Gurney Flap?

BGTV8

You need a proper wing to provide down-force .. the OEM stuff is simply cosmetic and marketing-driven bull-tish

Could give serious bling-factor though.

If you install a wing, then a splitter is also required because the last thing you want is the equivalent of a 100 or 150kg bag of sand in the boot/trunk which will only serve to lift the front and let more air underneath it.

Usually, first is the splitter at the front then when you have that under control, add wing - or do both as a package.

Remember also, if the splitter is generating 80-100kgs of downforce, you are going to need to have it securely mounted - my race car splitter/airdam is mounted to the chassis with 6 x 8mm bolts for precisely this reason. Where the bolts go thru the fibreglass it is reinforced with some ali plate as well - it needs to be "robust".