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Old 04-23-2013, 08:36 PM   #3 (permalink)
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Originally Posted by renault_megane_dci View Post
So that is like Yamaha EXXUP system ?

It is just a matter of linking the exhaust flow with the inlet flow (AKA throttle) to get rid of a part of the camminess of those very high specific power engines.
I believe they can do the same with cam phasers these days but the trend might not have reached the bike world so far.
I believe the EXUP was simply a butterfly valve that created restriction at lower revs. This HTEV is more complex and, well, seems like it should work well.

IDLE to 3000 RPM:
Cylinders 1 & 2 are combined, cylinders 3 & 4 are combined in HTEV with only two outlets for back pressure:

3000 to 8000 RPM:
Flow straight through the HTEV. Cylinders 1 & 4 are combined, cylinders 2 & 3 are combined in the exhaust collector after HTEV (not pictured):

8000 RPM + (11500 RPM Redline):
Hard to tell by picture but it looks like all cylinders are combined in HTEV:

Honda has used actual for real VTEC in two bikes - the Japanese only CB400SF and VFR800F. Critics say the only thing it accomplished was added complexity. I rode a VFR800 version and it was kind of neat, but whether it was only the sound change at 6800 RPM that tricked my head or not I will never know. Not sure why it hasn't caught on - more expensive? Heavier? Higher chance of catastrophic failure if something goes off? Who knows.
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