Undertray / Flat Floor

[TBK]

Disclaimer: i'm not very knowledgeable about this, and i'm just trying to learn and experiment.

I'm sure people have experimented here, but i can't seem to find anything i can learn from.

I can't fuly seal off the area, as i'm limited by class rules, but i can still get very close.

My front splitter does front splitter things and extends to the aluminum undertray, and the rear diffuser reaches the diff basically.

So imo that leaves the following areas of improvement:

1) the exhaust area, and solving for the heat management issue somehow
2) better routing under the diffuser vs letting some air escape above it
3) routing air from the sides back out. e.g some strake that direct air outwards at point B in the diagram below. And maybe something similar in front of the rear tires.

Aluminum or a composite would probably be the material i experiment with. Really just looking for incremental improvement here, nothing magical.

Anybody done anything interesting here that they can share?

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[PowerGetter]

if you're tuning aero to meet class spec, I'm assuming you're referring to the fact that you can't have a full flat floor. Besides how the car comes from the factory and the rear diffuser must start/end at the rear center axle line -- the rear diff area as you mentioned.

With that acknowledged, there's actually not a lot to improve on when looking at the limitations of the class you're spec'ing. The factory "floor" is actually pretty good on the Supra. CFD shows that the front wheel wells are HUGE drag inducers so look into "fender" vents on the hood and an aftermarket fender that has a cutout like the EVS fenders. Rear diffusers can still help on the A90 without a flat floor (obviously not optimal but can still help) as long as it's at an optimal height; as close as possible to starting height of the diff. Also, a vertical "lip" would also help keep the air below and attached to the bottom side of the diffuser.

I was previously using the Verus rear diffuser but have moved on to something more substantial for the track.

 

[Gabe]

I was previously using the Verus rear diffuser but have moved on to something more substantial for the track.

Which product?
Pictures and perceived benefit?

 

[TBK]

if you're tuning aero to meet class spec, I'm assuming you're referring to the fact that you can't have a full flat floor. Besides how the car comes from the factory and the rear diffuser must start/end at the rear center axle line -- the rear diff area as you mentioned.

With that acknowledged, there's actually not a lot to improve on when looking at the limitations of the class you're spec'ing. The factory "floor" is actually pretty good on the Supra. CFD shows that the front wheel wells are HUGE drag inducers so look into "fender" vents on the hood and an aftermarket fender that has a cutout like the EVS fenders. Rear diffusers can still help on the A90 without a flat floor (obviously not optimal but can still help) as long as it's at an optimal height; as close as possible to starting height of the diff. Also, a vertical "lip" would also help keep the air below and attached to the bottom side of the diffuser.

I was previously using the Verus rear diffuser but have moved on to something more substantial for the track.

I do both vents and the fender slit as well. I'm actually in the process of swapping out the fenders now into the EVS ones. Pic of my current setup below

The diffuser lip thing is something i did consider to keep air from going above it. Currently running the Verus diffuser and i'm not sure about the best way to go about that. Probably an aluminum sheet folded around the diffuser angled upwards. Would have to be 2 separate pieces as well because of the cutouts.

 

[itzTang]

I do both vents and the fender slit as well. I'm actually in the process of swapping out the fenders now into the EVS ones. Pic of my current setup below

The diffuser lip thing is something i did consider to keep air from going above it. Currently running the Verus diffuser and i'm not sure about the best way to go about that. Probably an aluminum sheet folded around the diffuser angled upwards. Would have to be 2 separate pieces as well because of the cutouts.

Is the front end different shade?

 

[PowerGetter]

Which product?
Pictures and perceived benefit?

clean and accelerated air out of the rear. The faster air can travel from the front of the car and out the rear, the more downforce can be achieved. A dirty floor and a dirty rear "clogs" up the velocity of air passing through the bottom of the car, which decelerates what's happening at the front of the splitter.

Faster air out the back = faster air through the splitter = more downforce. There's a lot of variables that go into how effective the diffuser is however, they're almost always a net benefit as long as certain criteria is met.

With all that said though, a rear diffuser is probably not worth any of your money until other parts of the car are sorted.

Edit: you asked for pictures

This is the RSFuture rear diffuser I'll be running. The mounting solution is currently being fabricated.

I was initially going to go with a custom sized rear diffuser from Zebulon but ultimately decided to go with RSFuture. Below are scans we were working on with Zebulon to work with stock exhaust mounting and to meet class spec with the diffuser starting at the rear center axle line

 

[TBK]

Is the front end different shade?

The fender is lol, since it was a painted CF piece. Looks worse in direct sunlight like you see there. Its being replaced now with an EVS fender, so hopefully the color matching turns out better this time

 

[i3igpete]

With all that said though, a rear diffuser is probably not worth any of your money until other parts of the car are sorted.

Eric at verus says a car with a dirty underbody will see a larger benefit from a rear diffuser than a flat floor car, and has seen this trend across multiple different vehicles

Jump to 10:28

 

[PowerGetter]

that's not wrong. The rear diffuser would end up working harder on a car with no floor attached. However in totality, a car with a flat floor attached to a rear diffuser would provide more downforce as a whole because air is allowed to travel smoother and more freely at a higher velocity from the splitter. Where on a car with a dirty floor would have a decreased velocity at the mid section, clogging up air at the front splitter but speeding up again at the rear diffuser.

 

[i3igpete]

Yep, he says that about 10 seconds after the timestamp i mentioned

 

[Gabe]

This is the RSFuture rear diffuser I'll be running. The mounting solution is currently being fabricated.

Thanks for showing. I am currently running the Verus’ max downforce package and it works fine although I can’t really pinpoint to any particular component, including things that are outside of all the surfaces like suspension tires, the fender vents etc.
out of curiosity will look at that product. I like that the Verus stuff has materials that are better suited for extreme impact. I have had bad experiences with CF and Composite materials on car applications because they are strong but brittle.

 

[PowerGetter]

RSFuture often times works with local clients and don't ship out. But your mileage may vary if you speak to them (if you're at all interested). But I agree, it's significantly more convenient to have off the shelf stuff as it's usually easier to replace. All the custom stuff is great until you need something repaired/and or replaced. Also if you're currently happy with your current setup then I'd suggest not even looking at the custom stuff until you're ready to go full race car vs street/track car.

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