I've been researching this for awhile, trying to learn the theories and how to apply it to my build, figured I'd ask for those who have dabbled in the aero black magic.

Receiving the RE AD-GT kit soon and have been looking into rear diffusers and alike. Now I'm leaning toward a custom diy diffuser but was thinking of using the RE pro diffuser, everything I've gathered basically says you need a flat underbody to really make it work.

Has anyone attempted this? My searching doesn't bring up too much but it's very popular with Miatas it seems. I have the design and concept in my head but not sure what material would be best suited for the job.

 

The FD all said and done actually has a relatively flat body under neath, assuming you still have all of your body panels in place. People often imagine a perfectly flat as glass surface, and while this is by all means IDEAL (assuming you dont mercedes clr it, or do something like this: , aero can be scary stuff)- Its hardly the biggest issue for a *street* car.

The biggest problem with getting a rear diffuser to actually -work- for your vehicle- Is getting it low enough to the ground, and "sealing" up the sides. You need to be at heights that are relatively uncomfortable to most people for these things to really shine.

We all know the rough idea- Diffusers allow a chamber for the air under the car to expand into, which further accelerates and "sucks" air from under the car- Pulling down on the body. The biggest problem is if your cars too high, and the sides arent sealed- All your going to do is suck in an equal amount of air under your sideskirts from around the car (btw haha I dont mean literally "Sealed", just that precautions need to be made to help prevent air from getting under the side skirts from around the car), and see little to no actual change in downforce. This is why you see those low side skirts, this is why you the big flat panels that run parallel to the ground going down the sides of bodies, and this is why you see dive-planes on front bumpers (Most think they make downforce by working as spoilers on the front of the car- And this is true to a very very tiny extent. But the biggest yield to these is that they can create a nice happy vortexing pocket of air swirling down the side of your car, that serves as a barrier to prevent air above this vortex, from spilling under a car. Youll start to notice a theme with all of these pieces).

If youre going to do aerodynamic modifications to you car- Not because you like the esthetics of it, but because you want them WORK like you THINK they work-

Get yourself a magnehelic gauge. You can pick these up on ebay for next to nothing- Find one that measures no more than 1-3 inches.

This little tool will remove any and ALL guess work from what youre doing. You simply run a line to somewhere at a static atmospheric pressure (Say, your cabin), and then the other line to the place you want to check. The bigger the difference- The more youve gained.

For a good idea on how to use these, and how important they are- I can NOT recommend this guide enough, if you havent read it already:

AutoSpeed - Ultimate DIY Automotive Modification Tool-Kit, Part 3

Note this is part 3, theres a small collection of them, and theyre amazing to read.

Cheers

 

View of the stock FD underbody...



IMHO aero is mostly aesthetic. Even on track days it's not a major factor. Only when you get competitive and every second counts does aerodynamics become a factor. That said, I just installed a spoiler and ripped off my stock diffuser

Great link BTW.

 

i do love the aesthetics of it, and definitely want the performance of it. i actually have that gauge at work, for duct work (HVAC) 1 may be missing now, thanks for the link definitely going read over it all.

while im not competing at that level, probably never will, just as building the car i enjoy doing some performance based DIY. aero has always been interesting to me, a lot of the time attack cars are really experimenting with things and times are dropping while maintaining same power levels and i just want to play too! haha

 

Aero plays a BIG factor for any car driving on a decently fast course. Granted you are driving at the limit, aero shaves time off a lot in high speed zones and braking. Street Class time attack cars today are running as fast as unlimited cars from 7 years ago mainly because of aero. Without aero, you simply are not competitive anymore in Time Attacks or similar events.

One example: SLB Street Class RWD record at Buttonwillow in 2010 was a 2:01 (Pro driver Yoshihara) 2016 someone clocked a 1:48 by a private non-pro driver!