Project Polaris RZR: Part 2 Suspension and Power

Zbroz suspension and Mountain Performance ECU

Jul. 23, 2007 By Stephen Clark

Last month we introduced the 2008 Polaris RZR project being built by Rexburg Motorsports in Rexburg, Idaho, and gave an outline of the planned modifications to the machine. We are pleased to report that the machine has received a few mods this month. This may seem like an overly-enthusiastic statement but RZR’s are extremely hard to find, and aftermarket parts are even harder. It seems that Polaris opted for a “soft” release of the RZR and has only given dealers one or two each, which doesn’t even come close to meeting the consumer demand for this machine. It seems every time we visit a Polaris dealership there are customers drooling over the one and only RZR in stock. Customers have to put their name on the list and patiently wait until the factory produces more machines.

Nevertheless Rexburg Motorsports have not only a RZR, but a modified RZR. And it has been a busy month for this particular machine as it has been hauled to shops all over for R&D. The first stop was Mountain Performance in Draper, UT. They partially dismantled the machine to begin building a prototype supercharger system.

When the techs at MPI had the machine apart they noticed that a couple of the motor mounts had broken in initial "testing" (translation - playing hard!) and needed to be replaced. Unfortunately the broken mounts had caused the engine to move enough for the exhaust heat shield to melt against the black trim on the passenger footwell.

MPI spent a couple of weeks building a prototype supercharger kit and conducted some test fits on the machine; the prototype kit was then removed from the machine so that the parts could be duplicated and manufactured. Then the project will head back to MPI for a production kit to be fitted.

RMS has four point harnesses on their RZR and is working on a full roll cage, but we highly recommend leaving the stock safety nets on the machine and rider and passenger should both always wear full riding gear. MPI’s re-mapped ECU provides a good increase in performance by raising the rev limiter, removing the speed limiter, and optimizing fuel and timing curves.

While at MPI they remapped the electronics in the ECU to raise the rev limiter, remove the speed limiter, optimize timing, and fuel curve. Internal modifications are made to the factory ECU in addition to a billet aluminum cover, this upgrade is available for the Polaris RZR, Ranger, Sportsman 700, and Sportsman 800 ECU’s. The RZR will now max out at about 70mph on flat hard terrain and also accelerates quicker.

This billet panel allows the driver to adjust compression dampening on all four shocks without leaving the seat. Prototype Exit rear shocks feature remote reservoirs, dual springs with adjustable crossover.

After a few weeks at MPI, the RZR went to the ZBroz Racing facility in Logan for some suspension work. Mike Hallock designed remote reservoir larger shocks complete with a clever in-cab compression adjuster panel. This innovative device allows the driver to adjust the compression on all four shocks without leaving the seat; this is particularly nice because the aftermarket Crowe 4 point harnesses are not very easy to get in and out of. The shocks perform much better than stock and have a much greater range of adjustment allowing the driver to better tune the suspension.

Prototype Exit front shocks feature remote reservoirs and a single progressive rate spring.

These prototype shocks use a single progressive rate spring on the front with dual sprung units on the rear, complete with crossovers that control at which point in the travel each spring is used. Dampening is significantly improved over the stock unit by increasing the volume of air and oil used. Not only does the shock flow better internally but it helps the shock to remain cool so that shocks don’t heat up and perform differently. These shocks are direct replacements for the stock units and still use the factory a-arms; the only other change to the factory set-up is the removal of the front sway bar. ZBroz are currently working on a long travel wider suspension kit that should be fitted to this machine shortly.

In the meantime, the suspension performs much better than before. We were very happy with how the front shocks performed but the rear still needs a bit more setup. Driving the RZR it seemed that the rear wanted to bottom out as the machine g’ed out on the transition into jumps. This should be fixed shortly by using different springs. Bear in mind that these are prototype units and still undergoing development and will receive a lot more development before ZBroz begins shipping shocks. At the time we rode the RZR the ZBroz technicians had only been able to make some initial adjustments to dampening and spring rates.

Jumping is now much smoother thanks to the upgraded suspension. This shot really shows the abuse that the RZR was given on our ride at the dunes.


Nate and Glen from ZBroz racing came along for our test ride and made a few suspension improvements during the day.


The RZR on its way back to Rexburg Motorsports behind the authors tow rig.

In the meantime, Rexburg Motorsports will be out testing the machine, having fun, and providing as much feedback to both MPI and ZBroz as possible to assist with their product development.

The RZR will be spending a lot of time on St Anthony Dunes in Idaho and may be at Winchester Bay in Oregon for DuneFest in early August. So if you are going to be either of those places this month keep your eye out for the RZR, feel free to come say hello and check out our progress. If not why not take some donuts over to your local Polaris shop and see if they can move you up a few places on the RZR waiting list?


ZBroz Racing Suspension


Rexburg Motorsports

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