ASK THE MXPERTS: WHY IS ONE CRF450 MUFFLER OPENING SMALLER THAN THE OTHER?

In order to get two exhaust pipes to breathe the same, the right one has to be restricted to allow the left one to catch up.

DOES HANS BRINKER RACE A CRF450?

Dear MXA,

I have a question about my 2017 CRF450. Why does the right exhaust have a smaller muffler hole than the left exhaust?

The simple answer is that with one-into-twoexhaust systems, the exhaust gases always try to take the path of least resistance. That means that the right-side pipe would do all the work unless the Honda engineers rigged the system to equalize the back pressure of the two mufflers. The first step to achieving this in 2018 was to block off the entrance to the right muffler at the Y-juncture. This is achieved with a deflector plate that is welded into the right side of the Y-juncture, at an angle, to redirect exhaust gases to the left muffler.

The second step is to decrease the muffler core size on the right side and increase the core size on the left side (which is why the mufflers have two different size outlets).

The third step is to fine tune the lengths and diameters of the exhaust tubing itself. For example, on the 2019 Honda CRF450, the exhaust features a larger pipe diameter and redesigned layout at the branching location for increased power. The previously 31.8mm diameter exhaust tubing is now 35mm on the right and 43mm on the left. In addition, total tube length (from exhaust port to muffler end) is 98mm on the right and 187mm on the left.

Confused yet? In 2018, Honda solved the one-into-two dilemma on the CRF250 by going to twice pipes, which means two completely separate exhaust ports, exhaust pipes and mufflers. This eliminated the need for the Y-juncture.

 

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