-to-use powerband, two-stroke-style handling and passable suspension. It is not pretentious. Far from it. It’s a good bike, but not showy.
 
Every MXA test rider liked the Suzuki RM-Z450 engine. They didn’t love it, but found it to be charming, usable, interesting and, most importantly, up-to-snuff. How does it run? It’s a little passive off the bottom (worsened by overly generous gearing choices at the factory), very strong in the middle, and adequate on top (although a little flat in the higher rev ranges). The RM-Z’s charm is that it gets the job done without violent hit, locomotive chug or John Force-style acceleration. Instead, the charisma of the RM-Z is based on the fact that it is smoother, less chuggy, broader and easier to use than the competition. The mellow bottom-end, which takes its time from gear to gear, is highlighted by an amped-up midrange and a metered pull into a top-end that seems to back itself down as the revs near the limiter. Its most descriptive adjective is “nice!”

NICE IS NICE, BUT IT ISN’T THE KIND OF ADJECTIVE THAT MOST HARD-CORE MOTOCROSSERS WOULD LIKE TO HAVE ATTACHED TO THEIR RACING POWERPLANT. EVIL! ANGRY! POTENT! BRUTISH! LUSTY! NOW, THOSE ARE ADJECTIVES!

Nice is nice, but it isn’t the kind of adjective that most hard-core motocrossers would like to have attached to their racing powerplant. Evil! Angry! Potent! Brutish! Lusty! Now, those are adjectives! They speak to the whirling dervish in all of us. Nice, schmice, give us gusto!
That was our goal. The MXA wrecking crew set out to build an adjective-worthy RM-Z450. Knock-’em, sock-’em; slam-bam, thank you ma’am; barn burner! But we are smart enough not to ruin the best attribute of the RM-Z450 powerband (its ease of use) in search of quasar, Death Star-style power. You might think that by trying to make it fast without hurting its “everyman” allure, we had placed ourselves in a quandary surrounded by a conundrum (or between a rock and a hard place). Not so! There is one tried-and-true way to up the adjective quotient without making your knuckles turn white. What is it? The fabled big-bore.

Sponsorship: MXA’s Pioneer RM-Z475 was the result of a cooperative effort of sixteen different companies.

The big-bore is the cheapest, quickest and easiest way for a four-stroke tuner to produce more power without inducing heart attacks. As a rule, big-bore kits improve throttle response, increase torque and slow down the revs. That combination results in a bike that accelerates harder out of turns, pulls taller gears and stays on longer throughout the range. This is a win-win engine mod. Going large is the simplest way to make manageable power on a thumper.
There is one caveat: big-bore engines are illegal at AMA 250 Pro events, but not for Vet classes or local races (especially ones that don’t distinguish upper limits).

MXA packed up its RM-Z450 engine and sent it to Tom Morgan Racing (TMR) to turn it into an RM-Z475. Extensive testing on the new breed of over-square four-stroke engines proves that 475cc is right in the wheel house of big performance without the big feel. TMR bored the cylinder out 2.5mm, added a 98mm CP piston (with 13:1 compression ratio) and ported the head. The total cost of the engine work was less than $850. And, for that money, we got a seven-horsepower increase over the stocker. Better yet, we didn’t just gain seven horsepower at peak, we gained it everywhere (and exceeded ten extra horses after peak).

IT WAS JUST AS EASY TO RIDE AS THE STOCK RM-Z450 ENGINE, BUT MORE SO. WHERE THE RM-Z450 WAS PLEASANT, THE RM-Z475 WAS PURPOSEFUL. EVERY MILLIMETER OF THROTTLE ROTATION DELIVERED SERIOUS FORWARD THRUST.

