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Windage Tray for Stroked Engines - What's Your Problem?

Blowin' In The Windage
Andrew Koppenhaver, via CarCraft.com: I'm a longtime reader and was happy to see the 347 stroker in the Mar. '10 issue. I'm not much of a Ford guy, but I am in the process of building a mild mill for my '78 F-100 and have been considering one of these stroker kits for some easy displacement. It was good to see an article that addressed some of my concerns and questions that have been stacking up in my head.

I'm writing this because of your final comment about using an aftermarket pan or windage tray. The article says in a comment by JMS, "The extra stroke tends to dip the counterweights into the oil, causing foaming and loss of horsepower." It's my understanding that when you grind more stroke into a crankshaft, it comes out of the rod journals, not the main journals, so that your crankshaft centerline stays the same. This being true, how can extra stroke cause the counterweights to dip into the oil? I could see the rod ends dipping in because of extra stroke, but not the counterweights. Can you shed some light on this? Also, isn't windage really the mist of oil present in the crankcase?

Jeff Smith: The comment could be termed an colloquialism, Andrew. Here's what's happening. Stroke is defined as the distance of the connecting rod journal centerline from the main journal centerline. The original Ford 5.0L engine used a 4.00-inch bore and a 3.00-inch stroke. To calculate displacement, use the formula bore x bore x stroke x 0.7854 x the number of cylinders (4 x 4 x 3 x 0.7854 x 8 = 301.6 ci). The 347ci engine bumps the stroke from 3.00 to 3.40 inches. This 0.400-inch stroke increase means the rod journals now extend another 0.200 inch farther away from the crankshaft main journal centerline, which puts the end of the rods that much closer to the bottom of the oil pan. This additional stroke really doesn't dip into the oil in the sump, but it does swing a wider arc, which means the ends of the rods will now be traveling at a greater velocity than a 3.00-inch stroke for the same engine rpm because the rods are traveling a greater distance.

You are correct that the term windage references the oil mist present in any engine. It's a combination of oil returning back to the oil pan and oil whipped by the spinning crankshaft counterweights. Oil level, sump depth, outside g-forces on the oil, windage trays, oil viscosity, oil temperature, bearing clearances, and probably a dozen other factors all play into this scene. The crank doesn't really dip into the oil level in the engine, but the counterweights are most certainly affected by having to travel through this oil mist. That's why most good performance crankshafts are tapered or knife-edged as opposed to having a blunt leading edge moving through the oil mist inside the crankcase. With a more aerodynamic shape, the crankshaft counterweight will expend less horsepower to travel through the oil mist at high engine speeds. At normal engine speeds-say less than 4,000 rpm-windage probably isn't a real issue. But with a longer stroke and engine speeds above 6,000 rpm, this becomes a significant point worth addressing.

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