Above: Converting a motocross bike to legal off-road use is easy with the Pro Moto Billet exhaust accessories.
Below: Sacrificing a half-horsepower on a modern 450 is virtually nothing, and definitely worth the benefits.
It’s the wet season and many riders want to get off the motocross tracks and out into the desert or woods for a different type of off-road fun. One of the main problems when heading into public riding areas, and some private ones, is that exhaust systems are usually required to have a USFS-approved spark arrestor. This is especially critical during dry months, but the safety screen is necessary to avoid causing trouble with Mother Nature or The Man regardless of season. Exhaust systems are usually one of the first upgrades, despite the fact that stock units provide plenty of power for most riders. However, aftermarket exhausts are a steep price to pay just to convert motocross bikes into off-road toys.
Pro Moto Billet is an Idaho-based company that manufactures all kinds of aftermarket dirt bike products. One of their popular items is the Spark Arrestor End Cap. This simple product mounts to the end of a stock exhaust muffler and transforms it into a USFS-approved spark-arrested silencer. The end cap is made from anodized 6061 aluminum and is color matched depending on the model of bike. It uses only three bolts to secure to the end of the pipe which makes installation easy enough for the most basic mechanics. It also allows the spark arrestor screen to be removed for closed-course racing, though after testing the PMB cap we don’t feel the need.
In order to test the PMB components, we installed them one at a time and ran the bike on our in-house dyno, followed by a standard 20-inch stationary sound test. Our test unit was a leftover 2008 RM-Z450 purchased new from a local dealer. PMB notes that different models will have slight variances in decibel reduction.
Here are the horsepower, torque and decibel figures for each setup on our ‘08 Suzuki.
|Stock||47.33 HP||32.08 lb-ft||95 dB|
|Spark Arrestor||47.26 HP||32.38 lb-ft||93 dB|
|SA/Silent Insert||47.00 HP||31.97 lb-ft||92 dB|
|SA/Ultra Silent Insert||46.91 HP||31.11 lb-ft||92 dB|
The end cap alone (with screen) dropped our RM-Z two decibels to 93 dB, and this proved to be the best value. Adding the Silent Insert dropped it to 92 dB and the Ultra Silent Insert recorded the same. Our dyno charts shows a 0.42 drop in peak horsepower, much lower than we expected. Monitoring the power curves shows the most effect coming in the low rpm range where all of the components bottled up power slightly. Our test rider didn’t notice a difference out on the trails, but was happy to easily pass tech inspection at our local races.
The PMB end cap makes perfect sense for riders looking to expand their horizons without breaking the bank. Most off-road events or riding areas are concerned as much or more about sound as they are sparks. For under $150 dollars a rider can legally head to the woods and knock off a few of those sport-killing decibels while they’re at it. That’s a lot of bargain in a world sold on high-dollar aftermarket pipes, and something to keep in mind this holiday season.
Spark Arrestor End Cap – $144
Silent Insert – $46.95
Ultra Silent Insert – $46.95