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).

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 The opening 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 efficient engine.

 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.

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 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 possible improvement.

 -Varick T Ross (Electric Monkey Man)


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