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It seems to me the functionality of a windage tray/crank scraper was directly related to rpm? That is, at 5k-6K rpm there's this huge wad of oil spinning around with the crank, causing major parasitic drag [you know, like a politician?]. At the lower diesel rpm's the usefulness is somewhat doubtful, but not to say it wouldn't help a wee bit, just not that much compared to a high reving gasser.
 

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Yeah, all my info is from Hi-Perf Dodges or Mopars. On engines that really spin up, like a 383 hi-po that can turn an easy 8,500 rpm it's a major improvement. Not a lot of help on a Slant Six 1bbl....

There's at least 2 different types, one a baffle that covers the whole top of pan and bottom of crank, with louvers in it for drain back, and another that's more similar to a blade scraper. The blade scraper has to be pretty stout steel because of the torque of spinning oil blob. I think the single wide one with louvers is the best bet.
 

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Yeah, and a lot of guys have taken it even farther: knife edging the crank journals so they cut through the oil more easily. Actually that crank profile's not what causes the phenomenon. It's more like occlusion, where the spinning mass sucks up the oil, rather than it sticking to crank to form a progressively bigger glob.

Always important to consider what function splash oiling plays in a particular engine, regarding the lubrication of lower cylinder walls. A windage tray is going to effect that and on some engines that may not be a good thing. Don't know for sure regarding the Cummins, but I think it's a factor there?
 

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Well, Paul, it's like this: When the crank spins at hgh rpm on an engine the back side of the journals create a negative pressure area, much like taxes due to your income. Similarly that vacuum pulls up the oil out of the crankcase, like the IRS yanks up people's savings, and the oil forms a blob that travels along with the crank. It can be as much as 1/2 the pan's capacity in some circumstances. This adds the effect of additional weight to the crank and to a limited degrees causes a resistance to rotation, but very limited.

The other name for a windage tray is 'crank scraper' because that's what it does. It fits on the top of oil pan and is cut precisely to the contours of the crank throws. They scrape the blob of oil from the crank and thereby remove the parasitic drag. Usually they are a louvered tray to encourage drainback of what little oil still follows crank.

The knife-edged crank journals are supposed to help too, but they do little and then only on real hi-revving engines. Because this oil mass is a function of vacuum behind the throws the knife edging is bordering on silliness except in allowing the crank throw to enter the oil reservoir with less reistance.
 

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This effect is another reason to go dry sump in ultra-high performance apps.
 
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