We may all be saying the same thing, and then again, we may all be saying something different. Either way, I don't feel the need to perpetuate an argument, because we are all basically just bench racing here, and some of us here would carry this argument into 2019. Here are some random thoughts, not in any order, and I'm not expecting (or really wanting at this point) a response.
1. A dry sump scavenge line isn't always sucking pure oil. There will be times where it will be picking up air, that's why your dry sump tanks are screened/baffled so that the air
and oil is separated. To compound that, in situations where you have a scavenge point in a lifter valley or similar, there will be times where it will be pulling a LOT of air.
Randy Gillis emailed me yesterday about this and I don't think he would mind if I shared an excerpt from his email:
"One of the cup teams I worked with at JE had a "pan camera" and logged data with varying vacuum numbers. The amount of oil "on the lens" changed dramatically with increased vacuum ( less with higher vacuum) , to the point where it wasn't too blurry at 16"s."
Cup engines have multiple scavenge points from both the crankcase, enclosed cam tunnel, lifter valley, valve covers, etc. If they have placed a lens on the oil pan where they are scavenging from, then Randy's quote backs up what some of us are saying about "pulling oil away" from critical engine parts and backs up Blair's tornado analogy. In a sense, the pump does act like a big vacuum cleaner in that respect.
2. Wearing wrist pins because of vacuum *is indeed* an issue, and is not only caused by poor parts selection or quality.
We all know who David Reher is, right? A quote from him regarding wrist pins, oiling, etc:
"Wrist pin problems were rampant in Pro Stock several years ago, and the cure was to apply some very expensive coatings. Spending $800 for coated pins is not a cost-effective solution for most sportsman racers, however; the object is to make as many runs as possible at a reasonable price. Assuming that the wrist pins have adequate strength, it’s possible to head off many problems simply by ensuring that the pins have adequate clearance and lubrication.
The crankcase in an engine with a conventional wet-sump oil pan is awash in oil. If there is a condition that’s heating up the wrist pins or stressing the piston and rod bores, the sheer volume of oil in the crankcase will carry off the excess heat. But a well-designed oil pan with a kick-out, crankshaft scraper and a vacuum pump (or a good dry-sump system) will dramatically reduce the amount of oil in the crankcase. While an efficient oil system reduces windage and increases horsepower, it can also put the wrist pins in jeopardy – another instance of unintended consequences. In fact, the wrist pins in the even-numbered cylinders are often the first to show signs of distress caused by insufficient lubrication because they are on the side of the engine that has much of its lubrication stripped away by the crankshaft scraper and oil pan kickout.
In this situation, my recommendation is to increase the wrist pin clearance. Most engine manuals recommend wrist pin clearances between .0008 and .0010-inch for conventional engines; my advice is to run .0020 to .0022-inch wrist pin clearance in a serious drag racing engine. My perspective on engine clearances is straightforward: When in doubt, a little loose will seldom result in catastrophic failure, but a little too tight will almost always cause problems."
3. Maybe I'll pull the oil pan off of the engine I posted and glue in a plexi window. Just kidding.
