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Breather Check Valves
Back when I was writing
tech articles for Battle2win magazine, I did an
article on these breather check valves you see
advertised for HD motors. Sold under the names "Krank
Vent" "Krank Vent Plus", "Power Vent", and various
other names, they either promise or in some cases
highly suggest that using them will add power to
your motor.
I understand where
they're coming from. An HD motor has a variable
volume crankcase. Unlike most car motors, which have
a piston going down for every piston going up, the
volume of the HD crankcase changes due to the 45
degree common crankpin design. It stands to reason
that check valve on the crankcase vent could cause a
vacuum to get pulled on the upstroke of the pistons,
potentially helping ring seal. Dry sump oil pumps
that can pull a vacuum when used in conjunction with
low tension oil rings are a well known technology in
the circle track car racing world.
What I couldn't
understand was how these things could bring anything
to the party considering the bikes already have a
check valve in line with the breathers (the umbrella
valves). Unless of course those valves were
defective. But then it seemed like the marketing
around these check valves must be based on the
notion that the valve you already have is defective?
That didn't make much sense.
So anyway, I went off to
dyno test these things and see if I could
substantiate any of the claims, blatant or subtle as
they might be. Spent hours messing with the Hayden
and Spyke brand devices. Here's what I came up with:
Open is just that,
vented to the atmosphere with no additional valves,
other than the factory umbrella valves which were in
place at all times.
"Kuryakyn" refers to the
little Kuryakyn adapter I used to route the blow-by
back into the carb.
"Spyke" and "Hayden" are
the best pulls with these respective devices in
place.
Just for kicks, I
blocked the vents and did some pulls, "closed" is
the best of those results.
As you can see, the only
thing that really mattered was whether or not the
blow-by was being recycled back into the engine.
Recycling the blow-by, the way the factory does,
costed a little power over a wide range. Other than
that, the motor largely ignored what I was doing
with the breathers, at least from a power point of
view.
When this result was
published in Battle2win, I got quite the reaction
from ET products, makers of the Spyke device. A
dialogue ensued and I tried to pin him down on my
basic question, i.e. how does putting a check valve
downstream from the factory check valve change a
thing? But I never got a real answer. He did claim
though that the Spyke device was effective at
improving power, even though he never explained how.
Anyway, in the interest
of fairness, and just because I really wanted to be
sure of myself, I did a whole bunch more testing of
the Spyke device in particular on other bikes. Here
are the results of that testing.
Dyno's are not a 100%
repeatable measurement tool, you instead get a range
of results in any given configuration. So I'm
showing the range rather than a specific result for
each:
1999
Buell M2
Here are all the
baseline pulls on my '99 M2, no breather check valve
in place other than the factory umbrella valves, and
vented to the atmosphere. The power varies from 84.3
to 85.4.
Here are all the
pulls I did on the same bike, same day, with the
Spyke device in place. The power varies from 83.5 up
to 84.8.
Blue: With Spyke Device
Red: Without Spyke device
And of course, this the best pull from each
configuration, overlaid onto the same chart. Yeah, I
know, it *looks* like the bike ran a tad better
without the device, but it didn't, this is normal
variation. I guarantee you if I did enough pulls
with the device, and played the heat soak just
right, I could've equaled the other results. This is
a tie.
1996 Buell S2
Here are all the
baseline pulls on my '96 S2. The power varies from
85.9 up to 87.1
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