combative hodaka
Member
Whoever comes up with an answer ( legit ) to this question needs to apply imediatly to all cam grinders on the planet.
Purely hypothetical.
- Thread starter ABR #69
- Start date
I realize this is an old thread, but it deserves more discussion.
In an ideal world, this is just an air admittance valve question. Assume the piston during downward motion creates a perfect seal in the bore and creates an ideal vacuum.
Your valve would stay closed so long as your valve spring had the ability to apply 14.7 psi (or whatever your local ambient air pressure is) across your port cross section behind the valve.
For a camless setup, you'd need to be able to reference MAP and create a way to hold the valve closed with the same amount of pressure - this would also create a system that could be boosted and would automatically increase the valve pop-open pressure.
My main question would be as the intake valve closes, does the air column behind the valve have enough momentum to lift the valve off the seat if you're running right at ambient pressure for seat pressure.
In an ideal world, this is just an air admittance valve question. Assume the piston during downward motion creates a perfect seal in the bore and creates an ideal vacuum.
Your valve would stay closed so long as your valve spring had the ability to apply 14.7 psi (or whatever your local ambient air pressure is) across your port cross section behind the valve.
For a camless setup, you'd need to be able to reference MAP and create a way to hold the valve closed with the same amount of pressure - this would also create a system that could be boosted and would automatically increase the valve pop-open pressure.
My main question would be as the intake valve closes, does the air column behind the valve have enough momentum to lift the valve off the seat if you're running right at ambient pressure for seat pressure.
direct air injection. Cam only for exhaust and not like we use now something totally different as far as the valve. Food for thoughtWhile intake valve closing is the most important timing event controlled by the camshaft, the loss of valve train control resulting in reversal of flow into the intake tract is what gives the characteristic valve float loss of power.
If the valve seals when cylinder pressure is greater than incoming air pressure, no reversal can occur.
Usually, the weight of the valvetrain and harmonics in the valve spring overcomes the increasing cylinder pressure to allow this reversal.
Here is a link to a video showing what these harmonics look like.
https://4cycle.com/karting/threads/valve-spring-motions.123995/
If the valve seal were not dependent on the spring to control the weight of the components, then there would be no such thing as valve float. As long as the weight of the column of air was adding to the cylinder, no harm is done.
Shop air compressors use this principle.
ABR #69
Member
The more I've researched the entire process, the hardest part is controlling the valve closing. Without a solid cam, and proper valves springs to keep the valve in contact with the cam. The valves will slam closed, and that creates many issues as most of you know. The power needed to control the valves at this point is quite incredible.
(Edit) And when I mean incredible, the amount of white papers published on this very issue is fairly interesting. No one has been able to control "well" besides two groups, and the amount of money they spent in doing so is absolutely staggering.
(Edit) And when I mean incredible, the amount of white papers published on this very issue is fairly interesting. No one has been able to control "well" besides two groups, and the amount of money they spent in doing so is absolutely staggering.