R Theory V3 Diffuser
 

RTheory just released a group buy on their new V3 Diffuser what does everyone think. Looks like it should be pretty effective paired with a underbody and front splitter.

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You planning on running the exhaust out the side like that? That's the only thing I'm worried about doing

You won't have to run a side exit exhaust like the one in the picture. The V3 will work with the majority of aftermarket exhaust systems that follow the stock exhaust routing.

Do you have a picture of one running a stock location system? If so I'll literally sign up this second.

Can you post a pic of the diffuser straight on from the back

Sorry not right now since I only bolted it up to my NA. This weekend I'll be bolting it up to an NB that has a Racing Beat Axle back. The V3 is an identical width to the V1, and the V1 fits between plenty of dual exhaust systems. The V3 will have superior exhaust clearance to the V1 since the V3 curves up around the area where the muffler sits. Versus the V1 which is a straight plane, so you either have to run a low diffuser angle or raise your exhaust if your muffler hangs low. I'll be sure to post pictures of V1's on this thread when I get the straight back pictures for Mat tonight. For the time being feel free to check out my instagram, I uploaded lots of pictures of V1's.
https://www.instagram.com/rtheorymotorsports/

I'm heading to the car right now. I'll take some pictures when I get there.

This diffuser is the first prototype. I should mention I made some minor changes to make assembly easier and much cleaner. The production version will look the same as this version for the most part. And sorry for the messy garage picture, I'll take more if needed outside when it stops raining!
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As promised, here are some pictures of some customers running V1 diffusers with a stock location exhaust system. V3 fitment will be same at the exit. Under the muffler V3 clearance will be greater than the V1.

Also I'll mention V3 requires a mild bumper cut. Thankfully The Car Passion Channel just uploaded a youtube video on how to do a rear bumper cut! :bigtu:
You can find more details regarding the V3 here-> NA/NB Miata V3 Rear Diffuser Group Buy ? R Theory Motorsports

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Can you quote some science here on the aerodynamics behind what this will do for my 2000 NB? thank'an you

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I would lower the bar even further, how about testing with flow-viz paint to show any aero benefits? Or a video driving through low area with fog? There are so many easy ways to get aero data.

Why is a curved diffuser better than one with abrupt angle changes? It appears to make sense, but I know from my 2-stroke days and building pipes, that those pipes want abrupt angle changes into the expansion chamber and not smooth or curved into the expansion chamber. I have to think that rapidly expanding air, 2-stroke pipes and aero may be quite similar?

^Flow separation.

Why don't you guys do your own research instead of trying to dog a modification you don't understand.

If you don't understand how a diffuser lowers drag and increases downforce, you're unlikely to be his target audience.

Smooth curved transitions keep the flow attached and keep drag low. An abrupt transition would likely produce more downforce, but at the expense of much more drag. The main attractiveness of a diffuser is a high L/D, so keeping it smooth makes sense.

Diffusers | Engineering basics | Aerodynamics - Racecar Engineering

Just to get this thread back on track. The above are great links for aero. Kyle Drives has many good videos explaning aero that everyone exploring aero should watch. Race care engineering just buy the book its worth it.

I understand aero and the purpose and concept of this diffuser (I have been waiting for this release and will buy one) The intent of this threat were to discus the ascetics, shortcomings and where it excels. Its pretty obvious this is functionally better than the v1 and v2. I think it looks good especially for a bolt on part. As far as downfalls what concerns me is that without a full underbody air will still follow on the topside of the diffuser and get stuck in our parachute rear bumpers. Im hoping RTheory can chime in on this part even though i know he has underbody plans in the works. The one other thing that could be a concern to me is ground clearance for loading on the trailer or a steep hill.

I would like to point out that you participant ranges on the group buy site have a gap between 15 and 20 participants. I was also curious how many deposits have already been received. I am right on the fence so if we are looking at sub $300 I will most likely jump in.

I deal a lot with incompressible fluids and venturi devices, and a diffuser appears to be nothing more than the diverging cone of a Venturi. Every Venturi has a straight slope with an abrupt change; you will never see a venturi with a curved cone. It isn't because they can't be fabricated. So while I agree a smooth transition makes sense, data doesn't always agree with what I think it should show. Or perhaps it works better, but simply isn't worth the effort?

I also know with 2-stroke pipes, the diffuser also needs to be an abrupt change. However temperature most likely is a factor here (related to compressibility).