It was awesome. No, make that marvelous. Astonishing. Unimaginable. Amazing. Make it any adjective you want, because it was just as easy to ride as the stock RM-Z450 engine, but more so. Where the RM-Z450 was pleasant, the RM-Z475 was purposeful. Every millimeter of throttle rotation delivered serious forward thrust. The weakest point of the stock RM-Z450 powerband is the bottom end. The tall gearing of Suzuki’s four-speed tranny needs a lot of juice to jump it up to the next gear ratiojuice that the stocker is lacking. Not so with our RM-Z475. It was a gear better in every situation. Things we did in second on the stocker, we could pull off in third with the big-bore.

Every MXA test rider loved the way the RM-Z475 ran. It was stronger than the RM-Z450 at every point on the powerband and, best of all, it delivered the extra power with a metered, steady, metronome-like vibrato. If we owned a 2005 RM-Z450, we’d turn it into a 475 in a heartbeat. 
With the engine buttoned up (and down pat), we moved on to the rest of the chassis.
Gearing: The stock RM-Z450 comes with a 49-tooth rear sprocket. We went to a Sunstar 50. It made second gear shorter, but made third usable in 80 percent of the corners on a motocross track. 
 
Jetting: We ran 91-octane pump gas with the stock jetting. It should be noted that we paid slavish attention to fuel screw settings at every race. If you run oxygenated VP U-4, go up one main jet.

Clutch basket: MXA test riders don’t want to risk losing hard-earned horsepower to clutch problems. We installed a complete Hinson clutch (basket, pressure plate, inner hub and outer cover). This is what Team Suzuki uses. 
   
Radiators: In our experience the RM-Z450 runs hot, proven by the fact that if the starter delays dropping the gate, you will be spinning on radiator fluid. To fix this, we installed larger Fluidyne Powersports radiators. Then, just to be safe, we ran Red Line WaterWetter.
Ignition: TMR put a Vortex X-10 ignition in our RM-Z475. We kept the X-10′s switch on the zero setting (on the box) and in the “Race” setting (at the handlebars). We never used the “Start” position (not even on the start).

ITS ENORMOUS, BEATING, 475CC HEART ISN’T VISIBLE TO THE OUTSIDE WORLD. THERE IS SOMETHING SUBVERSIVE ABOUT A FLASHY BIKE WHOSE MOST IMPORTANT PART ISN’T OSTENTATIOUS.

Suspension: To achieve a better feel, MB1 modified the suspension. The MB in MB1 stands for Mike Battista, who recently tuned the suspension of Team Honda before going out on his own. Racing the stock RM-Z and the MB1-equipped 475 was an eye-opener. Most MXA test riders were satisfied with the stock Showa settings until they tried Mike’s settings. In motion, the fork and shock were plush and fluid.

Graphics: Mitchell Bailey designed the Pioneer Electronics livery. Pioneer has a successful race car program and has shown interest in motocross over the last five years, but is still not attached to any major team.

Miscellaneous: We chose Renthal (FatBars), Dunlop (756 Race Replicas), Works Connection (hot start, radiator braces and oil caps), Uni (air filter), Ceet (seat cover), Cometic (gaskets), Pivot Works (bearings) and Regina (chain) to outfit our RM-Z.
The best thing about MXA’s Pioneer RM-Z475 is that the core of the machineits enormous, beating, 475cc heartisn’t visible to the outside world. There is something subversive about a flashy bike whose most important part isn’t ostentatious. It doesn’t say, “Look at me.” It says, “Watch me disappear.” o

SUZUKI RM-Z475 SUPPLIERS WHO, WHAT, WHY AND WHERE?
Ceet (760) 597-1077
Tom Morgan Racing (909) 889-3010
CP Pistons (949) 567-9000
Fluidyne (800) 358-4396
Cometic Gasket (800) 752-9850
Cycra (740) 929-0188
Hinson (909) 946-2942
FMF (310) 631-4363
Klotz Lubricants (260) 490-0489
MB1 (951) 371-5045
Regina Chain (410) 221-2800
Renthal (800) 222-4296
RG3 (714) 630-0786
Sunstar (937) 743-9049 
Uni Filters (714) 535-6933
Works Connection (530) 642-9488

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