When an engine builder tricks out the Pro XP By Allen Knowles and the staff of Dirt Wheels

Allen Knowles and his co-pilot wife Roxanne use The RZR Pro XP 4 for finding adventures wherever there are trails and destinations. He has this car dialed in well.

When new UTVs come out, we often have them for a day or two of testing at a new-model introduction. That gives us enough information to share our impressions with you. Other times we end up with the unit to do more testing and even make modifications. That is the case with our RZR Pro XP 4. We’ve had it long enough to log lots of miles in the hands of CT Racing’s Allen Knowles. Knowles has been a racer and engine builder for many years. He has strong opinions about what he expects in terms of comfort and performance from any sort of motor vehicle. He is lucky enough to have support from his wife and adventure co-pilot, Roxanne. He wanted the Pro XP 4 to have the performance to keep a smile under his Arai helmet, the comfort to keep Roxanne happy to go along, and the setup ready and able for all-day or even multi-day adventuring. Here he gives a rundown on things he liked about the car and others he wanted upgraded or changed to make it a better destination trail car.

Knowles keeps a pair of Pro Armor seats on hand for new cars. If they turn into full project builds, he orders new seats, but in the meantime, the trusty seats go in after the initial testing is complete.


First up is power. More is better, and in the case of turbo UTVs, that’s an easy fix if you don’t live in California. Grab a Dynojet Power Vision re-flash. The Dynojet does some cool stuff. It gives the RZR a better tune. Just adding fuel adds power and cools the motor down, but the Dynojet re-flash turns up the boost, adding even more power, and it still runs cooler! All of our dyno testing on the Power Visions for various turbo models have gained 15–20 rear-wheel horsepower, and this one is right in line. In addition to adding power, the re-flash reduces lag time from brake to throttle. The delay is always annoying. We want to go from brake to throttle immediately to help us get off the corner, and with the flash the delay is gone.

Four-seater sport UTVs look long, but they get around most tight trails just fine. It is surprising how rarely the middle of the car drags bottom.
This is the Dynojet turbo charge tube that replaced the split stock one. It comes with the fitting, and Dynojet also sells the billet blow-off valve to enhance reliability.

Fan control turns on at a lower temperature and keeps it running longer to aid cooling. The Power Vision plugs into the ODB port and just takes a few minutes. It comes with several options, like running all stock as we are, or you can choose a setting to support modifications.

You make changes if you add parts later. You can even put the stock tune back in. You can make changes as many times as you wish. The only thing is, the Power Vision is paired to one vehicle, so you can’t use it on multiple units.

With the seat bases turned flat, the rear is a flat platform. Knowles keeps a cooler, tools and equipment there. That is better for handling than adding more weight to the rear.


Maintain your side-by-side. We drive aggressively in an environment hostile to a motor, or any mechanical device. Just because it has a steering wheel, it does not mean it should be maintained like your car. Consider it more like a dirt bike. We never go more than 500 miles between oil changes, and 300 miles is a more common service interval for us. We’ve been using Maxima service kits that include synthetic oil and an oil filter packaged together.

Our XP still has a stock cage, so we haven’t mounted the S&B Particle Separator yet, but we have been using the S&B replacement filter. It is a dry filter, like stock, but unlike stock it can be cleaned a few times. It has a larger surface area than stock, offering more flow and more power.

Buy a couple of each so you have them ready to install, and tighten up your service intervals. If you simply leave it on your “get around to it” list, you may skip service and thrash your ride. Even if you choose not to use these products that we highly recommend and know work from our testing, use something and service that car!

We wanted to carry fuel. We found the 3-gallon RotoPax fuel can (with one of their mounts) goes easily into the front of the bed lying flat. It is held securely with the RotoPax mounting bracket, but still leaves lots of room for storage.


