What is the generally accepted flow rate and pressure differential for vacuum pumps?
Originally, I heard no more than 15" Hg but the PS bikes are running ~22" Hg or so.
I know that the pressure differential affects the oil pressure and has an effect on wrist pin lubrication and I can deal with these issues.
I've also heard from PS bike guys that too much flow slows them down.
Additionally, I heard that PS car guys are running electric pumps to suppliment the dry sump systems.
Are there any other negatives to running higher pressure differentials?
Does the flow rate depend on crankcase volume, CFM of blowby, or none of these?
How does a vacuum pump affect the number (or need for) of gas ports in the piston?
What is the theory on ring end gaps and ring tension as related to the pump?
It's been recommended that I should run the second ring end gap at 0.040" to 0.050" and run the lowest tension rings that I can get away with as long as there is no "smoke" when going down the track.
I would like to get input from those who have experimented with vacuum pumps.
When responding please differentiate between facts and opinions.
Thanks,
Vacuum Pumps. Ring End Gap, and Gas Ports
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The only thing high crankcase vacuum should cause oiling problems with is whatever is lubricated by splashing oil and windage. With a less dense air inside the crankcase the oil isn't carried as easily by the air movement. Thats why wrist-pins are first to have trouble. I think Nascar uses oiling holes thru the rod to the pin. Coated pins are also common now to help this problem.
The tighter you can get your engine the more vacuum you can achieve with less pump or pump speed. Bad ring seal will make it hard to make 10"Hg. Gaskets and seals also become an issue as the vacuum increases.
Rick
ps. It is my opinion that these are facts
The tighter you can get your engine the more vacuum you can achieve with less pump or pump speed. Bad ring seal will make it hard to make 10"Hg. Gaskets and seals also become an issue as the vacuum increases.
Rick
ps. It is my opinion that these are facts
We experimented with different vacuum levels in a well sealed wet sump sbc and found that we had pin galling with vacuum over about 15” and that this went away with vacuum in the 10” – 12” range. We did see reduced oil pressures with increased vacuum (about 3-5 psi with an increase from 10” to 16” vacuum), but this didn’t seem to have any adverse effect on the motor and changing from a 5/8” pickup to a 3/4” pickup on the oil pump seemed to correct most of this.
IMO, the reason for running pan vacuum is to reduce friction by allowing the use of low tension rings without losing ring seal. Gas ports contribute to the same reduced friction by allowing the use of reduced radial width top rings. Then the gas ports provide the needed “tension” during the power stroke and the rings get a free ride during the other 3 strokes.
The capacity of the pump, how hard you turn the pump, the size of the motor, how well the motor is sealed and how much blow by you have all contribute to the vacuum level that you can achieve in any given application.
IMO, the reason for running pan vacuum is to reduce friction by allowing the use of low tension rings without losing ring seal. Gas ports contribute to the same reduced friction by allowing the use of reduced radial width top rings. Then the gas ports provide the needed “tension” during the power stroke and the rings get a free ride during the other 3 strokes.
The capacity of the pump, how hard you turn the pump, the size of the motor, how well the motor is sealed and how much blow by you have all contribute to the vacuum level that you can achieve in any given application.