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QB Valve travel observations

August 11 2010 at 8:52 PM
Cal  (Login CalG)

Just out in the shop having a look at the QB exhaust valve.

Interestingly, the valve stem protrudes through the Inside plug (0200) by .148 in. Seemingly, that would define a possible valve stroke amplitude of the same dimension, with any inertia travel added on.
Once a 12 gm cart (open and spent) is pressed up to the valve body gas entrance the piercing pin stops hard against the cart after only .084 in. of valve stem movement. ONLY 56% of the unrestricted possible movement.

Opening travel and duration may be significantly greater for valves modified to remove the piercing pin.

A second observation: That valve stem must have quite a life being hammered between striker and cart rather than a progressive slowing after being struck open by the action of spring and gas pressure I would expect a significantly shorter open duration.

A significant "tuning" aspect for opening and duration could be the length of the valve head/piercing pin combination. Even with standard springs.
For those retaining cart use any way.

Note that this is a single sample of parts. mfg. tolerance may show alternate numbers, but I believe the trend remains.


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