Get (or modify yours) collectors with evac bungs, pipe and a couple Thermactor anti-backfire valves and have at it....
I have an "automatic" pressure relief valve. If I exceed 6,000 rpm or so, the pressure pops my dipstick up about 2 inches.It seems that at some level of increased performance, the original PCV valve spec does not flow enough air to relieve the crankcase of pressure.
Well, I never said that, and a draft tube will flow as much as much as atmospheric pressure will allow to be spit out a 5/8 or so inch ID pipe... The benefit of a PCV system is two-fold.... one, the gases are evacuated from the crankcase under suction, for 99% of the time when vacuum is present and, two, redirected into the combustion chamber to be burned vs. puked out into the atmosphere as a pollutant or puked out onto the ground.Ok, I'm stupid. Why won't a road tube flow enough pressure?
Well, actually there is. At WOT vacuum is low, but not absent. Bernoulli says that a low vacuum velocity is high and, at low vacuum, the PCV valve is wide open. Therefore you're going to move a fair amount (in volume) of crankcase vapors as opposed to when the throttle (and PCV) are near closed.Of course, during "non-typical" driving, e.g. WOT (=typical for ArizonaGT as I understand it ), there's no vacuum evacuation, since there's (almost) no vacuum at the source (the intake manifold plenum) and the ventilation just bleeds of the pressure.
Bernoulli's Law applies whichever way you want to state that vacuum is inversely proportional to velocity. Air has mass so if you're moving 100 cfm of air at a pressure differential of 2"hg that's moving more air than if you moved 50 cfm at 4"hg. Also bear in mind how much pressure you need to build in the crankcase to cause oil, which isn't under any other pressure, to leak.Sure, there is some vacuum, but very little, unless the carb is too small. And yes, the PCV valve opens up to compensate. But the discussion was about a reduction in leaks if the PCV system keeps the crankcase pressure below atmospheric. My comment to that was that at WOT there will be very little vacuum in the manifold and even less in the crankcase and thus the influence on leakage will also be very small. Especially considering the blowby will be higher due to the high cylinder pressures (even though the relative loss of the charge doesn't necessarily have to be worse)
BTW: Bernoulli says that pressure is reduced when velocity goes up.
The annular discharge booster doesn't increase airflow velocity any more than a straight-leg or down-leg booster of the same dimensions. The difference is in the multiple, small discharge holes around the inner part of the venturi that produces better fuel atomization than the other types. As far as vacuum at the "suction holes"... Don't confuse manifold vacuum, created by the movement of the pistons within the cylinders, with the venturi effect. They are two different "animals". One is responsible for drawing a fuel/air mixture into the cylinders, through the intake valves. The other is the pressure differential created by slowing down airflow using a restriction and using that differential to siphon fuel from a reservoir (float bowl). They are, for all intents and purposes, independent of one another as a large volume of air passing through the intake manifold and into the cylinders may result in a low manifold vacuum because there is low restriction (throttle plates open) that same flow of air passing through the restriction of the venturi will cause a large pressure differential from atmospheric pressure. Remember that the air does not remain restricted...after passing through the venturi the space widens and the air, once again, slows down.I think this is more an "argument" about definition than about physics. Out of curiousity, when I would install an annular booster in a carburator that increases the air flow velocity through it, would you say that the vacuum at the suction hole(s) to the jets has gone up or down (i.e. more or less vacuum)
LOL. One last shot....OK, the annular booster was not the best example. How about an airplane wing: speed up the air on the top side, pressure on the top goes down, wing goes up.
About the rest, I know all that. But the discussion was about vacuum in the crankcase and how that helped with reducing oil leaks. I then said that effect will be very low at WOT, because there's very little manifold vacuum at WOT. Then you brought in the Bernoulli effect but in my opinion you mixed up high and low vacuum and how it correlates to air velocity.
But let's not dillute this topic any more with this side discussion
Yes. The speed of the air, in feet per minute, times the volume of the air, in cubic feet, is going to equal "CFM" or Cubic Feet per Minute.OK, I will respect the topic starter's wishes and will reluctantly resist the urge to fire back
One last question though, just because I wonder what you mean:
What velocity do you mean, of the air flow through the throttle bores?
If their wings ain't flappin' it's 32 feet per second, per second....Come on guys, we all know the only really important question is, "What is the air speed velocity of an unladen swallow?"
"About two and a half pounds".But how much does a hen way ?
Yes, you are absolutely correct! I should have said the flow area, in square feet. On the other hand, any air passing over an orifice is going to induce a low pressure area. Think sandblaster gun or siphon-cup paint sprayer.Well then, since Woodchuck enjoys it so much
Strictly speaking, speed of air [ft/min] x volume of air [cubic feet] = something in [ft^4/min] but I'm sure you meant speed of air [ft/min] x flow area [sq ft] = volume flow [CFM]
The flow through the PCV valve is a function of the flow area and the pressure difference over the valve. A high air flow velocity through the carb and manifold does not necessarily create a low pressure at the PCV valve exit. Unless it is positioned in a low pressure wake area, which is possible.
I know, hence the "wise ass" comment
‘Drain back’ catch can… Ive never used (or seen) that 🤷