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2008 RACE TEST SUZUKI RM-Z450

March 4, 2008
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From a human standpoint, you have to feel for Suzuki. For the 2008 model year, they decided to roll the dice on a fuel-injected 450cc motocross bike. It was a bold move; one that could insure their place as the most adventuresome of the Big Five. The pot of gold at the end of the rainbow was a massive increase in bike sales, fueled by the mystique of EFI (Electronic Fuel Injection). There were risks, but it wasn’t a “Hail Mary” pass. It was an aggressive marketing ploy to leapfrog to the front of the pack. The 2008 Suzuki RM-Z450 is the first mass-production fuel-injected motocross bike (at least one year ahead of Honda, Yamaha, Kawasaki and KTM) and that could have resulted in jam-packed dealerships.

Unfortunately, the bike was delayed for months. Insider reports say that there was a flurry of small problems each time release was imminent (including an idler gear that reportedly howled like a jet engine). The delays meant that Suzuki dealers did not have a 450 on their showroom floors during the most lucrative selling season (from August to December of 2007). Instead, the RM-Z450 introduction was pushed back until snow blanketed a large portion of the the mainland. As a result, Suzuki will produce fewer 2008 RM-Z450s than it did 2007 models.
MXA understands the ups and down of gambling, but what really matters to the consumer is how good the 2008 Suzuki RM-Z450 is. Our report is very in-depth.

Q:WHAT’S NEW IN THE 2008 SUZUKI RM-Z450 ENGINE?

A:Here is the complete list:
(1) The crankshaft is located approximately 2mm farther back and 3mm farther down in the engine cases.
(2) Flywheel inertia has been increased 1.7 percent by the addition of heavier magnets.
(3) The port angle has been changed from ten degrees to 25 degrees (with 15 percent more downdraft).
(4) The cams are new, and the intake port has been reduced in diameter, increased in length and straightened.
(5) The head features narrower valve angles; the intake valves have been changed from 13 degrees to 11.5 degrees and the exhausts from 13 degrees to ten degrees; for comparison, a fuel-injected Suzuki GSX-R600 sport bike has 12-degree intakes and identical ten-degree exhausts. Additionally, the squish area has been opened up on the sides of the combustion chamber to improve flame propagation. The compression ratio is 12.2:1
(6) The head pipe is titanium, the mid-pipe stainless and the muffler aluminum.
(7) The transmission has been upgraded from a four-speed to a five-speed.
(8) Instead of a carburetor, the 2008 Suzuki RM-Z450 features a Keihin fuel injection system managed by a 16-bit processor.

Q:DOES FUEL INJECTION REQUIRE ANY SPECIAL PARTS?

A:Does Paris sleep on silk sheets? Suzuki’s fuel injection system requires nothing but special parts. How many? What are they? Here is a quick list. (1) The gas tank has to have outlet and return fuel lines. (2) The fuel lines have to be able to handle 42 psi of pressure. (3) To work, an EFI system requires a fuel pump to get gasoline into the nozzle with significant velocity. (4) Even though there isn’t a carburetor per se, there is a Keihin throttle body that encompasses the injection nozzle (with 12 ports), a butterfly valve (which replaces the slide) and a progressive throttle linkage. (5) The CPU electronics have to be able to manage the input from five sensors (throttle position, water temperature, air temperature, intake air pressure and tip-over angle).

Q:HOW DOES THE TIP-OVER SENSOR WORK?

A:Imagine the surprise of the first Suzuki test rider to scrub the prototype 2008 RM-Z450, only to have it shut off in midair. The solution was a sensor that insured that the engine keeps running at angles in excess of 60-degrees. The tip-over sensor provides fuel delivery for 20 seconds when the rpm is below 3000 rpm and for five seconds when the rpm is in excess of 3000 rpm.

Q:DOES THE RM-Z450’S EFI NEED RACE GAS?

A:No. In our opinion, race gas would be a big mistake. The fuel injection system doesn’t like the chemical makeup of race gas. Running it can increase maintenance and the risk of clogging the injectors.

Q:CAN THE SUZUKI RM-Z450 BE HOPPED UP WITHOUT THROWING THE FUEL INJECTION OUT OF WHACK?

