MXA PRODUCT TEST: Yoshimura RS-4 KX450F Exhaust System

WHAT IS IT? A very light and noticeably effective exhaust system for the 2009 Kawasaki KX450F

WHAT’S IT COST? $895.00.

CONTACT?  or (909) 628-4722.

WHAT’S IT DO? Unless you have been living under a rock, you know who Yoshimura is and what product they specialize in. However, it’s what you don’t know that might surprise you. Ever since four-strokes toppled two-strokes in the motocross market, Yoshimura has been sitting pretty. They have never made a two-stroke expansion chamber. The have always been a four-stroke company. Logically, it was a smart decision on Yoshimura’s part to pinpoint Honda CRF250 and CRF450 owners. After all, they sponsor the factory Honda team and are proud of it.

We can’t argue with Yoshimura’s claim that they make top-notch exhaust systems for Honda motocross bikes. We’ve tested the RS-4 system on the CRF250 and CRF450 with great success. Regardless, we thought it wise to show the masses that Yoshimura also makes the highly popular RS-4 exhaust system for other bikes. Not only does Yoshimura produce the RS-4 for a wide variety of models, but we figured that the system would greatly improve any four-stroke motocross bike. We tested our theory on the 2009 Kawasaki KX450F.

WHAT STANDS OUT? Here’s a list of things that stand out with the Yoshimura RS-4 KX450F exhaust system.

   (1) Installation. There was one major issue with installing the Yoshimura exhaust system. The tolerance on the cylinder head flange was off. We had to file the holes in the flange so that the bolts on the cylinder head could accept the flange. Yoshimura has guaranteed us that this problem will be fixed in future production cycles. Aside from that issue, we didn’t have any major problems installing the system.

   (2) Weight. Thanks to a titanium header and lightweight carbon fiber muffler, the RS-4 KX450F exhaust system weighs only 5.75 pounds (two pounds less than the stocker). The KX450F is the heaviest 450 of the Big-Five manufacturers, meaning that a reduction in two pounds is significant.

   (3) Performance. Every MXA test rider, from Novice to Vet to Pro, loved the performance of the Yoshimura RS-4 KX450F exhaust system. The exhaust improved power throughout the entire powerband; most noticeably in the bottom and top end. The Yoshimura system managed to transform the tractor-like KX450F power into engine output that was smooth and crisp.

   (4) Options. We tested the titanium/carbon fiber version of the RS-4, but the system also comes in stainless/aluminum ($595.00) and titanium/titanium ($845.00) versions. If money is tight, we recommend the stainless/aluminum version. It weighs more than the titanium/carbon fiber system that we tested, but is $300 cheaper.

   (5) Place of manufacture. The Yoshimura RS-4 KX450F exhaust system is made in Chino, California.

WHAT’S THE SQUAWK? We had an issue installing the RS-4 exhaust system, but Yoshimura claims to have fixed this problem already.

This pipe is sweet! Every MXA test rider enjoyed the Yoshimura RS-4 KX450F exhaust system. It’s much lighter than stock and greatly improves the power characteristics of the already impressive 2009 KX450F.

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