When it comes to adding more power to your ATV, the first thing that usually comes to mind is bolting on a slip-on exhaust. However, that usually means you are also bolting on a lot more noise. HMF doesn’t think that has to be the case.
In our environmentally conscious society, the sound of blaring four-strokes simply isn’t acceptable in many areas. Many public areas require you meet a 93-decibel limit in order to ride. Even some motocross tracks now require you run a quiet exhaust. If you’re fortunate enough to have access to private land, nearby neighbors can ruin a good thing if they take a disliking to the sound of your ATV. If they can’t hear you, there’s nothing to complain about. Performance is still important, but being able to run quiet when necessary is imperative for keeping riding areas open.
With this in mind, HMF designed its Competition Series exhaust systems. The Competition Series exhaust comes in both slip-on and full systems. The exhausts are constructed of stainless steel, with a 6061 T6 aluminum silencer body. HMF’s new flagship sport exhaust system is available exclusively in a powder coated black finish, with polished aluminum end cap.
What makes this system special is its Tri-Max Core design. The system comes with three inserts that can be changed out by simply removing a few hex screws from the silencer’s end cap. The silencer’s three inserts get progressively larger. Installing the smallest and quietest insert is said to restrict sound output from the lower to the mid 90 decibels, while the midsize cap restricts between the mid to upper 90s and the largest insert produces between the upper 90s to lower 100 decibels range. Of course, your sound output will vary somewhat, depending on air density and how long it has been since you repacked your exhaust.
Give it the Gas!
ATV manufacturers have told us that certain fuel-injected models can run with an aftermarket exhaust system without addressing the fuel system. While they may run without blowing up, we haven’t found a machine yet that ran well with an aftermarket pipe. To make the most of the HMF system, it was recommended we add one of HMF’s Fuel Optimizers. They come preprogrammed to work with the HMF exhaust and the airbox lid removed. Unlike some systems that require being plugged into a laptop computer for tuning, HMF’s optimizer can be tuned using the three buttons and eight lights found on the face of the unit.
We recently tried HMF’s slip-on Competition Series exhaust on our Kawasaki KFX450R project quad. The exhaust’s construction looks very good, and we love its modern appearance. We installed the system and fired the machine up before adding the fuel optimizer. Just revving the machine up on the stand it sputtered and popped when we chopped the throttle, an indication that it was running lean. Running lean with the stock fuel system configuration was the first indication that the Competition series exhaust was exhaling significantly more air than stock.
After installing Fuel Optimizer we headed out for our first test ride. The motor pulled notably harder with no popping or backfiring; however, once the quad warmed up it started sputtering and flaring out when we let off the gas. To solve this we increased the amount of fuel fed to the engine from 1.5 to 3.5 on the optimizer’s mode 1 setting, which controls from idle to one-quarter throttle. The motor now idled smoothly and the stalling issue was solved. The tuning procedure is much easier than changing jets on a carbureted machine. Onboard tuning and HMF’s well-written instructions make the procedure simple and unintimidating, even for first-time tuners.
With the air/fuel mixture optimized, we hit the trail and noticed a significant jump in power.
Dialed in and back out on the trail, the exhaust and fuel injection module made a notable increase in power compared to stock. The stealthiest insert wasn’t much louder then stock, although the gain in power was a bit modest. Adding the middle core brought about more power, with a small increase in sound. As expected, running the largest core brought about the biggest increase in both sound and power. How much more power? While we didn’t get to Dyno the machine with the new system, we were able to hit a step-up double, located right out of a corner, a gear higher then we could with the stock exhaust or with the other two cores installed. We could also pull a gear higher out of corners – rarely needing to feather the clutch.
Unless you’re racing on a closed course, you’ll likely use the small or mid-sized insert more often so your sound levels are witihin legal limits.
Stock, the KFX has one of the most user-friendly power deliveries of any machine in the 450 class, It gets into the power and runs smoothly right off idle, builds power smoothly throughout the midrange, and falls off on top. With the Competition Series exhaust and Fuel Optimizer, the power curve felt very similar, but with more power available everywhere, including a small increase in top end. We believe Kawasaki’s restrictive stock air intake system restricts air intake at higher RPM’s, preventing us from getting even more on top. If you aren’t planning on switching out to something like a Fuel Customs intake, the slip on exhaust is all you’ll need. If you plan on swapping out to a different intake system, like the one manufactured by Fuel Customs, you may want to go with the full system, which uses a larger diameter head pipe then stock.
HMF claims that the Competition Series slip-on exhaust adds between 4.8 and 5 horsepower to the KFX. Based on our experience, we would say that is very believable. With the power gains spread throughout the RPMs, we were able to ride faster without working any harder. As a machine we expect to ride on tracks and trails, the benefit of being able to tune sound output without having to swap out exhausts is a huge asset. We feel this system is right for the times, looks good, and performs as advertised.
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