| [GMCnet] The misconceptions of High Volume Oil Pumps, And Use [message #246236] |
Wed, 02 April 2014 22:03  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
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Rob M put up the site that covered the benefits of oil spray cooling pistons. The information covered on that site is more for very high HP engines. 800 HP at 10,000 RPM's. Yes. We do have that done in our GMC's. But it's a lot less important for us. GM in it's design did make provisions for that. The only time that I install a HV pump is if I add a Turbo charger, or add an oil cooler to a engine that wasn't designed for that options from the factory. As these two items require more oil than the stock pump may be able to. deliver. Our 403's, and 455 engines have a factory bearing clearance on the main, and rod bearings of .0007 to .0027 of an inch. That's less then a human hair. Oil comes out of the mains, rods, and cam bearings. Oil is also delivered to the lifters. That oil is then sent up the pushrods to the valve train that's under the valve covers. The oil spray that has been mentioned that is in the crankcase is the oil that is coming out of the main, rod, and cam
bearings. It ends up in the form of a spray. This spray is vary important in the lubrication of the cam lobes that the lifters ride on. Plus the piston skirts, wrist pins that attach the pistons to the rods, and the piston rings. Some piston cooling is also accomplished be the oil spray. GM did a good job in sizing the stock oil pump to handle the engine requirement along with the oil cooler. There is about one GPM that is forced out of the main, and rod bearings to create that oil spray. GM had an oil pressure requirement of 30 to 45 PSI to accomplish the lubrication, and piston cooling of our engines. This oil pressure is controlled by a relief valve that is in the oil pump that is at the bottom of the oil pan. The oil that comes out of that relief valve can't be used to cool the pistons due to it's location. The only way to increase the amount of oil spray to cool the pistons is to increase the pressure of the oil that is delivered to the bearings. More volume will no
t do it. That can only be done by raising the relief valve discharge pressure. A high volume pump just deliver more oil volume. Not more preasure. So the extra oil put out by the high volume pump will only pump more oil back to the oil pan. This will require about 50% more HP to drive the HV pump. Puts more load on the oil pump drive. And just creates more heat that will need to be cooled back down by your cooling system. Thus there is no real benefit to lubrication or cooling. If you really want to have more spray to cool the pistons. You will have to increase your bearing clearances to allow more oil to go thru your bearings. These engines are low compression, low RPM. and HP. And they don't have a high piston temperature problem any way. Even if you increase the HP, and torque of your stock engine. The stock pump is well within the parameters to do the job required. I'm not saying that anyone is right, or wrong. It's just the pure physics of the engine design. That
s my two cents.
Bob Dunahugh
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