Underbody airflow

[Ohmess]

Looking at the variety of air dams on the e9s in Monterey stimulated a discussion about underbody air flows and about whether the splash tray has an important effect on air flow under the car at higher speed. At a minimum, it would seem adding a splash tray to a car without one would be an improvement, but how much of an improvement and at what speed?

There was also some debate about whether an extension of the splash tray to cover at least part of the drive shaft tunnel might be beneficial. Obviously, if this is not done correctly, it could add both weight and drag.

Has anyone previously looked into this?

 

[79aggie]

I don't think the base coupe is very aerodynamically efficient. The bubble canopy and erect windshield are no help.

The Group 4 and 5 body "enhancements" surely improved it, but I haven't seen any underbody aero work on any other than the ducts for cooling the front brakes. The engine compartment needs to eliminate heat off the radiator and with a front air damn you get a fairly large low pressure zone in the engine compartment, which is good for drawing air in from the front grill and creating down force. Putting a splash tray under, or extending the underside of the air damn may help increasing down force at the front wheels but I think sealing off the tunnel would probably not help much, and probably restrict air flow under the car and dissipating engine compartment heat, but yea, the flatter the underside the better. I always felt that the coupe was a bit light at the back.

Lotus (or Chapman anyway) designed the mid engine Europa as a pretty flat slab from the front nose to the engine compartment which created a large low pressure area enhanced by the cabins back window, the idea was to create down force at the rear wheels and draw a bit of air from under and up through the engine compartment to help dissipate heat. The Europa had one of the lowest coefficient of drag for a production car for a long time, of course it helps that its a tiny car. At high speeds it does tend to speed boat onto a air pressure wave and Lotus added the chin spoiler to mitigate this but to be honest it needs a bigger one cause at 95 the front wheels kind of stop beign as telepathic as the car seams to be at lower speeds and lateral wind loads are a bit disconcerting, specially with a semi's wheel center at eye level.

 

[HB Chris]

The splash pan does a good job of protecting a recently powder coated subframe but that is about it I think. Even the 240 Volvos had them.