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eh not really, as long as you have already removed the rear areo panel which if you have any sort of rear brace bar or anything then you have. I will say this, its ugly though, it has the tan color in most places :p might want to hit it with some black paint.

-R
 

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Discussion Starter #9
Evasive Motorsports | PH: 626.336.3400 Mon-Fri, 9am-6pm PST: Voltex

Interesting to say the least. Although I'm not sure how functional those diffusers are. Without strakes, the fins, and even one of the designs has a hump that would impede aiflow, they really seem show releated. A diffuser should help air to move out from under the car and expand behind it and combine with the fast moving air from the top.

I've been able to have a closer look at the underside of the Si and I see some real potential for a functional rear diffuser while also taking in some aesthetic enhancement also. Maybe once I get the bumper off and the stock diffuser removed I can start mocking up in cardboard. I'll take pics of the progress.
 

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Discussion Starter #10
Ok going to reveal my thoughts on the design of this thing.

-font-b-rear-b-font-lip-font-b-designed-b-font-for-toyota-GT86-of.jpg

So using this design I like the idea of extending the diffuser out a couple inches. Not sold on the wings on the side so lets ignore that. I want to bring the whole rear down a few inches with the new pieces.

SI rear 01.jpg

Here we see the Stock diffuser and upon further examination I've there is a piece further towards the front that also helps with airflow.
SI rear under diffuser.jpg The "front" rear diffuser....

Ok now I think we have a perfect start. All the mounting points are there, so mounting this thing up wont be a problem. Sweet.
What I hope to do is match up the channels with the 2 diffuser pieces and create better airflow. Also want to have bigger more prominent strakes.

Now for the gotcha.
Exhuast hole.jpg

The big ol hole on the passenger side of the exhaust. Now it really shouldn't be an issue cause I'm planning on making separate pieces for the outside rears and should be able to close that up. Now for some more time off, cardboard, and foam. Then we can start laying the ideas out.
 

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What exactly made you decide upon the rear diffuser, verses, say, a front splitter or bumper canards? Are you building this from the ground up based on preliminary aerodynamic knowledge? Or, are you merely going to make a modified, more aggressive version of our stock diffuser i.e. larger strakes, etc. (I couldn't quite determine what you're going for from your previous posts, so I apologize if it seemed obvious)?

You definitely seem serious about the functionality over aesthetics. Are you basically going to fab some cardboard (or whatever material) prototypes up essentially out of nothing? Or, if it's possible, will you be working with CAD software to develop digital models and possibly even perform some flow simulations with those prototypes before making tangible models?

Also, how, exactly, do you plan on going about testing the functionality of your designs verses each other and verses the OEM unit? Wind tunnel? Time slips? The tried and not-so-true butt-dyno?

It would be one thing if you were designing your own diffuser mostly for aesthetics, but, since you're aiming for function over form, I'm very curious to see how you go about the entire design process and how the project evolves from its current phase to the final design. I've always wanted to undertake an R&D project like this for my car, but have always felt like I don't have enough money or available resources or knowledge to truly craft something uniquely functional. Hopefully, with more time and experience in the engineering field, that'll change in the future.

Good luck in your endeavor and keep us posted!
 

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Discussion Starter #12
@Lpc Thanks. <br>I went with a rear diffuser because I saw the stocl one on the SI coupe and thought it could be made to be more functional. Looking at some of the "super cars" out there almost all have integrated diffusers of some sort. Once I realized that the coupe si has one, then I remembered we have some bottom shrouds to help with aerodynamics. It's a match made in heaven. :p Not the the Si is a super car but having those components already there, I think I could create a look that is reminiscent of a super car. As for a front splitter, I do have plans to make one along with the diffuser.
I wish I was better versed in CAD and flow sims. I love to try that first but "I is not so smart". Really once you boil it down even if it doesn't work it'll still look cool. Lol I am planning on doing a "Tuff Test" stock diffuser and one with the new piece. From some of the videos i've seen of other after market diffusers the lack of airflow along the bumper is a sign of the diffuser working.
And I'm just a moron who thinks he can understand basic aerodynamics from youtube videos. :p I will keep everyone posted here in this thread. I hope to come up with something functional but if not truly unique. Wish me luck!
 

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Discussion Starter #13
Well I finally had a chance to poke around on the rear bumper. (pun intended. LOL) While I love the idea and think it would look Bad Azz, I feel it's too much of an ambitious project. I don't have the expertise to accomplish the idea. I'm going to focus on other things with the car. Maybe some day.
 

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Where did you find the si diffuser? I'm trying to do the same thing to my 2014 EX coupe. But I can't seem to find any sites that sell the stock diffuser besides the dealer
 
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