Any have experience with vacuum pump scavenging?

[SPARKY]

Yes on the piston pins ---that is why I have EDM drilled rods

[1 fast evo 2]

Yes on the piston pins ---that is why I have EDM drilled rods

 How high was the vacuum when you had trouble before you oiled the rods?

[hotrod]

Oiling of con rods  (those with chamfered oil holes in the small end) and piston rings is mostly by oil spray lofted up into the cylinder off of the con rods side clearance. Much of that oil spray is distributed by the air turbulence in the crank case and cylinders as the pistons go up and down. Once you evacuate the crank case to about 11 inches of vacuum the air pumping of the bottom end is drastically reduced so the oil thrown off the rod big end side clearance mostly just goes on a straight line until it runs into something instead of getting churned around by air motion.

Crankcase vacuum also increases the relative pressure of the oil system as it is no longer fighting crank case pressure to escape from the big end bearings side clearance so oil loss through the side clearance tends to increase.

In marginal oil systems that can lead too much oil leaving the big end but it is not getting to the usual places due to lack of air turbulence stirring it around.

As mentioned above your oil pump also now is pulling oil up the pickup tube against the higher suction required due to the lower pressure in the oil pan (in an engine without a vacuum pump crank pressure is often above atmospheric pressure) which would help the oil pump pull oil out of the crank case. Once you start using an evacuated crankcase that assistance provided by blow-by pressurization of the crank case disappears.

The solutions used include diamond hard coated wrist pins and pressure oiled small ends on rifle drilled rods or oil squirters in the crank case to spray oil directly on the wrist pins and piston crowns to both cool and oil them.

Larry

[Rex Schimmer]

Well said Larry! I agree completely. Adding a vacuum pump to a drag motor is one thing but to an endurance motor is a different "kettle of fish". (and any engine that has to run WFO for five miles is an endurance engine in my book!) As Larry has said you need to pay attention to getting lube to the required places and things like DLC (Diamond like coatings) are needed. Again F1 engine development leads the way in developing engines that can live with large amounts of case vacuum. They are running some engines with the con rod directly against the wrist pin using DLC.

Rex

[SPARKY]

"I have EDM drilled rods"--

I do not know what we are pulling vacum wise.

When we went to dry sump after hurting two cranks at b'vill  the  EDM rods were just part of the package from the eng builders experience with BBC boat motors with dry sumps and vacum pumps.

[Kato Engineering]

agreed,
 we experimented with a hard / dry film coating of the wrist pins back in 1987.
 the other option is a ceramic flash coating which is commonplace today.
caution that some of these will wear a common spirolock into nothing.

some of the dry sump suction side locations on the valve spring cover will make the enxt closest rocker and spring not have oil.
a simple baffelplate will help quite a bit.

[SPARKY]

Valve spring oilers have dramatically changed our valve spring life---we went to piston squirters trying to help control piston crown temps primarilly we probalay loose most of the HP gains by putting much more windage oil in play.

[robfrey]

Valve spring oilers have dramatically changed our valve spring life---we went to piston squirters trying to help control piston crown temps primarilly we probalay loose most of the HP gains by putting much more windage oil in play.

Yea, but I think your better off!

[bones]

Hey all
       I'm gunna run a weslake 500 speedway engine . It is designed to be a total loss oil system--The oil just falls out on the track or   
      into a container
     The bottom end is a combination of needle rollers (bigend) balls & roller (mains)
     The oil exits through 2 flapper valves operated by crankcase pressure.
     I have turned the engine from verticle to about 30deg so the outlet holes are not at the bottom.
     
     Would one of these vacuume pumps cope with moving  about 1 qt  of oil in a run.
     I like the electric idea as I wouldn't have to make a drive system fo the pump.
     
      cheers Bones

[SPARKY]

RP harley guys have a small electric pump they run on the salt

[panic]

more pan capacity
Yup. With such big displacement, and the original case volume, the pressure spikes just from piston motion is high. More volume, anywhere it can be hidden, is better, but it's got to be connected directly to the pan/case space (not the valve covers).

Re: pump inlet pressure vs. case vacuum.
By definition, a vacuum system is not vented to ambient. The entire hydraulic system (suction, bypass relief valve, and bearing/tappet/rocker leakage) is vented to the same pressure: the case. The differential between suction and pressure is the same regardless of the starting value.
However: even though the pump delivers exactly the same pressure and volume (but not on a gauge balanced to atmospheric pressure!), as Rex says, the small change in pressure is far more dangerous on the suction side.
Doesn't this suggest that the entire suction side (pick-up head, tube, passage in the pump body, low-press port) should be larger X-section as compensation?

[Rex Schimmer]

Larger cross section on the oil pump inlet certainly helps the pump inlet conditions along with minimum other restrictions, i.e. 90 deg fittings etc. but compared to having the engine case pressure down to 10 or 11 psia these "improvements" really won't do much to improve the pumps inlet conditions. Fortunately most oil pumps are either gear or geroler design which have pretty good suction characteristic but at these low level of inlet pressures they are probably very close to cavatation  and probably are cavating in many situations. When the pump cavatates it will start to pump small air bubbles through the engine and as I remember air is not a good lubricant. I have never thought case vacuum pumps were a good idea for a wet sump engine.

Rex

[robfrey]

Rex,
We typically see about 40hp gains  with our normally aspirated 750 hp small block engines.
I would hate to throw that away.

[panic]

There's an interesting idea on purging the pressure side back to the pan here: http://crank-scrapers.com/Chrysler_slant6_performance%20pump%20mod.html

[Rex Schimmer]

Robfrey,

There is one possible advantage that using a vacuum pump on a wet sump engine that I have never heard discussed and it may be that it is also why the low pressure on the oil pump inlet does not completely cavitate the oil pump to destruction and that is that a low case pressure and elevated oil temps, which reduce oil viscosity, the entrapped air that is in the oil is drawn off by the vacuum. This is very similar to a process, vacuum dehydration, that is used in many hydraulic systems to remove water. All oil has some level of entrapped and dissolved air in it and when the oil is wiped around by things like crank shafts and rods more air is entrapped, it is this air that when it is pulled out of the oil by a pump with a low inlet pressure causes cavitation. It could just be that the case vacuum reduces the amount of entrapped air to a level that reduces or prevents oil pump cavitation. I would require some testing to verify but it certainly has some merit.

Rex