The smoother and faster the air flow under the car the better the downforce. Le Mans sports car have the entire underside completely flat and smooth with an extractor at the rear to continue the smooth air flow. I read somewhere that the resulting increase in downforce is comparable to spoilers/wings on the topside. I don't know about that statement but a flat underside is certainly crucial to maximum downforce at high speeds. (Bernoulli principle in physics)

I took mine off soon after I bought the car so that oil changing would be easier. I put it back on at my first track day thinking that it would produce some degree of improvement in downforce. I also thought about making additional smooth plates to smooth the air flow under the entire length of the center of the car. In the end I worried about trapped heat along the exhaust causing more problems.

There certainly are engineer/physcists on this board that know a great deal more than I about airflow.

 

That plastic panel has no purpose. Car manufactures put extra parts on cars just to provide assemblers and servicers unnecessary work and increase costs they pass on to consumers like us.

 

David your wrong, Jason is correct. The splash guard doesnt go that far back. You will be fine not running one guys.....

 

You should see the underside of a Lotus Elise--completely flat. That thing is beautiful.

 

'Lotus Elise'---and Jack slips off into dreamlike reverie...