I know Mantis has played around with a functional diffuser has anyone else?
When I first built my Exotek F 104 I added a diffuser and enclosed the hole below the motor. I have just always ran the car that way and never did anything to see if it made a difference. Today I finally gave it a proper test.
I was running on a outdoor basketball court with a painted textured surface. I have been running the same layout for three days now. The track has developed a very clean line and was giving consistent laps. With this happening I decided to put the diffuser to the test with the clock.
I was actually expecting no difference with or without. Yet the times show there is a difference. It is not a big difference but a difference. In fastest lap times there was a .05-.1 second difference on a 15 second lap. I did notice a difference in the feel of the car. In tight 180 corners I had to be much smoother on the throttle or the rear tires broke loose and kick out easier without the diffuser. The car also tracked straighter down the main straight. The biggest difference I noticed is the rear tires stayed more consistent during a 5 minute race with a diffuser. Without the diffuser towards the end of a 5 minute run the tires started to drop off in performance.
Here are some pics of my setup from when I first did it. I used styrene to close off the underside of the car. After a lots of time on the car the side pieces do not fit as tightly against the chassis any more.
How everything looks now.
It would be interesting to see how a full diffuser would work on a car like the FGX where you could easily seal off the entire bottom since you do not have a rear pod suspension to worry about.