Cylinder Head Porting -
Improving the "Pump"
How many of you
have re-jetted your carbs, and noticed an improvement? Cylinder head
porting will result in an even more noticeable effect, one that you can
feel “in the seat of your pants.”
An engine is
basically a pump. Fuel/air is pumped in, exhaust gas is pumped out.
Increasing the flow rate at which this happens improves the efficiency
of the engine. In fact, the Ural heads are a good design, with one
glaring flaw where the port turns into the combustion chamber (see
pencil in photo).
narrows and the path is angular, creating an area of low pressure. For
example, we have all seen autumn leaves circulate backwards in a pickup
truck bed, instead of flowing smoothly out. Similarly, inside the
cylinder head, some of the fuel/air mixture (or exhaust gas) gets “hung
up”, thereby impeding the overall flow into and out of the combustion
chamber. Removing and blending excess metal to make the path more
uniform in diameter and smoothing out the angles allows for a more
You may be
thinking, “My Ural does all that is asked of it. It goes down the road,
it runs good.” But Ural pilots have developed exceptional throttle
control. On a hill, in fourth gear, we have to throttle back to maintain
speed, or downshift to get rpm’s up. Nobody thinks of his or her Ural as
a performance bike. Yet, at QBall’s annual rally, I was not at all
surprised that improving ride-ability was a hot topic. Porting the heads
is a major step in the right direction.
As a graduate of
the Mondello Tech Center, I can state with confidence that cylinder head
porting should be done by a trained professional, as there are many
factors to be considered. If you ever have the need to remove your
heads, that’s the time to contact a cylinder head porting professional.
Special Thanks to
QBall and Bill of VT Cycles, Poland, ME, for letting me have a set of
old Ural heads to experiment with to demonstrate the extent of the
-Varick T Ross
(Electric Monkey Man)