A:Yes and no. There is a level of performance that would require a new map in the ignition, but where the breaking point is located depends on what kind of mods are performed. The 2008 RM-Z450 will accept an aftermarket exhaust system without banging. It might accept an increase in its 12.2:1 compression without squawking. It starts to get questionable when you combine a port job, high-compression piston and exhaust system. Suzuki’s engineers aren’t sure where the tipping point is, but they admit that there is a horsepower increase that will exceed the window of the stock map.

Q:IS THE STOCK ECU PROCESSOR PROGRAMMABLE?

A:No. You will have to buy an aftermarket box from Yoshimura or other hop-up company. There are ports to make changes, but no readily available program that defines the stock parameters.

Q:HOW MUCH PRESSURE IS IN THE FUEL LINES?

A:Approximately 42 psi. What does that mean? It means that you cannot fiddle with the fuel lines (which are special nylon reinforced hoses that have to be firmly attached to reduce the risk of spewing fuel under pressure). It also means that the 2008 RM-Z450 should be able to resist boiling the fuel better than the 2007 model (because fuel under pressure has a higher boiling point than unpressurized fuel).

Q:DOES THE RM-Z450 HAVE A BATTERY FOR THE EFI?

A:No. Power for the electronic fuel injection comes from a magneto.

Q:WHAT IS A MAGNETO?

A:A magneto is an electrical generator that creates a high-voltage pulse rather than continuous current. It is the reverse of an electromagnet in that the magnets move past the armature to induce a small amount of current, but at an extremely high voltage (which a 10,000 microfarad condenser levels out). When you kick start the RM-Z450, you are operating your own personal power station.

Q:DOES IT START EASILY?

A:Yes. According to Suzuki’s engineers, it should take two or three kicks to provide enough electricity to operate the RM-Z’s fuel pump. The MXA test crew could almost always start it with one kick once it was warm (although we had to use the hot start).

Q:IS THE RM-Z450 FRAME IDENTICAL TO LAST YEAR’S CHASSIS?

A:Would you believe that virtually every part has been changed, but that the dimensions remain the same? It’s true. The frame is lower, but the seat height is the same. The extrusions are thinner, but the head angle is unchanged. The triple clamps are lighter, but the offset is still 21.5mm. You gotta appreciate the fact that Suzuki’s engineers redesigned virtually every part of the chassis, but didn’t change its essence.

Q:WHAT ARE THE BEST TRAITS OF THE 2008 RM-Z450?

A:There are three really significant attributes of the ’08 RM-Z450.
Handling: The MXA wrecking crew loves Suzuki’s take on handling. Suzuki’s four-strokes handle like two-strokes. While many 450cc bikes handle like runaway trains, Suzuki has gone a full degree steeper on the head angle, 2mm less on the offset and much more agile on the response scale. Matched against the CRF, YZ-F, KX-F and SXF, the Suzuki RM-Z feels like a 250F.
Jetting: It’s crisp. Very crisp off idle, and the cleanest-running bike we’ve ever ridden through the midrange. It’s got issues above that.

Ergonomics: The 2008 RM-Z450 feels light. It is slim, trim and svelte. If you closed your eyes you would never guess that you were on a 450cc motocross bike. The kicker is that it isn’t actually light. It’s 3.3 pounds heavier than last year. The extra pounds come from the five-speed tranny, jumbo-sized fuel pump and EFI throttle body. You can feel the extra weight when putting the bike on the stand, but nary an ounce is evident in motion.

Q:WHAT ARE THE WORST TRAITS OF THE 2008 RM-Z450?

A:There are five significant problem areas on the ’08 RM-Z450.
Shifting: The MXA test crew has never missed as many shifts on a Suzuki before. If you rushed a shift, you could end up in neutral. Why? The bend of the shift lever is so obtrusive that your boot catches half way up the lever arm instead of on the shift knob. This lessens leverage. Even worse, there have been shifter linkage problems.

Forks: After our bad experience with the 2008 Honda CRF forks, we are beginning to believe that Showa has lost their way. The RM-Z450 forks are poorly set up. They are way too soft, which makes them feel very harsh as they reach midstroke. Worst of all, they bottom harshly.
Axle blocks: The first time we adjusted the chain using the axle block guides the rear wheel wouldn’t spin. Once we centered the wheel accurately, we discovered the axle marks were off two full hash marks.