I could purchase one and do some low-tech testing. However I have to think the market would be higher if the manufacturer did some low-tech testing as they have the product in hand. Unless of course it is simply an aesthetic device; but if that were the situation this site would suffer the same fate as clubroadster...

tag

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You guys ask great questions.
For the people asking if the V3 is designed for function or for aesthetics, we designed it with function and form in mind. We are limited to what tools we have to test the diffuser but I do have access to CFD software. With my software we can't give you values such as how much downforce is created at what speed. Although we can illustrate how fluids would flow around a certain object(s). Admittedly our software is somewhat elementary in its CFD features since we only own the entry level of this particular 3D CAD/CFD software, but it does a good job of representing how the air should flow.

I did some CFD testing on the older V2 and this is what I came up with. Take it with a grain of salt, in our software we're limited to 50 plot lines. So I had to lower the ceiling of the test area to an unrealistic height just to increase the density of the plot lines under the car. So the curve of the air from under the car will be a little milder in real life, but either way it does show that the diffuser is creating a low pressure region under the car. I'll post some similar CFD analysis of the V3 once I get some bugs sorted in my software!

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I also did a CFD analysis on the V1 and wrote a blog entry about it on the website. You can check it out here. September 19th, 2015 - Miata Rear Diffuser CFD Analysis ? R Theory Motorsports

And someone asked why run a diffuser with a curved profile instead of a flat inclined plane. Both styles work but curved profiles work much better. With a curved profile you get a more gradual change in flow and the air stays attached to the diffuser's surface much more effectively. With a flat inclined plane it's much easier for the air to stall. When I was playing around with different angles on the V1 with our CFD software the air started to stall around 11 degrees; and this was with a flat undertray under the rear subframe. Without the flat undertray it seemed to be only effective up to around 7 degrees. With the curved rear diffuser we can run more aggressive angles without the air stalling. Despite this we will still be offering the V1 since not everyone is after max downforce. This way we'll have a diffuser for different needs. :)

Fixed the gap :)

We're currently at 8 and we have a few more weeks to go. I would be surprised if we didn't hit 10 people/sub $300.

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Maybe chat with the guys over at Velox and see if they can provide any help. I know they are only doing development on NDs.

I just threw a deposit down, I'm in. How many people are in? Curious if we hit 20+ for the $275 price break.

Also in

Dude.

A venturi is a device for measuring a pressure difference, not reducing drag; 2 completely different applications of fluid mechanics. A diffuser in a pipe is not serving the same purpose; that kind of diffuser is supposed to slow flow down and increase pressure; exactly the opposite of what this diffuser is trying to accomplish. Abrupt changes in external geometry ALWAYS induce drag by creating low pressure regions at the corner. To minimize drag, you want the flow to stay laminar at the boundary layer as much as possible, hence smooth changes in geometry.

Same word, but two completely different things.


That being said, the drag vs speed curve is exponential, meaning a diffuser is only going to make a significant difference above a certain speed. For a Miata, I don't know what speed that is, but I would be surprised if it makes that much difference at the 80-90 mph top speed that a Miata on a road course is going to see.

R_Theory:

The CFD graphic is very nice, but there's nothing to compare it to. Even if your CFD can't produce accurate absolute value results, it would still be interesting to see the comparative improvement over the baseline analysis. Also, I would show comparative analyses at several wind velocities so you can get an idea of when the diffuser actually becomes useful.

What are the benefits/drawbacks between the V2 and V3?

Looks like we're at 15 (as of 8/10) people to get the next discount break at 20 units.

Ground Effect

I guess how fluid flows through a venturi has no relevance to this topic; I apologize for confusing this thread...

can this v3 be paired with the v2 sides to widen it?

You certainly bring up some valid points, thank you for that. I've been spending the last few days tweaking the design to provide better surface attachment and I'll post the final results. I'll post up some baseline vs diffuser tests either on the facebook page and/or here.

Unfortunately it cannot. V2 and V3 are entirely different.

We did hit the 20+ mark! I am beginning production on Monday, so I decided to extend the group buy deadline to Sunday. So if anyone else is on the fence, you still have time to sign up!

thanks for the response. which is going to be more effective - the wider, shorter v2, or the narrower, taller v3?

Full size pics of what I received. One side was banged up which isn't the worst thing in the world. The packaging seemed careful to guard the middle but not edges. Not worrying about that.

The construction is riveted members. The downside here is that the as designed construction, while simpler to make, has significant leakage. Imagine seeing an airplan wing with holes along the chord...

Other than the as shipped damage and construction flaw, it looks nice ;).

For anyone who can't construct their own, I'd recommend a secondary material layer or caulking the holes. It won't be as pretty but will help. In my case, we will just end up making another one in house.

