The box on the Max is 7 liters, not bad but ideal
would be 12. CV carbs like to operate in still air. I
agree that a larger box helps respond to an initial
gulp of air that the engine needs when the throttle is
whacked open. However, the pressure will not equalize
if you maintain full throttle. The airbox openings are
too small for top end performance. As a rule of thumb
for high end performance you want an opening at least
equal to the area sum of all the carbs openings.
Sportbike did a ram air test on a a number of
sportbikes awhile back and used a non ram air zrx1100
as a benchmark. They found that the zrx1100 (which has
an airbox set-up similar in size to the Max) went into
a negative 25mb pressure under full throttle. This
means there was a vacuum in the airbox resisting flow
into the engine. This equates to a loss of 3+
horsepower.
My own tests on a homemade flowbench confirmed the
restriction of the airbox...dyno tests show the
biggest difference. Roy Richards jumped 6 hp by
dumping the airbox and going to individual filters.
The same result with open filters may not be the same
at high speed because the disrupted airflow under the
dummy cover but it does illustrate that the Max likes
to breathe...
The problem with opening up the airbox is that it
upsets the pressure differential that the carb slides
rely on to open. The lower the vacuum the harder it is
to raise and properly control the slide rate. The
ideal airbox would have small openings at low rpms to
enable the carb slides to rise quickly and then have a
flapper open at high rpms to better feed the engine.
Several current bikes have this...
cheers, Terry
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