WHAT IS IT? The FMF 4.1 RCT Honda CRF450 single-sided exhaust replaces Honda’s 2017-2018 twin-pipe design with a more traditional single exhaust.

WHAT’S IT COST? $874.99 (Titanium/ Ti canister/carbon fiber exhaust tip), $774.99 (stainless steel/aluminum canister/carbon fiber exhaust tip).

CONTACT? or (310) 631-4363.

WHAT STANDS OUT? Here’s a list of things that stand out with the FMF 4.1 RCT single-sided exhaust system for the 2017–2018 Honda CRF450.

The aluminum cantilever brace supports the single muffler.

(1) Installation. Removing the stock twin-exhaust system from the CRF450 requires about 30 percent more work than a typical motocross exhaust system; however, there are few easy-to-remove exhaust systems made today. The CRF450 has twin pipes. The YZ450F has a wraparound head pipe, and the 450SXF and FC450 exhausts cannot be removed without taking the shock off the bike. That only leaves the KX450F and RM-Z450 exhausts. Once we had the twin pipe off, we had to mount the special aluminum cantilever brace that is required to support the single muffler. Honda’s twin mufflers are mounted far forward, so the only bolt hole for the single muffler is too far forward to support the muffler by itself. The cantilever brace offers a second mounting hole. We used the stock Honda bolt up front and the supplied longer bolt in the back.

(2) Stock trim. The stock 2018 CRF450’s engine makes 57.99 horsepower at 9600 rpm. The CRF450 powerband is herky-jerky from low to mid and doesn’t like to pull a tall gear. It is at its best in the midrange.

(3) FMF performance. MXA gets more requests for information about singe-sided CRF450 exhausts than any other pipe. FMF didn’t make one for the 2017 CRF450 but decided to start up production again for both the 2017 and 2018 CRF450s. How did it run? We were shocked. The single produced 2 horsepower more at 5000 rpm. This would not be significant on a normal bike, because 5000 rpm is fairly low on the powerband, but since the 2017–2018 CRF450 has issues down low with throttle response, the stronger FMF low-end smoothed out the jerky feel. From 7000 rpm through 9000 rpm, the single and twin were a matched pair, but as the rpm climbed, the single took off. It made 2 horsepower more at peak and 3-1/2 horsepower more by sign-off. As an additional bonus, it revved through the power faster, getting to the meat of the powerband quicker. The FMF single-sided exhaust connected the bottom and mid, making the CRF450 easier to ride.

(4) Weight. The FMF 4.1 RCT single exhaust is only available in stainless steel with a Ti canister and carbon fiber end cap. If there was a titanium model, it would be 3 pounds lighter, but the stainless steel head pipe and cantilever brace keep the weight savings at 2 pounds.

(5) Price. Our FMF single was the first pre-pro version, so the prices aren’t set in stone, but the previous single (for the 2016-and-earlier twin-pipe CRF450) retailed for $699.99. The stainless steel CRF450 twin exhaust retails for $999.99 and titanium twin exhaust system is $1295.95.

WHAT’S THE SQUAWK? No complaints.

MXA RATING: What’s there to think about? It costs less, weighs less, is less prone to damage and makes more horsepower. This is a no-brainer.

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