Functional aero mods
 

I'm thinking about adding a small front splitter (Devsport) which means I probably need to pair it with a smallish rear spoiler. I've already installed an underbody kit and fabricated a diffuser. My car is n/a, currently, with stock suspension. My goal is to improve aero without increasing drag.


Any suggestions on a spoiler?

Idk how functional the Devsport lip is as its not a full splitter at all. A rear spoiler isn't really needed to reduce drag, most won't. I'd consider both of them just cosmetic. The Verus ducktail has CFD data to validate any claims however, as does their splitter!

Dont get too hung up on reducing drag to the point where you are sacrificing downforce. Up to a certain point, more downforce is always good, that point isnt a small splitter and little lip on the trunk.

Are you just doing aero mods only for the sake of doing aero mods, or are you trying to achieve some sort of performance target/metric through only reducing drag? What's the end goal?

I am aiming for some drag reduction and maybe some increase in downforce. From what I have read, some mods can give you both. I realize that without wind tunnel or CFD testing there is no concrete way of knowing what combination of mods will make a change so I'm trying for an educated guess in a positive direction.

You can’t have downforce with at least a little bit of drag, but you can reduce drag while reducing LIFT.

It sounds like you should get OEM underbody panels next if your car didn’t come with them.

Functional aero mods
 

Reducing lift and increasing downforce is the same thing. You’re reducing the net lift achieved by the aerodynamic body. There’s no such thing as downforce in aero calcs. Just lift, be it positive or negative.

A car still behaves largely like a simple airfoil. Whichever side (top or bottom) has the faster air speed will have less static pressure. If the static pressure on top is smaller than the bottom you get positive lift, if not you get negative lift.

Following that, generally, drag reduction under the car decreases lift, drag reduction on the top of the car (hood,roof,trunk) increases lift. That’s why spoilers decrease lift, they increase the drag on top of the car.

Yep, sounds like a good place to start!

The oem 86 spoiler is a good option for combined performance and aesthetics.

The TRD aero stabilizer would be a good addition to pair.

Don’t expect a crazy noticeable difference, but both should help on paper.

Rear spats would be good to pair with that diffuser

Extending the diffuser under the car further/ connecting it to flat under panels ideally it would be one smooth connected transition from front splitter to rear diffuser.

Verus wheel deflectors would help

Trd fender fins add downforce similar to canards but also redirects air around the mirrors so the drag penalty is reduced.

Side skirts can reduce lift while reducing drag as well.

You said you have underpanels already? Have pics?

Attachment 204980Attachment 204980
I just got a used oem spoiler off of ebay. The underbody panels were my first aero mod. I do have panels between the floor and axles. A diffuser is ineffective without smooth air ahead of it. Getting the bottom of a car absolutely smooth is difficult and expensive but what I've got ain't too bad. I may fab up a removable diffuser extension. I didn't want it to extend too far out so I wouldn't nail my shins every time I went into the trunk. I'll look into your other suggestions. Thanks

Side splitters/skirts my be a good option for you. They prevent "mixing" and allow the underbody to work more efficiently. I'd also look at items like the little TRD fender garnishes that look like they help manage the airflow from the wheel wells.

Are you building for a class or building for funzies?

Funzies. DE 2 for now. Thanks for the suggestions.

Wish i had pics of my underside still.
But here is my list of aero. Pretty good setup for a fun daily, everything functional, and also aesthetic in my opinion.

The verus/jdm /speed factory combo underneath the car is effectively what you are after, without some custom fab work it’s about as smooth and flat underside as you can get, with the flat panels from front bumper to the rear diffuser all connected.

Aero:
Seibon FA Carbon Hood
Greddy Gracer Front Lip
Beatrush Undertray
JDM Aero Underpanels
OEM Rear Spoiler
Verus Front Wheel Deflectors
Verus Trans Tunnel Covers
Verus Rear Aero Spats
FT-86 Speedfactory Rear diff covers
FT-86 Speedfactory Rear Diffuser
TRD Front Fender Fins
TRD Trunk Stabilizer cover
TRD Aero Turbulator
STI Side Skirts

I installed the Devsport splitter. I probably should have saved my time and money. It is composite aluminum and well made but, when it is bolted to the bottom of the bumper, it angles upward by a few degrees. This is not the aero effect that I was looking for. Devsport make some wedges but this will create a gap between the splitter and bumper that will need some sort of air dam. Over the winter I'll figure some out or scrap it all together.

Yotache Foam Seal Tape 2 Rolls 1/2 Inch Wide X 3/8 Inch Thick, Self Adhesive Weather Stripping Insulation Foam Neoprene Weather Stripping, Total 13 Feet Long (2 X 6.5 Ft Each) https://www.amazon.com/dp/B07H5DHFR3...ing=UTF8&psc=1

This is what I use to fill on the bumper splitter gap. Can cut it to shape and it will squish a little to form.

Ever heard of duct tap, or gorilla tape or any of those? They work very well for this kind of thing. Even if the splitter is "touching" the bottom of the bumper, that is not a sealed surface, and no seal there greatly reduces the efficiency of the splitter.