WHAT IT IS:
FMF’s Powercore 4 slip-on for the Polaris RZR XP 900 is a compact, lightweight dual exhaust that replaces the bulky, single-outlet, stock muffler. It’s made of durable, stylish stainless steel and incorporates re-packable mufflers so it’s easy to maintain the system’s performance, sound quality and sound level. The FMF exhaust also accepts FMF’s low-restriction spark arrestors. This is an entirely new exhaust design, so new that FMF hadn’t settled on a retail price when we went to press. FMF’s exhausts are always priced competitively, so we expect this dual slip-on’s price to be in line with similar systems from other leading performance-parts manufacturers, which is around the $475 mark.
For durability, FMF’s Powercore 4 dual slip-on for the XP 900 uses all the stock system’s mounts, both rubber-isolated muffler hangers, two spring muffler brackets, two spring mid-pipe to header brackets and two rubber-damped locating pins. The stock muffler’s locating pins are simple, stamped-steel pads that can buzz and squeak. The Powercore 4’s collector/mid-pipe uses the stock cone-type head pipe to mid-pipe mount and gasket and a precise slip-fit to the dual mufflers. The slip-fit union requires no gaskets or clamps and provides a bit of flex that helps the system resist vibration and heat stress.
The entire muffler is held by strong springs, so all you’ll need to remove the stock part and install the FMF slip-on is a sturdy spring puller—and we mean sturdy. We went rolling backwards in the dirt out at the test site when our regular spring tool let go. We didn’t have time to order the slick, solid-steel spring puller FMF sells, so we came back at it with a homemade puller, a thick-steel S-hook from a truck bungee cord clamped by a big pair of vise grips. With the springs conquered, the FMF pipe went on easier than the stocker. With care, you should have no trouble reusing the head-pipe-to-mid-pipe gasket.
We used a completely stock 2013 RZR XP 900 Walker Evans LE to test the FMF Powercore 4 slip-on. We tested the stock exhaust and the FMF pipe back to back on the same cross-country loop on the same day to keep course and weather conditions consistent. Because it was 100 to 105 degrees at 2600 feet, FMF’s tech support said the stock EFI settings would work fine, and they did. At lower elevations, especially in cooler temperatures, you’ll want to remap the EFI.
As anyone who has driven an XP 900 with the stock exhaust will tell you, the machine runs strong and has excellent throttle response. It’s also amazingly quiet, which is a great thing, especially if you ride where sound can be an issue.
With the FMF Powercore 4, the 900 runs stronger, build revs quicker and has excellent throttle response, but at 100 dB, it is not quiet. From the moment the machine fires, and the deep, sharp, solid beat of the exhaust begins, there’s no question the Polaris is breathing freely. With the slip-on, the 900 pulls harder off the bottom, more solidly in the midrange, and it rushes through to top revs more quickly. As much as we like the extra punch, the snarl of this exhaust and the sweet bellow it makes on deceleration, it’s best used fully open only for racing or in the company of motorsports enthusiasts. For trail riding, we strongly recommend running FMF’s 96 dB quiet cores with spark arrestors. They’re $40 each.
Nothing upgrades the looks, sound and performance of a machine all at once like a good performance exhaust, and FMF’s Powercore 4 is very good, though the sound level is too rowdy for anything but racing with the straight-through silencers open. Since FMF is one of the most respected makers of quiet-performance pipes, we hope they’ll label the open version of this exhaust for racing only.
One of the best things about slip-on systems like this is that they produce most of the performance gains of full systems, often for just a little more than half the price of full exhausts, including head pipes, which leaves lots of savings for quiet-core/spark-arrestor inserts. Slip-ons are also simpler to install than full systems, and the Powercore 4 for the RZR is actually easier to work with than the well-designed stock muffler. At 10.7 pounds, it’s also more than 5 pounds lighter than the truck-size, 15.9-pound stock muffler.