By Danny Brault

Photos: Danny Brault and Jay Moore

The scream of the two-stroke has been slowly drowned out by the thunder of four-strokes ever since Doug Henry’s win aboard a worksYZF400 at the Las Vegas supercross back in 1997. The following year Yamaha released their production model of the 400 and then in 2001, they introduced its little brother, the YZ 250F. Hit the fast-forward button to 2006, and all five manufacturers will be producing competition four-strokes for the 125 and 250 classes. Sorry, I meant for the MX2 and MX1 classes, or no it’s Motocross Lites and Motocross … well whatever, the point is that four-strokes are now more popular than getting your last name inked across your back.

    The big push to produce four-strokes was due to concerns surrounding emissions. Since four-strokes do not run on a pre-mix of fuel and oil, they produce less exhaust fumes compared to a two-stroke. Technology has advanced quickly and four-strokes are now the majority at the racetrack. However, a new problem has surfaced with the increasing amount of four-strokes on the track: Noise pollution. It may not fill the sky with smog, or infect our waters, but noise pollution does kill motocross tracks and off-road riding areas. Fortunately, Canadian exhaust company, Hindle, has been developing an insert for their mufflers for two years, which may help to solve this noise problem. Racer X Canada, joined by Walton promoter Chris Lee and CMRC’s Brett Lee, made the trip to Hindle’s factory in Port Perry, Ontario to find out how the exhaust company plans to quiet things down at the track.

On the Dyno

Lang Hindle has been working with exhaust systems for nearly four decades, and while his main goal is to add horsepower to a machine, he also takes into consideration the sound it will create. “There have been complaints about noise,” said Hindle. “I read it in all the newspapers. Everybody is saying it and it’s pretty obvious that we have to bring the noise down. It’s motocross events with residents around—that’s the issue we want to address. Also, we want to help out with ATV riders and off-road riders, they’re the kind of people who want to ride but don’t want to disturb the neighbours. So we’re trying to address that, too.”

Through hours and hours of testing in the dyno room, Hindle and his team have come up with the Hindle Noise Reducer, a stainless steel insert that slips into a Hindle Stealth muffler—creating the SuperStealth muffler. Its design forces more sound into the muffler packing and back into the engine; instead of just blowing straight out the pipe to the sensitive neighbors. Okay, reduced volume, that’s great, but what about power? Does less noise mean less HP? That’s what we wanted to find out, so Hindle’s tech guy, Andy Cuttler, set-up two tests for us. First he ran Rob McCullough’s RMZ 450 without a noise reducer—checked the HP—and then ran it with the noise reducer. He completed the same routine with our 2006 YZ 250F test bike. After viewing the results, we were somewhat surprised and impressed. Although the RMZ lost some bottom end power, it still reached the same peak HP. Surprisingly the Yamaha actually worked slightly better with the noise reducer.

Inside the tight confines of the dyno room, it was easy to hear the difference that the noise reducers were making. When the bikes were placed on to the dyno without the insert, and the throttle wide open, the sound was almost deafening and earplugs were worn without question. But when the insert was placed into the muffler, everyone was able to remove their earplugs and the sound from the bikes was much more tolerable. The noise testing was looking positive. Although the dyno charts showed very little HP loss in the Suzuki and none on the Yamaha, and a significant noise reduction, the true test would be outside on the track.

In the Field

With three vehicles carrying bikes, a tricked-out Hindle van, and the Lees, we looked more like Team Honda pulling into a private supercross track than a group of concerned motorcycle enthusiasts searching for a noise solution.

    Our test format was simple: First each rider spun a few laps without a noise reducer, then a few laps with it installed. From a rider’s perspective, we wanted to find out what the bike felt like on the track and whether the noise reducer robbed power. Our second objective was to evaluate the change in sound, not just with the decibel meter, but also by our ears and how the sound resonated.

    The general response from riders after testing the RMZ 450 and YZ 250F with a noise reducer was that there was some loss of bottom end power, the bike was slower revving, and it felt a little sluggish. However, this could easily be confused with sound, since the bike wasn’t revving as high, riders may have confused this with power loss. So to find out if the bike was actually slower with the noise reducer installed, McCullough began recording Jay Burke’s lap times when he rode the 250F with and without the insert. Much to our surprise, and contradicting all of the riders’ observations, Burke was actually spinning quicker lap times with the Hindle Noise Reducer. How could this be? Well, one factor is that the Port Perry track was hard-packed and since the power comes on smoother with the noise reducer, Burke said it was easier to roll around the flat corners. McCullough also suggested that because the bike is quieter, that means less energy is transferred to the rider. We were happy with the results from the riding tests, but that was secondary to the real issue that is responsible for shutting down tracks—noise travel.

Lang and Cuttler stood close to the track with a decibel meter throughout all of the testing and recorded the sound from the bikes with and without the noise reducer. The noise reducer was lowering the dB level, but it varied from rider to rider. “It’s about a good two dBs within the 90 range,” said Hindle. “We’re pushing around 97 without it and 94 with it. In some cases it’s more than two dBs, but it’s inconsistent with how riders get on the throttle.”

As riders took turns running the noise reducers, everyone else listened. Again, we received a positive result. The group’s consensus was that the noise reducer muffled the sound of the four-strokes, making them sound similar to an XR or a TTR 250, and when the bikes were ridden at the far end of the track, the noise wasn’t traveling nearly as far. Barry Heatherington, the track owner, even commented that the YZ 250F had a softer sound and was quieter than a 125. Hindle was pleased as well with the testing. “I think it’s very good. It’s what we wanted to accomplish: To make a nice, pleasing sound that doesn’t travel, that still has an exciting sound to it but not an offensive and traveling sound,” said Hindle.

What Did We Learn?

Hindle deserves a big pat on the back. Not only did they develop something that lowers the dB level of a four-stroke and reduces noise travel, they did it without comprising power. Many riders are under the false illusion that sound equals horsepower, but now that Hindle has drawn up the blinds, we can see that a quiet bike can be a fast bike. Brett Lee has even suggested using a contingency plan between CMRC and Hindle. “It’s just an idea, but we’ve discussed an incentive program with Hindle,” said Lee. “If people are using Hindle Noise Reducers than they may receive discounts on entry fees.”

    We cannot ignore the noise problem any longer. Noise may be the death of our sport, and as riders, sanctioning bodies, manufacturers—everybody—we need to band together to fix this issue because we’re not gaining tracks, we’re losing them.

There were a lot of people involved with this project and Racer X Canada appreciates everyone’s efforts. A big thank you to Barry Heatherington for allowing us to use his track in Port Perry. Thanks to the Hindle crew—Lang, his son Lee and daughter Alison and our mechanic for the day, Andy Cuttler. Thanks to the riders who tested the noise reducers, and to Chris and Brett Lee for helping out. Oh and of course, Racer X Canada's test dummy Rob McCullough. Even with two broken legs, he still ran all over the countryside picking up bikes and tires and organized this whole event. Thanks Rob. For more information on Hindle pipes, visit www.hindle.com.