CFD analysis of BRZ/FRS rear diffuser

[u/Josh]

Originally Posted by Wonderbar

The muffler shape or type makes no difference with the diffuser on. The diffuser encloses the entire cavity and covers the entire muffler.

I know. I am talking about the model without the diffusor. It matters whether you are comparing the diffusor to a stock car or a car with aftermarket mufflers.

[Wonderbar]

Ah, gotcha. I do believe it's the stock muffler design. That's a question for. @plucas

[plucas]

Originally Posted by djliquidsteele

Thats 108lbs of lift decrease. This may take some clarification from hancha, but is that a decrease from stock? If so, IIRC, thats only about 18lbs of downforce. I seem to remember that stock, there was about 90lbs of lift. I could definitely be wrong though.

Yes from stock. The car makes lift stock which is why it is described as a decrease in lift. The car makes downforce with Driveway Labs diffuser. Exact number won't be eact since the model is simplified. Cfd is a tool to improve designs, not something that gives absolute numbers. Even windtunnels won't give exact numbers ( i wrote about this in our blog).

Also a decrease in lift will give you more available grip just as making downforce.

Originally Posted by Wonderbar

Ah, gotcha. I do believe it's the stock muffler design. That's a question for. @plucas

Correct stock muffler design.

[Gunman]

It's all about the trends, not the exact numbers.

[ImAwesome]

Awesome to see this

[Anaxilus]

Thanks for this! Just a couple questions.

1-Is this w/ underpanels or w/o? Can't tell if the model is a GT86, or FRS or if the front fascia is just the model and you're running BRZ limited numbers. I assume not w/o a spoiler.

a-Would it be possible to offer sims w/ the underpanels if they are not included?

2-Is it possible to model the OE aftermarket diffusers available from Subie just for the sake of comparison? I don't think they'll be able to match what you have but it would be a nice comparisons for consumers.

3-Would it be possible to do a few sims running the Seibon and VIS CSL trunks?

4-Same for those rear roof spoilers?

I understand if all that is too time consuming or a bit OT. All of those are an order of magnitude below the diffuser in question performance wise I'd presume. Figured it couldn't hurt to ask if you find the time and resources.

Thanks again!

[u/Josh]

Originally Posted by plucas

Correct stock muffler design.

That makes your lift decrease sound very good. I would like to see the results of this same simulation, but model the car with no diffusor and a typical aftermarket muffler or muffler delete shape. This would do two things for you:

1. Validate your model. Evidence suggests the car makes more rear lift with a muffler delete. If your model shows this then you have reason to trust your model. (This is huge)

2. Show even greater performance improvements. If those numbers are compared to the stock muffler, they will be even better when compared to a muffler delete or typical non-factory muffler shape. Additionally, most people buying this are not running stock exhaust.

[Kostamojen]

Originally Posted by Anaxilus

Thanks for this! Just a couple questions.

1-Is this w/ underpanels or w/o? Can't tell if the model is a GT86, or FRS or if the front fascia is just the model and you're running BRZ limited numbers. I assume not w/o a spoiler.

a-Would it be possible to offer sims w/ the underpanels if they are not included?

2-Is it possible to model the OE aftermarket diffusers available from Subie just for the sake of comparison? I don't think they'll be able to match what you have but it would be a nice comparisons for consumers.

Same questions here. Also interested in spoiler differences and maybe even with the gurney flap.

So this diffuser works just fine with muffler deletes then?

[Zach3794]

This update just turned the diffuser from a want to a must have!

[Wonderbar]

Originally Posted by Anaxilus

Thanks for this! Just a couple questions.

1-Is this w/ underpanels or w/o? Can't tell if the model is a GT86, or FRS or if the front fascia is just the model and you're running BRZ limited numbers. I assume not w/o a spoiler.

a-Would it be possible to offer sims w/ the underpanels if they are not included?

2-Is it possible to model the OE aftermarket diffusers available from Subie just for the sake of comparison? I don't think they'll be able to match what you have but it would be a nice comparisons for consumers.

3-Would it be possible to do a few sims running the Seibon and VIS CSL trunks?

4-Same for those rear roof spoilers?

I understand if all that is too time consuming or a bit OT. All of those are an order of magnitude below the diffuser in question performance wise I'd presume. Figured it couldn't hurt to ask if you find the time and resources.

Thanks again!

Well, the answer to all that costs time and money. The diffuser analysis came out of my pocket, I do not have the ability or the need to spend the additional money on all these other things. Hancha is easy to to work with and easy to contact on here, Facebook and other means if you want to commission work from them.

My intent was to show a completely stock car and how just the addition of the diffuser can improve the dynamics of the cars capabilities.

Every project has to have a start and end point with it's left and right limits. There is so much that I want to do but it is outside the scope of my intent for the moment.

The model isn't 100% detailed, so it would be closer to what the car is like with underbody panels. The way I understand it, Panels on the bottom would actually show a decreased effectiveness of the diffuser because the air flowing across the bottom is already exiting in a cleaner manner. In theory is the bottom of the model was more detailed and the air more turbulent when it got the the diffuser; the model would show more positive effect coming from the diffuser.

[mav1178]

Originally Posted by Wonderbar

The model isn't 100% detailed, so it would be closer to what the car is like with underbody panels. The way I understand it, Panels on the bottom would actually show a decreased effectiveness of the diffuser because the air flowing across the bottom is already exiting in a cleaner manner. In theory is the bottom of the model was more detailed and the air more turbulent when it got the the diffuser; the model would show more positive effect coming from the diffuser.

In an ideal world, the front of your diffuser would link up (and bolt to) the JDM underpanels.

I currently have the underpanels and am interested in this rear diffuser for my car. May be interesting to see how the two can be blended together.

Sidenote: do you have pictures of the car on a lift, of the front part of the diffuser near the rear subframe?

-alex

[Gunman]

Ideally you'd want to bridge the gap between the JDM under panels, and the diffuser. Suspension arms may hamper that.

[PhastekSport]

Awesome! Great data.

[samuel1990]

i dont understand anything in the pictures, but i want one haha