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Yeah my packaging job was pretty sub-par as well. Forward mounting tabs were pretty mangled, and both of my outside "fins" were folded inward. Managed to straighten it all out enough to install though. I feel like it doesn't go out from the back of the car nearly as much as the original example pictures showed. I'm pretty not-sold on the overall effectiveness of this, even in conjunction with a flat underbelly.

Sure looks swaggy though.

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20171016_171050 by concealer404, on Flickr

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20171016_171011 by concealer404, on Flickr

Yeah, it looks great for sure...but I have doubts

I can work with it. I'll work on flat bottom things, and i'm considering making a homebrew thingy on each side to compliment it, because it's not looking good for my rear bumper cover at this point.

Once i'm happy with how it all comes together, i'll make a copy of this thing, just shove it out a good 12-16".

I'm not mad i paid for it, i'm just reasonably sure it's nothing more than drifter hotboi swag.

LOL. Just don't make your revision porous as constructed here. I'll be doing the same.

Let me know what you want a new one to look like and I can get one laser cut and formed. See my underbody thread.

Thank you both for your comments. If I remember correctly one of you emailed me regarding your shipping issue. Whether it's on a forum or through email I appreciate feedback and see it as an area to improve in. Although with one of those diffusers, the condition it arrived in is unacceptable and would have been eligible for having either damaged parts replaced or more likely a new unit shipped out had I known. Feel free to email me if you would still like to have it done.

Regarding the design, your input is noted and I'll take it upon myself to revise the design for future units. Especially to make it less porous. While I currently have my hands tied with other development, i'll make it a priority to improve on those points. Once I have significant news about the new revision I'll create a new thread in my vendor section along with any relevant data and post the link here.
About the confusion between the original pictures and actual production unit and the distance they stick out past the car, the overall footprint of the production unit is unchanged from the prototype unit.

For future reference if anyone ever has an issue with shipping, please reach out to me via email and I'll sort it out ASAP. Help me help you! My focus is to provide you folks with quality performance orientated parts. Once revisions are made, i'll see what I can do to apply those revisions to existing V3 units. Any other questions or concerns please reach out to me here or via email at rtheorymotorsports@gmail.com.

The distance sticking out thing may just be context. Example pics were on an NA with a bumper, i have an NB and i'm unsure how much bumper cover i'll be able to run on this car, for other reasons shown in the pictures. Like i said, i'm not mad i paid for it, and the shipping wasn't a big deal. I was able to straighten it out.

For future shipping feedback: The box needs to be packed much more densely. My box contained the diffuser with a single layer of the small bubble wrap around it, and 2 pieces of brown paper loosely wadded up. There were no provisions to keep the diffuser from moving around within the box, and by volume, i'd say less than 20% of the box was actually occupied.

Interested to see what revisions you come up with! :) (Can we make this bigger? Like... a good foot bigger? )

Also, any progress on the panel you were working on to go in front of this?

@R_theory

How does this fit my bumpercut?

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Looks like nothing on that car fits.

The panel gap around the trunk lid looks pretty good, actually. It's adjusted impressively well. Better than either of my cars.

Thanks again for your input!

Overall footprint of the next revision will likely be similar to the current unit, I still want it to be somewhat street friendly. Mostly i'll be revising the construction method and optimizing the curve and angle while i'm in there. Another thing is that I want to mount the diffuser differently at the rear subframe so that it sees cleaner airflow. And yes there has been progress on the rear subframe panel. I just ordered a small batch of billet parts that will accompany the rear subframe panel. Also i'm in the process of making a new panel that will likely be the final revision. I'll post up when that's mounted. Winter is coming and all the track toys have been put away for the year. But luckily I picked up a beater NB so the test fitting and real world testing can happen in the off season!

California guys be like what off season? :giggle:

It would fit both cut and uncut bumpers. If you look at the pictures of the black NA near the beginning of the thread, it has a bumper cut that looks a little higher up than yours. You would have to ditch the JDM subway handle though.

It's been a few months, can any owners report in on any track benefits and lap times?

If it's like the warhorse as far as rigidity I think they won't do to much. My warhose was far too flexy in the strakes and just the over all unit as the gauge is to thin and nothing but flat panels, not stout enough imo. I'd rather have a simple flat panel with two outside strakes like the Tesla and made thicker so it is rigid if not a thicker or formed frp unit. Aren't these too steep? I recall 7-11* being the correct rise/angle. This looks like much more than that. Most diffusers are really really flat and long. With exceptions to some really huge deep straked diffusers.

Watch the video I posted earlier. Post 14

How do you become a "former vendor" in less than a year?

By paying for it?

In any event, I was under the impression that R Theory was either going to be stopping production of things or outsourcing their designs to other folks.