This is true. I have yet to make this type of setup for an RX-7 so it's hard for me to prove firsthand, though I have worked with one on a Mk-II MR2. If you've driven a stock MR2 at highway speeds, you know that the front end gets pretty loose. At speeds over 100mph a lane change is downright unnerving.

So, my friend and I built a front splitter, and eventually a rear diffuser with some panels to smooth out the bottom of the engine bay. The MR2 has the benefit of being almost perfectly smooth from the rear-1/3rd of the car forward, so smoothing out the underside wasn't much trouble. We started with just the front spoiler, which helped a little bit from 70-90, and a lot from 90+. Later on we added the diffuser and lowered the car as well. After some tweaking of the rear spoiler and front splitter, the difference was impressive. From 70+ the front end was rock solid.

Now, at very low speeds I won't argue that it's not going to be of much use. For instance, these mods would be useless on an autocross, especially just a front splitter without a diffuser/rear spoiler/underbody panels. But on a road course or highway driving I think the difference is enough to make it worthwhile.

 

Yes, that is the purpose. The higher speed of the air creates lower pressure, making a suction.

Sideskirts aren't necessary to create the low pressure.

 

lol, is that a door sweep?

 

FYI...

Splitter Theory

This next one is from a very good website on prototype racing/design.

Diffuser

 

I've read that a rear soiler does nothing until you get around 100 MPH. Most look good, but have no purpose.

 

The angle of attack is also important. Most ricers are simply adding drag without any appreciable down force.

 

Ah, the magical 100mph theory that takes nothing about the spoiler's or car's shape and aerodynamic characteristics into consideration, but somehow is always right.

 

 

From experience, there doesn't seem to be any adverse aero affects on my 80 GS until I get over ~95 mph.

Above that speed, the front does get light and there is marginal lifting but nothing scary until you get over ~115 mph, then you actually can notice a difference in handling. This is with new shocks, strut inserts, springs, and bushings, so its not any loose suspension bits causing the light feel. I've experienced aero afftects in other cars at these speeds and the RX7 is fairly tame but a front spoiler or dam will improve things at speed but may lose you a mpg or at lower speeds.

Its true that most cars can't benefit from the aero bits until you get ~100 mph give o take 10%. Unless your doing Solo 1 or track events you will very rarely be able to get to these speeds in most parts of the US. Although, texas did raise the limit to 80 and theres Wyoming and other western states where maybe this isn't true. Here in the east coast its very hard to get a clear highway thats smooth enough to do this on.

My 2 cents.

 

Just so you know the foils on your rear defuser should be straight. The idea is that they will smoth out the air under the car and increase it's speed so when it hits the turbulant air off of the rear of the car it will speed up even more therefore increasing downforce. Pick up this months and last months Sport compact car. they both have general ideas on areodynamics and give some great pointers and basic knowlege.