Yeah, I know the difference between a wing and a spoiler. I just wasn't sure whether such a small ducktail can do any good at all and whether it gets any laminar air back there. Your sample was irritating since your results didn't reflect the general opinion of "ducktails are for ricers" here. However, I'll give it a try then.

hood vents are on the list, probably Flyin Miata or Ford Focus RS replicas. Sorry, no singulär vents as I find them offensively ugly.

I'll run brake ducts too. Are yours 2.5" or 3"?

 

2.5 ducts are what the inlets for the GV lip take.

Yeah, spoilers aren't as effective as wings by any stretch but this one certainly makes a notable difference in how light the rear end feels. I may move to a serious splitter and wing eventually but I will need stronger spring rates if I do.

 

You are unlikely to get answers to this as the aero here is more aggressive than subtle. I however have been thinking along these lines for a while so will give some speculation/food for thought. The problem is your horsepower in my eyes as you could get out of shape far quicker than a lower power car.

1. An undertray and underbody will even out the aerodynamics some what but I would guess that with that much power you could have a MASSIVE wing and it would still buck pretty easily.
2. It will make you oversteer more but by how much depends on your ride height and how stable that ride height is maintained.
3. Totally unsure but logic would dictate that without the diffuser to control flow at the back more I would guess drag would be created. There is still debate over the "parachute" effect of the rear bumper but most here remove it and it feels better but it weighs a significant amount. I would guess by going flat all the way through any drag created by the bumper would simply be pushed back further.
4. Without knowing about the flow into and out of the engine bay this cannot reliably be answered but the likely answer is no given normal uses for a flap and your desire. If anything i would place a NACA duct before the cat so air is directed at it or fit some metal plate to it and attachments to your hole so it can heat exchange that way (although any efficient heat exchange design would probably wreck the underbody flow hence the NACA duct idea).

Given you power level I do not believe you can live without a wing and at least a minor splitter and underbody. With your power level i would want everything I can find, buy and build to keep me on the road.
I would guess a decent attempt at reducing drag with some mild aero would be your best bet as you would see more stability.
A 50mm splitter, flat underbody, bumper cut with curved up diffuser and high attack angle spoiler should control the air well enough for you to see something more helpful as well as stay with a realistic legal position. I would go to a friendly tester and ask what they think you could get on without breaching anything. The modifications listed would have no problem passing legal testing in the UK as long as they were strongly attached.

 

Thread ended over 10 months ago.

 

Ah thats the US EU date convention getting to me.

 

Doesn't matter, it's still relevant. Matter of fact I haven't gotten around building anything yet since I crashed the car last winter and spent most of the early season rebuilding it. So I postponed it to this coming winter.

I'll focus on reducing lift. A real splitter won't happen since I cannot legally run a big *** wing in Germany. I'll thus fab a flat floor (1.5-2.0 mm Aluminium), a wooden undertray that ends right at the GV lip and is preferably mounted at a light angle, and a big curved diffuser. That should comply with local standards

 

Don't forget a spoiler could help too. A wing isn't allowed but a spoiler is for sure.

 

I already have a KG works ducktail. Not the most effective Spoiler, but it's TÜV legal

 

It does help. I noticed a difference in high speed sweepers and very high speed braking zones. I have been reluctant to add a wing to my car so it is all I have.