Project #YAE92 M3: Part 5 – Basic Aerodynamics


The rear diffuser is a point of many debates. Technically you need to have a completely flat undertray to make a true rear diffuser that works properly. Most of us don’t have that but that doesn’t mean you can’t make something that isn’t benefitial. Our rear diffuser is simple, it’s more flat smooth surface for air to travel over, just like the rest of the underbody. The shallow angle provides a little bit of a diffuser effect without being so aggressive that flow becomes detached. The strakes act as guides to block tire squirt (look it up) from ruining most of the surface area and help guide the air.


Since we don’t have a completely flat undertray, air is going to get to the top of the diffuser, that’s just how it is. This could be a huge source of drag so to counteract it, we left a large area on top of the diffuser wide open to give the air a place to evacuate and not act like a parachute. This also gives the turbulant air coming off the rotating rear wheels a place to go. Without a true flat underbelly there’s more benefit to doing it this way in terms of drag reduction, which is ulimtately what we’re after.

Moving back toward the front of the car you see we have cut giant gaping holes in the front fenders. This also helps reduce drag by giving turbulent rotating air coming off the front tires a place to escape. The rotation of the wheels will pack air and build pressure under the wheel wells counteracting downforce created by the splitter so you’ve got to get it out of there.


Our front fender vents allow high pressure air a place to escape the wheel wells helping reduce lift and drag. We fabricated a smooth transition for the air to travel acrross to help expedite the process.

Last, but not least, the most recognizeable aerodynamic device in motorsports, the wing. Ours, of course made by APR Performance, is the new swan-neck version of their popular GT-250 wing. You now see swan neck wings on most every LeMans car out there so I will do my best to explain in as few words possible their benefit.

As air moves around the wing mounts of any wing, a turbulent wake is created behind it causing a flow separation. Since the underside of a wing is a low pressure area that flow separation becomes larger. A swan neck setup moves the mount off the underside of the underside of the wing completely. Since the mounts are now forward of the wing the separation created by air moving around them is no longer in a low pressure zone and creates a smaller wake and none of the flow moving under the wing becomes detached maximizing your wing’s efficiency and allowing you to produce more downforce with less surface area and/or angle. Since the top of the wing is a high pressure area, the mounting location does not have nearly the same amount of negative effect as it does on the bottom.


Our APR Performance swan neck mounted wing allows us to create more downforce with less angle than a traditionally mounted wing. Less angle means less drag. Less drag means better fuel economy and top speed. Win win.

The wing mounts for our APR Performance GT-250 wing go down into the trunk area and bolt to an intricate, super strong, lightweight structure desgined and built by 3saurus Fabrication. The bridge-mount transfers the load of the wing around our fuel cell and directly to the frame rails of the car. This, like the chassis mounted splitter, ensures that you’re using all the downforce you’re getting from the wing to push the tires into the pavement for maximum effect. Like the splitter, your wing should be strong enough to take some serious weight without anything moving other than the rear suspension of the car.

So there you have it, version 1 of our aero setup on the Yost Autosport E92 M3; the basics. A splitter to generate downforce up front, a wing to do the same in the rear and the rest of the pieces designed to reduce drag. There’s still a long list of aero improvements to do on this car but that will have to wait for a future article. Next article we’ll talk suspension, wheels, and tires!

Yost Autosport #YAE92 M3: Part 1 – We Officially Void the Warranty

Yost Autosport #YAE92 M3: Part 2 – Why Do We Have All of These Extra Bolts?

Yost Autosport #YAE92 M3: Part 3 – It's The Little Things

Yost Autosport #YAE92 M3: Part 4 – Let's Do Some Catching Up



Yost Autosport

APR Performance

3saurus Custom Fabrication

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