Top-end: MXA test riders learned to make the most of the crisp low-to-mid powerband, because the power is soft on the top and banged into the most obnoxious rev limiter we have ever felt.
Flame-out: There is a learning curve to fuel injection, and one of the bugaboos is flameout. What is flame out? It is a jet fighter term that refers to the engine cutting out. The RM-Z450 tended towards flame-out in two situations. (1) At very low idle settings, like cruising into the pits, the engine would cough and die. (2) At the end of fast straights, when test riders chopped the throttle abruptly, the engine would shut off. This reminded us of the early ’90s light-flywheel RM250 two-strokes, which were prone to flame-out under off-throttle/hard braking situations. The solution is to pull the clutch in when ever you chop the throttle and slam the brakes on.
   
Q:HOW FAST IS THE 2008 SUZUKI RM-Z450?

A:If we are comparing the 2008 RM-Z450 to the 2007 RM-Z450, that isn’t a very hard target to hit. The 2007 model was pleasant, amiable and mellow (which are code words for slow). Every test rider felt that the 2008 RM-Z450 was stronger off the bottom and through the middle than the previous RM-Z. But, and this is a big but, it’s nowhere near the KX450F or CRF450 when it comes to real world thrust.

Q:HOW DOES THE 2008 SUZUKI RM-Z450 RUN?

A:We’d be lying to you if we didn’t admit that the EFI RM-Z was weird to ride. It had elements that were terrific, some that were mediocre and some that were awful. Here is a breakdown of traits:
Terrific: Throttle response was awesome. From the moment you rolled the throttle on until it started to give up the ghost on top, the jetting was perfect. The bike wanted you to blip the throttle, play with power settings and metered the delivery to suit the terrain. From low-to-mid it was a blast to ride. Its best surge came very low in the rpm range, but it wasn’t arm wrenching. Just a solid pull off the bottom.

Mediocre. The power delivery was an amalgamation of sensations. First, the 2008 model may be totally different from the 2007 model, but the fruit didn’t fall far from the tree. It is it still a pleasant, amiable and mellow engine. Second, after a great start off the bottom the power softens as the rpm rises. At the point where the KX-F, RM-Z and SXF start to go into overdrive, the RM-Z begins to back down.

Awful. The 2008 RM-Z450 signs off early (it starts to wane before 10,000 rpm). This is no big deal if you avoid over-revving and never try to stretch one gear to the next corner. A savvy rider will heed the warning signs. If you hit the rev limiter, the engine goes spastic. It pops, bangs and backfires. Surprisingly, when you shift to the next gear, the RM-Z450 pops and bangs a few more times for good measure. Obviously, hitting the rev limiter causes a seriously lean condition, and that leaness carries over for a few seconds (even after you apply fuel to the top-end).

Q:WHAT IS MXA’S VERDICT ON THE POWERBAND?

A:Amazingly, the MXA test riders liked the way it ran, but there is a caveat. This isn’t a traditional 450cc four-stroke. If you ride it head-to-head against its more powerful competitors, you will lose. Instead, we suggest that you consider the 2008 RM-Z250 to be an RM-Z350. For all practical purposes, it should be ridden like a 350cc engine in a 250cc chassis. The ergos, cornering, agility and crispness of the low-to-mid engine make it feel more like a very powerful 250F. This bike is suited to riders who are willing to ride hard, shift often and dive to the inside when ever possible.

Q:DID WE HAVE ANY PROBLEMS WITH THE 2008 SUZUKI?

A:Yes. We blew the cases apart. The kick start idler gear bound up in the cases, cocked sideways and cracked the center cases horizontally. Not good. Not pretty. Not something that we ever expected to happen. It’s a shame, but for the MXA wrecking crew this was a deal breaker. There was nothing we could have done to prevent the cases from breaking…we have to hope that there is something that Suzuki can do.

In the interim, since our test of the 2008 Suzuki RM-Z450, Suzuki held the production bikes up, changed the ignition timing to stop kick-back (which is what Suzuki believes caused the idler gear to break the cases). Additionally, Suzuki made some reported changes to the gear shift selector (which we also saw break during the course of our testing, but not on our test bikes).  Suzuki feels that these changes will elminate the problems that MXA had (and we have since put many hors on two different RM-Z450s without any more breakages).

Q:WHAT ABOUT THE JETTING?

A:What jetting?

Q:HOW WAS THE SUSPENSION ON THE 2008 RM-Z450?

