What Is Crankcase Windage?

When a piston is going down in an engine, it pushes air into the crankcase. When another piston is going up, it draws air out of the crankcase. Pumping air back and forth can cost horsepower. Cycle World Technical Editor Kevin Cameron explains how manufacturers reduce such losses.
One of the proud claims made by the Japanese motorcycle industry is that much of the horsepower gain achieved since the 1980s has come from the reduction of friction. That’s a good thing because any power recovered from friction can be used for intentional purposes, such as rapid acceleration. As Mr. Honda once put it, “Primarily, essentials of the motorcycle consist in the speed and thrill.” He said that in 1959 in the manual for the Benly 125 twin.
I have before me a CBR600RR crankshaft. This is a flat crankshaft because it has two up and two down; the crankpins are at 180 degrees from each other. That means in each of these “twins” the pistons are alternating. When one piston is going down, it pushes air into the crankcase. When another piston is going up, it draws air out of the crankcase.
If you look at the upper half of the crankcase, you see the four cylinders, which are normally blocked with pistons going up and down in them. When those pistons go up and down, the air that they push down into the crankcase has to go from one cylinder to the other and then back again every 180 degrees. If there is resistance-if it is hard for the air to get from one side to the other-that will resist the motion of the pistons. In fact, it is very easy to lose several horsepower at high rpm pumping air back and forth inside the crankcase.
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[@charlestackett7137]

My instructor did not explain this very well, or I missed it. So I'd like to thank you for supplementing what I'm learning in class. For whatever reason, I understood your explanation better.

[@888jackflash]

Love this guy. I'm so glad they have him on these videos; I READ his (great) stuff for many years.. this is better

[@trumanhw]

Running vacuum in the crank seems both genius and obvious after you say it ... such that I wonder why cars wouldn't run at least in partial vacuum..? (LOVE your series. You explain things SUPERIOR ... BY FAR!!! To Engineering Explained ... I LOVE your style of teaching (and knew it as soon as you began speaking). YOU don't just say "what" something does, you say WHY it does it. It's both frustrating and confusing that other channels omit this principle. Imagine saying "some people ran the partial vacuum in the crank" without mentioning that it creates oscillating pressure spikes between them in the first place.

[@MechaniclifeJDM]

BMW runs vacuum in the crankcase

[@trumanhw]

@@MechaniclifeJDM Very cool. :) In returning to look at this video, it pains me a little to see how few watch Kevin Cameron's series. I'm almost afraid to hate to ask why no more videos were made in the past 4 years. I googled Kevin Cameron but found no updates in the intervening period. Hope he's ok.

[@MechaniclifeJDM]

@@trumanhw Thanks. We all only get so many breaths brother, go enjoy a few today. Engines only get so many revolutions of that crank. Volvo D13’s actually count lifetime engine revolutions 😜

[@DearMajesty]

These videos are incredibly cool. Love Kevin

[@robertwolfiii8711]

Thanks for the instructional university class

[@micyclesport]

Learned something new!

[@upsidedowndog1256]

A windage tray in my Ford 289 freed up about another 1000 usable rpm.

[@trumanhw]

Awesome. (and exactly what i asked before reading comments; _why don't cars do this?_ ) ... ps, cool name choice; I'm sure hippie chicks dig it. :)

[@upsidedowndog1256]

@@trumanhw The hippie chicks dig it until it screams past 6000rpm, I shift it at 8000 with the left front tire off the ground. They don't dig that very much. Most that I know are old chicks now. Mustang sounds better than NASCAR engines at 8000 and it pulls hard from 6 to 8000.

[@tigercs1]

This isn't on the Ask Kevin Cameron playlist :(

[@daveyt4802]

Nice.

[@SirChevy]

I thought windage was power lost due to oil wrapping around the crankshaft. I didn't realize that air was the most significant factor.

[@AnonyMous-to2vi]

First

[@grabir01]

Another reason Electrics are the future.

[@MechaniclifeJDM]

We know, we know man… Elon Musk is awaiting his rectal sniffer, run along now…

[@billshiff2060]

Nope.