I'd like a video to show colored mist flowing out of exhaust flange at incremental valve lifts, the same with intakes, only viewing from the opening intake valve in chamber at incremental lifts. Which side or area of the intake valve does the flow favor? Same with exhaust, which side of the exhaust port flange does the flow favor or do the gasses stay in the center of port for the most part? Maybe a clear lexan model of a head & ports would be needed?
I’ve been thinking if I were to set a head on my block, seal that cylinder with a used head gasket, inject a colored liquid of some sort into the cylinder, then pressurize that cylinder with air thru the spark plug hole, then open the valve (checking spring installed) and the air pressure would theoretically push out the dye leaving a trail The intake side might be tougher to do being I’d have to create a vacuum. The only variable if it’s doable is the intake is not in the equation. If anything I think it would be interesting to do, see what happens!
Intake port air flow experiences a two stage process, and especially in a two valve wedge shape open chamber as a factory head has. In terms of a 1.88” intake valve for example up to about .376” lift air passing into the chamber will use the full 360 degree perimeter of the valve to exit around. above this lift point once a larger amounts of air mass is trying to moving thru the port, the air trying to exit the valve on the cylinder wall side finds that side of the bore already saturated with flow, as in restricted because high speed air as we have talked before wants to travel in a straight line along the common wall and exit the common wall side of the valve. Now the air mass as the valve opens further finds far less resistance in the center of the bore and of course on over towards the exh valve side of the bore. Now you would also find that some 65% of the perimeter of the valve is moving most of the air flow thru it, especially once about .500” lift comes around. This is why reworking the valve bowl with a bias to enhance this flow bias effect means so much to making the best use of the valve and valve bowl throat size being employed.
Stevem, When you are testing on your flow bench, how different is the flow when the valve opens then closes and you actually get a pulse flow instead of constant flow? Or, at full throttle is the flow pulse more of a constant with rpm? Reason I ask is most, including you I imagine, check flow at .100, .200, .300, .400, on up lift, etc, and not actual running (open & closing) conditions.
Well first off with a flow bench you can’t open and close the valve when testing while also generating flow numbers you can use. the reason for this is such. If testing at a 28” tall depression as seen on a common 36” tall vertical manometer if you where to close the valve be it a intake or exh valve the fluid column in the manometer would shoot up to the top of the tube and activate the safety valve that keeps the fluid from getting sucked into the interior of the bench and in turn the motors, which is not good as you might imagine! You need a steady depression reading to determine flow numbers. in terms of what takes place within the intake tract let’s take a look. Just keep in mind here that at sea level with a standard temperature and humidity that air pressure is 14.7 psi. This on average is the most pressure you will ever have in a NA motor to drive air thru the carb, down the full length of the intake tract and around the valve into the chamber. With high performance cams during overlap the intake valve is open even before the piston has started it’s way down the bore and the exh valve is open also. At this point in time if the exh system is not well tuned and the engine at a high enough rpm to get that tuning to start taking place ( exh scavenging sucking on the intake port) then all there we have at best is that 14.7 psi trying to drive intake flow into the chamber. Now 14.7 psi is not much especially since the standard factor is stated a 60 degrees and air once in a fully warmed up motors intake tract is far hotter and in turn less dense . Some other factors to keep in mind are these. We flow test these days at 28”, this is equal to a air speed of 350 fps or about 239 mph. A cubic foot of air ( cfm) would then traverse the 1/4 mile in about 4 seconds. 4 bbl carbs are flow rated at 1.5 Hg. 1.5 Hg is equal to a test pressure as seen on a flow bench of 20.4” inches. I am running out of time here this morning for explaining things, but I will pick this up again tomorrow.