A:The forks were terrible. You can ride the bike with the stock setup, but you can’t race it on a true-to-life motocross track. The forks are undersprung to the extent that they limit speed as much as the rev limiter.
Go stiffer on the fork springs. Suzuki did try to stiffen up the spring rates (they went from 0.46 in 2007 to 0.47 in 2008), but they stopped too soon. We changed the stock 0.47s to 0.49s. Once you have the correct springs, you can raise and lower the oil height to meter the midstroke.

Q:WHAT WAS OUR BEST FORK SETTING?
 
A:For hardcore racing we recommend this fork setup:
Spring rate: 0.49 kg/mm (0.47 stock)
Oil height: 370cc (was 385cc in ’07)
Compression: 11 clicks out
Rebound: 11 clicks out
Fork leg height: 5mm up
Notes: If the RM-Z450 oversteers, slide the forks down in the clamps until they are 2mm above the top clamp.

Q:WHAT WAS OUR BEST SHOCK SETTING?
   
A:For hardcore racing we recommend this shock setup:
Spring rate: 5.6 kg/mm
Race sag: 100mm
High-compression: Two turns out
Low-compression: Eight clicks
Rebound: Seven clicks
Note: Heavier or faster riders can go to a 5.8 kg/m shock spring.

Q:IS THE FIVE-SPEED BETTER THAN THE FOUR-SPEED?

A:Given the fact that the 2007 RM-Z450 wasn’t a powerhouse engine, the four-speed tranny tended to wheeze from gear to gear. A five-speed is a better choice because it offers a wider selection of gears, magnifies the available power and offers a lower first gear and a taller fifth (than with the four-speed).

Q:COULD WE FIND NEUTRAL ON THE 2008 RM-Z450?

A:Yes. The shift mechanism was changed from the old geared ratchet to a linked-cam.

Q:WHAT ABOUT THE TIRES?

A:Last year the RM-Z450 was part of the wide-tire movement with a 90/100 up front and a 120/80 on the rear. For 2008, they have returned to conventional-size tires (80/100 and 110/90). The MXA test crew prefers the 110 rear tire on virtually every 2008 bike (especially the KX450F and YZ450F). Suzuki’s tire choice is a Bridgestone 403/404 combo. The 404 is a decent rear tire, but lose the 403 front to get the most out of the Suzuki chassis.

Q:WHAT IS THE CAPACITY OF THE ALUMINUM GAS TANK?

A:The RM-Z450’s gas tank holds a miniscule 1.6 gallons of gas. How can it get away with so little capacity? The fuel injection doesn’t waste as much fuel as a Keihin FCR carb.

Q:WHY IS THE GAS TANK MADE OF ALUMINUM?

A:Suzuki’s official answer is that the aluminum allowed them to maintain a much slimmer profile than with a comparable plastic. But if we were guessing, we’d surmise that the aluminum tank offers a stronger foundation for the internally mounted fuel pump and to resist pump suction collapsing the sides. Additionally, the aluminum tank enables Suzuki to meet new EPA rules about the permeation of fumes through plastic gas tanks (without having to resort to coated plastic).
 
Q:WHAT DID WE HATE?

A:The hate list:
(1) Shift lever. We think that the RM-Z450 wants to shift accurately, but that the odd shape of the shift lever hampers it. You will learn, by experience, to avoid hitting the bend in the lever.
(2) Reliability. Yikes!
(3) Axle blocks. Don’t trust the chain adjustment marks.
(4) Power. We wanted more.
(5) Rear brake. We smoked it.

Q:WHAT DID WE LIKE?
 
A:The like list:
(1) Pump Gas. There are a handful of riders who think that race gas is required on their four-strokes. It’s not (and in the RM-Z450 it could clog the injectors).
(2) Starting. It was easier than Suzuki said it would be.
(3) Handlebars. You gotta love the Renthal FatBars.
(4) Handling. It is razor sharp. It won’t be everybody’s cup of tea, but it’s uniquely different from every other 450 four-stroke.
(5) Footpegs. The new pegs are 5mm wider than last year and borrow “positive draft” from the Lightspeed pegs. What is positive draft? It defines a footpeg shape where the opening at the bottom of the pegs is larger than at the top?which means that mud falls out instead of sticking.

Q:WHAT DO WE REALLY THINK?

A:We liked it, but we didn’t love it. It could be faster, better suspended and more reliable. The first year of any totally new design is fraught with peril. In all fairness, this bike was rushed through pre-pro testing too fast. It needs more testing. It will be better in 2009.

 

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