About throat dimensions of a disco valve

[antithesis]

Ok, I finally got the right baker disco valve. I plan to close the stem hole to accomodate a 1/8 poppet stem. If I do this, would there be any potential benefit to filling in the throat space behind the exhaust port, being that it represents dead volume for the air to depressurize into?  In other words making the id 1/8 to as close to the exhaust as possible?

As usual if you need a illustration I'll make one...but the exhaust is very close to the end of the throat where the poppet seats.. anything behind that seems like it would not only stabilize the poppet from lateral motion a little more but also reduce dead volume before the exhaust....

[nervoustrigger]

I agree with your rationale.  I haven’t done an A-B comparison but whenever I alter a valve for a reduced stem diameter, I make the bushing long enough to reach the edge of the exhaust port.  However I haven’t had an instance yet where there was so much wasted volume that I felt compelled to fill it.

[antithesis]

I agree with your rationale.  I haven’t done an A-B comparison but whenever I alter a valve for a reduced stem diameter, I make the bushing long enough to reach the edge of the exhaust port.  However I haven’t had an instance yet where there was so much wasted volume that I felt compelled to fill it.

I'm actually more relieved than anything that you actually understood what I was talking about with my haphazard description 😲

[nervoustrigger]

Yeah it made 100% sense straight away, including the comment about a longer bushing offering better support for the valve.  At some point you tinker with these things enough that you begin looking at every little detail, pretending to be a molecule of air trying to find your way through.  In doing so, you see features that can be improved.  A lot of it ends up being pretty far down on the benefit:effort ratio but when you’re in there making changes anyway, it’s tempting to incorporate little tweaks here and there.

[antithesis]

Yeah it made 100% sense straight away, including the comment about a longer bushing offering better support for the valve.  At some point you tinker with these things enough that you begin looking at every little detail, pretending to be a molecule of air trying to find your way through.  In doing so, you see features that can be improved.  A lot of it ends up being pretty far down on the benefit:effort ratio but when you’re in there making changes anyway, it’s tempting to incorporate little tweaks here and there.

Your philosophy on modding eloquently described my hyper analytical nature about these things to a tee.....you're my kind of guy J😎

[nervoustrigger]

Yes sir, it’s a common disease here on GTA so you are in good company!

[JPSAXNC]

A simple experiment to see the effect of throat/ transfer port volume. Is to load a pellet an inch or two ahead of the breech, and see if there's any difference in velocity compared to loading the pellet right at the breech.

[moorepower]

You have struck up a point that I think is often overlooked, but I think it's more about airflow than volume. I have a mechanical and racing background, and if you have ever seen how to improve flow of air in a cylinder head the port floor is vital with increasing airflow. I see everyone blending the short side radius, while doing nothing with the port floor. Air is slamming into the corner and then air psi is forcing it to go up. A smooth tapered port flow would have to keep up the velocity better and have much improved flow without increasing the size of the port. Some day I will have to make a valve from scratch and test. The Magnum Air vavle is much improved, but it still does not address the port floor as I think it could.

[ped]

if i sleeve a valve down for a smaller dia stem shaft i try to incorporate a valve stem o ring