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Originally Posted by Ultramaroon
I've read here that shimming the spring makes no difference. Also, with your mode of operation, especially considering the flow rate of the pump, it should compensate for viscosity (temp). It doesn't seem to.
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A shim doesn't do much. If you over-shim, it can actually cause pressure to be excessive and split the inner pump gear. I've heard of shims also causing premature bypass valve spring fatigue (from over compression). IMO, a shim is not beneficial beyond marginal.
Subaru oil pump are unusual in the car world in that they have WAY more flow than is necessary 95% of the time. There are V8 engines that don't have nearly as much oil flow capacity as a Suby pump. They've always been this way, and yet, they have (by design) poor rod bearing oiling and marginal main oiling
Here's a plot comparing the same pump with 2 shims added...
Quote:
Originally Posted by Petah78
Sorry to be a noob but i am trying to understand. Are you suggesting that the dimensions of the pickup tube is limited oil flow of 2gal/min? Meaning that is the max that the engine is getting regardless how hard the oil is pumping? But if it's partially blocked, wouldn't that metric, 2gal/min be even lower?
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Don't apologize, we've all been there!
No, not at all. From our testing the pickup is very little of a restriction when you look at the system as a whole. Can you pick up a couple psi and small % of flow by installing a performance high flow version, sure you can. Anytime you reduce a restriction on a pump's inlet, it becomes more efficient.
The systems flow limitations is really down to the engine's lubrication design: engine's clearances, and other things like AVCS, oil feed, etc... Those are all restrictive. The best way to improve oiling system performance is not by shimming or adding a bigger pump, it's rebuilding the engine with making modifications to the oiling system to improve its performance. One of the things we learned for example, is ALL engines (new used or otherwise) get a line bore (not a line hone). Once true, we actually close the main clearances below factory spec at ~.0007 +/-.0001. This smaller main clearance forces more oil to the rod bearings (the weak link). We've done this for stock engines running 0w20 to 760whp running 20w-60. We always run stock unshimmed pumps regardless or redline RPM or power level and have not had an oiling related failure in at least 10 years.