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Can someone explain what the difference is between high volume and high pressure? My old pump was HV.
If you've got a garden hose the flows 3GPM and you want 5GPM you are asking for a volume increase if you open the valve up more to increase volume well guess what you also increase pressure.
THe same would be true if you wanted more pressure you also a going to end up with more volume because we cant change the size of the opening of the garden hose (Bearing clearance in this case) so by forcing more oil through the same size hole you get more pressure.
The only way I can think of increasing volume without building pressure is if the garden hose was running really slow and only half the hose was filled with water so it was more like a canal. If you increased volume just a bit so it did not fill the hose that would probably get you more volume at the same pressure. I would think this is not the case in the oil system
It has to do with the oil system design and bearing clearance. a HP pump can deliver high PSI if the system doesn't have a lot of volume (stock style) but the HP pump might not work if you've enlarged any of the oil passages or opened up clearances. A HV pump will provide more volume for a modified system than needs more oil to keep up the pressure needed for a good ol wedge at the bearings. so using a HV pump on a system without a lot of volume raises pressure too high, and makes the pump work a lot harder.
Last edited by racer_dave; 02-05-2017 at 01:43 PM.
The pump difference is in the fit (clearance)of the gears in the pump and the size of the gears. These pumps are constant volume pumps, that is one rotation of the shaft puts out a fixed amount of oil whether it is going fast or slow.
A high pressure pump will have very tight clearances. Being a gear pump with an inner star shaped rotor running in an outer star shaped cavity, the tighter the fit the higher the pressure but the less the volume per revolution for a given thickness pump. The pressure is generated between the tooth and the cavity the inner gear run in. The closer the teeth the higher the pressure.
For high volume you need to have a bigger cavity. The bigger the cavity the more oil per rotation. You get a bigger cavity by making the gears thicker or not come as close together. If you run a high volume in a restricted oil system, the pump will have to work much harder because the pump wants to put out the same amount of oil every revolution but the only way to put more oil through the restricted system is to generate more pressure.
If at idle you put a quart per minute through your oil system at 30 psi (numbers are just for demonstration) at 2000 rpm the pump will try to put 2 quarts through it. The oil pressure relief valve in the oil system will bleed the extra oil back to the tank, once the it reaches pressure, but the pump still tries to push the oil out. A high pressure pump with small volume will require less energy (torque) to drive the pump. A high volume pump will try to build the pressure but because it is trying to pump more oil it will take more energy. The resistance is in the pipe to the pressure relief valve and engine fit. If the engine and bearing fits are open, then the high pressure pump may not deliver enough oil to ever get the relief valve to open, so you would need a high volume pump.
Seems like its all sunshine and bunnies for the most part. The oil pump makes 35 to 37 normal operating temp at idle and just about sixty above 4,000. This is good. Cold it doesnt go over 60 either thanks to the more conservative relief valve. So Im not making 85 psi when cold now so thats good news for the cam and dizzy gear.
The only issue now is that stupid roll pin on the dizy gear. The carbon composite gear fits on their with only moderate effort (not the 1,500 pounds like with the steel gears) it could be tapped onto the shaft with a hammer.
I set the timing to 11 adv and the idle seemed low after driving it around. checked timing and it was like -0 so I set it back to 12 and made sure i got it right and its tight Its possible I didn't set the timing proper when I pulled the dizzy out to check the wear pattern Im hoping its that and not a roll pin bending...Ill know once I drive it again.
The gear looks like its possibly sitting too low on the shaft...The face maybe dragging on the bushing inside the block that supports the end of the dizzy shaft..I do have end play so its not totally bottomed out but the wear pattern looks high on the teeth as well.
The below photo is a picture of the mesh...not sure how useful that is but **** it I was there so I took it.
Well so far I have just over 225 miles on it since the rebuild. I drove it around town and it seemed fine. The backlash between cam and dizzy gear was about 002 almost nothing. after 10 or 20 miles it was about .008. I was like **** it and drove it to the Wold Ag Expo and back and around town to work a bunch and the backlash is still about .008 im hoping it stays like that for a long time.
I pulled it out and took a look seems fine, Put marking compound on it for fun and got the below contact pattern. Seems consistent all the way around
02-04-2017, 10:36 AM