For the West Coast, we like a tire with more side bite, usually helped by a more flexible sidewall. GBC Mongrel and Terra Master tires have what we like. Either of the GBCs allow us to get on the throttle harder, exiting corners, generating more speed and fun. Knowles grabbed five Terra Masters in 32-inch—almost the same size as the stock tires. Now all four tires and the spare match. Terra Masters have an A- side and B-side to the tire.

We ran the A-side out (soft terrain side) for our testing, as much of our terrain is sandy with hard patches. We mounted them on tough, good-looking 15-inch Raceline Mamba beadlocks.

If you upgrade to a beadlock, you can drive on a flat if you get a flat that will not accept a trailside repair. Without a beadlock, if the tire pops off the bead, you will have a very hard time getting the car to go anywhere.


One of the new features we really like is how the XP Pro bed floor pops out with the removal of four screws. That is much easier than other RZR models, giving quick, easy access to the motor for service and cleaning. This is a cost-saving design if you’re paying a shop to work on it.

Normally, we have to buy a mounting system to carry the spare and strap it down. With the XP Pro, the spare will just rest on top of the bed plastic. All you need to purchase is a “Y” spare-tire tie-down strap. Clip it on the seat mounts and the center tie-down spot in the bed. It leaves you plenty of room in the bed to haul all your gear, as it sits about 11 inches over the bottom of the bed.


The only failure the car had was at 600 miles. The turbo charge tube burst after throttling up off a corner. The stock charge tube is plastic. Our weekend-saving emergency repair required a piece of 1 1/8-inch bathroom sink drain we found at a hardware store. Shove that drain pipe in a couple of inches each way, add a couple of hose clamps, and the MacGyver fix should get you through the weekend like it did for us. Knowles had never had this happen, despite many miles in the turbo RZRs. 

The permanent fix was a high-quality, four-layer silicone charge tube from Dynojet. It comes with a billet-aluminum pop-off valve. We have heard of the stock plastic pop-off valve failing as well.

Al and Roxanne felt the stock seats were too low for good comfort and visibility. Rather than removing the stock seat brackets, Al fabbed a quick and dirty bracket that allows the seats to be removed with the stock releases. A bonus is that the seats are roughly 4 inches higher. The difference in comfort was most pleasing for taller folks. CT is working on having the brackets manufactured.


Although many are spending money on internal shock modifications and spring upgrades, Al dialed ours in as well as it could be with what we had. The setting addressed ride height. Getting it down helps handling and softens things up. The rear was set at 14.5 inches from the ground measuring to the very rear frame plate just below the rear radius rod bolt. The front was set at 15 inches measuring to the ground from the rear A-arm mounting tab. The compression knobs on the Walker Evans shocks are set on full soft. For us, the combination of low ride height, great tires and softened suspension put the XP on rails.

We drag-raced this Pro XP 4 against a two-seat Pro XP. The heavier XP 4 was not crazy faster, just clearly the quicker car. That DynoJet horsepower boost shows.


All up, we are really enjoying the XP Pro, the design of the car is certainly upgraded as advertised. It is proving very tough, as it has been run hard (editor’s note: He isn’t kidding. He didn’t get the “Crazy Al” nickname from his wardrobe) every time out. The charge-tube hiccup was just that, and from now on we are just going immediately to the upgraded part. The Dynojet Power Vision re-flash is the cheapest horsepower you can buy at about $400, and the other benefits it offers make it a steal. We will continue to push the envelope on this project, but are satisfied with the direction so far.

Knowles drives hard, so he is picky about tire choices, suspension settings and engine performance. This XP 4 handles great, runs hard and easily stows adventure gear.



Dynojet Research (800) 992-4993, www.dynojet.com

GBC Motorsports www.gbcmotorsports.com

Maxima USA www.maximausa.com

Pro-Armor www.proarmor.com

Raceline Wheels (800) 52-WHEEL, www.racelinewheels.com

Rotopax www.rotopax.com

S&B Filters (800) 358-2639, www.sbfilters.com

Comments are closed, but trackbacks and pingbacks are open.