LotusElise wrote: ↑Fri Sep 30, 2022 6:39 am
modok wrote: ↑Fri Sep 30, 2022 3:06 am
Like I've said before.... how do you define... what the throat is?
What part is the throat in this illustration?
Throat is the smallest cross section of the flow path, it defines to a major part how much oxygen can pass per stroke and it is, in most cases, the last chance to accelerate the air to create impulse = mass x velocity before it expands into the chamber. So my point of view of it.
Ok, so to you... throat is MCSA. Fair enough.
IMO if all headporters used drawings we would have advanced a lot faster, clears up a lot of misunderstandings
I've got a 88% throat at the valve seat and a 86% throat slightly upstream in my picture, so, two throats
But anyway, just in my mind the "valve seat throat" is the distance across the 90 degree angle of the valve seat, or at the bottom of the 75 degree if there isn't a 90.
i do agree with David V's book that the valve seat angles do tend to end up very near a radius, not exactly a radius but usually pretty close, and if that is true the valve seat throat% is linked to how tight that radius is. For instance in general a 90% + throat then the radius is too tight and thus you lose flow, or at 85% or less you lose flow because....well, maybe the throat velocity is too high and the air can't make the turn, or I think of it as making the path to the curtain too tight and maybe that's not right, in any case the velocity at high lifts is too high and that does more hurt than the gentler radius helps. but whatever it is... you can find it yourself easy on a flowbench testing valve jobs made of epoxy, and find the same thing he found. Good luck finding anything different but if you do we want to know too.
ONE interesting idea in both these illustrations so far is that this radius does not have to stop at 90 degrees, it can keep going! so then we have like a 105 degree angle upstream of the 90... I would say.
Joe Modello and Kay Sissell and David V all have at ONE time found such a thing improve flow, and so have I, and you might too. But it doesen't always work so maybe situational.
Right near the valve the angles must be concentric to the valve by nature, but as you go farther upstream then less and less so. IMo upstream of the radius of the valve angles it's open season, try whatever.
If you want to accept that the valve seat angles should always be a certain way, always an 88% throat, then you can be more creative elsewhere, decide exactly how to feed that 88% throat most effectively. What heresy!
but hey, maybe, at least an idea to try.
The term -venturi port- has been used to death but in MY mind it means contracting to a smaller size about 1/2 valve diameter upstream of the valve and then expanding out again, what this does is direct the flow at the valve such that the velocity in the center is high but the velocity at the walls is lower. This can allow the flow to go around the radius of the valve seat more efficiently because....., high velocity for the long path following the valve and low velocity for the short path hugging the seat angles. David V's illustration is NOT that, so I think it's not a venturi port, but it is what it is. A venturi port like i described does for sure work, trouble is that it really only works at mid lifts, or at particular lifts. say... with a 88% seat throat and a 86% venturi upstream controlling the airflow onto the back of the valve right you should be able to flow more at .25 lift than if it had just a 86% seat throat, for example. But if looking only at 0.3+ lift(valve size to lift ratio) lift you won't end up with that. but if you focus on .25 or so then it might be the the ticket. And both ways can make power. Look at popular engines, not many are valve limited and use high lifts, does that prove anything? not really, but what is the goal anyway? whatever you want it to be.
Earland Cox years ago did a clean sheet kind of study on ports with slices of tubing, and one thing he found that I thought was very clever was that 'the flow should be aimed at the valve". ok sounds dead simple right? But all real ports are always angled and curved so that can't be maintained at all lifts. The only way for the flow to always be centered on the valve at all lifts was if the port was perfectly straight of course
So depending on how things are, sometimes you can use a smaller area just upstream of the valve to aim the flow at it ideally, and other times you can't, with some designs it becomes impractical. Venturis don't really work around curves.
BTW not aimed at anybody in particular and just what i think about remembering that illustration.