Splitters? Diffusers?

[lunarhighway]

i slitter will work at reduceing some air going under the car but mainly at generating downforce. while reduceing under car air might cause a slight reduction in drag this air will have to go elsewhere so that's either around or over the car, and perhaps a little more air trough the radiator, but that will all take energy.

downforce will improve high speed cornering, wich is very important for setting a good lap time. it won't however mean the car used less fuel.

most racecars never run at their top speed due to all the curves so they have power to spare to overcome additional drag without loosing speed. and if this additional drag means they can go trough a corner faster than more drag might actually mean a better lap time.

a rear diffuser won't add any drag, but if the rest of the underside is relatively rough (as it is on a lot of cars) you con't see much improvement in FE

autospeed recently did a test on a honda insight with a rear undertray, wich didn't yield as much improvement as they'd hoped for.

an airdam can be a good tool to reduce under car airflow, especially if it's curved backwards to the sides.... this way you don't offer any resistance in the direction you want the air to go (around the car) and you make it easyer for some air to make it around the car rather than below it.

the best, but not always easiest thing to do is to make the bottom of the car as smooth as possible... start from the front and work your way to the back.

an undertray is a good start as it block off the rough underside of the engine

if the underside is perfecly smooth it suddenly becomes a shortcut for the air and makeing the bumper/airdam slightly higher in the center actually invites more air undermeath.

in it's finest form this can even generate a ground effect where the low pressure underneath the car actually generates downfoce... wich in turn is good if you want to go fast.


in general however raceing aerodynamics are often not a good starting point for aero mods... there's a lot written about them and a lot of aftermaket stuff available, but generally none of these things will help you much in improveing your FE.