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Old 08-29-2010, 02:23 PM   #1
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Default rear diffusers

who is running a rear diffuser. i would like to discuss design and see some pics.

i want to make one out of fiberglass to fit my car, with the wizdom bumper i bought. i have been reading online. what i see is that the magic number is 7 degrees of incline off your refference point (flatbottom of the car) . i want to make this thing go from the diff up to the bumper, i havent measured but off the top of my head its like 2ft in distance, at 7 degrees that would only give me about 3.75" of rise. that seems like a very little amount when looking at diffusers on other cars.


any thoughts?? would a dual plane diffuser work, like one on top of another
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Old 08-29-2010, 03:02 PM   #2
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Not that it would help,But...I remember that 7* is a very specific angle when It comes to Fluid dynamics,Though I dont remember why.I believe that It is the maximum ratio of distance to rate of expansionthat will not cause turbulance.
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Old 08-29-2010, 03:26 PM   #3
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i think your right rev. if i remember correctly, the range is 3*- 7* of range. mine is just over 5deg. if it's too steep the air separates from the diffuser making it much less, if at all, effective. if you want it to blend into the bumper, and it's up higher than you need the diffuser to be, you just make a smooth bend at the very end of the diffuser to meet up to the bumper. i actually cut out my bumper above the diffuser to release any trapped air. i've seen alot of other "pro" race cars like that also, so it must not affect the diffuser.
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Old 08-29-2010, 03:41 PM   #4
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Name:  90_miatawizdomrear.jpg
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i know its a crude drawing, but thats my bumper, im thinking the uper level can be a vent for exhaust and diff heat. the lower will be the actual diffuser
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Old 08-29-2010, 03:54 PM   #5
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https://www.miataturbo.net/showthrea...light=diffuser

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Why do you need a diffuser for drifting?

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Old 08-29-2010, 03:56 PM   #6
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When you make one make two so I could put one on my bumper
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Old 08-29-2010, 09:31 PM   #7
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https://www.miataturbo.net/showthrea...light=diffuser



Why do you need a diffuser for drifting?

cause id like to do more than just drifting, im quite a big fan of time attack and roadracing. i watch F1 religiously
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Old 08-30-2010, 02:09 AM   #8
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Pic stolen from another thread in the raceprep section. I don't know anything about the car and not very much about rear diffusers but figured this would help.

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Old 08-30-2010, 02:12 AM   #9
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cause id like to do more than just drifting, im quite a big fan of time attack and roadracing. i watch F1 religiously
Word.

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I just got major wood.
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Old 08-30-2010, 05:53 AM   #10
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see that looks bad *** and all, but im wondering if the incline is to agressive? and it curves up and then flatens out at the end, i see that being like a speed bump
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Old 09-01-2010, 01:13 PM   #11
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see that's what I was talking about. the curve up is at the very end. the important part is from the lowest point you can see back to the diff area. that's the part getting measured. at the steep curve up the airflow has all but detached at that point. only problem I see is that the fins are very shallow at the important part at the very bottom. again, I'm not an aerodynamicist if that is a word, I'm just going off of what I have read about it. I don't know how much downforce my diffuser is making, but I can tell you one thing for certain, with it, my car is much more directionally stable. I don't have to make any steering corrections at highway speeds and above. regardless of head/crosswinds of 40-60mph gusts, the car will track absolutely straight. cool thing is sometimes in a big gust, the car will feel like it hits a wall of air, and I can actually feel the car get pushed down (I have a big splitter and wing also) but it will not move a single inch in any direction. I live on the gulf coast so I have driven in windy conditions a million times. not to mention I always drive to the track so ive put alot of miles on with full Aero.
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Old 09-01-2010, 06:29 PM   #12
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Originally Posted by thesnowboarder View Post
Pic stolen from another thread in the raceprep section. I don't know anything about the car and not very much about rear diffusers but figured this would help.

the major issue i see with this one is that the oem bumper is still a big wind catcher where as the red car a few posts up is much better flowing.
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Old 09-01-2010, 09:49 PM   #13
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Originally Posted by spoolin2bars View Post
see that's what I was talking about. the curve up is at the very end. the important part is from the lowest point you can see back to the diff area. that's the part getting measured. at the steep curve up the airflow has all but detached at that point. only problem I see is that the fins are very shallow at the important part at the very bottom. again, I'm not an aerodynamicist if that is a word, I'm just going off of what I have read about it. I don't know how much downforce my diffuser is making, but I can tell you one thing for certain, with it, my car is much more directionally stable. I don't have to make any steering corrections at highway speeds and above. regardless of head/crosswinds of 40-60mph gusts, the car will track absolutely straight. cool thing is sometimes in a big gust, the car will feel like it hits a wall of air, and I can actually feel the car get pushed down (I have a big splitter and wing also) but it will not move a single inch in any direction. I live on the gulf coast so I have driven in windy conditions a million times. not to mention I always drive to the track so ive put alot of miles on with full Aero.

Spoolin, happen to have any pictures of yours?
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Old 09-01-2010, 10:12 PM   #14
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so for materials im gonna make mine from black fiberglass. from fiberglast.com
using ther 2000/2060 epoxy resin. im gonna vacuum bag it as well. ill have to 1st make the plug, then the mold. this prob wont be for a little while but i will keep you guys posted. im gonna take a stab at a smaller composite project 1st, custom canards for my autokonexion bumper. badass like voltex style ones
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Old 09-01-2010, 11:55 PM   #15
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Spoolin, happen to have any pictures of yours?
I have some. not sure if I have any since I made a cutout in my rear bumper. I'll post a few, looks like Sam's though except on a stock bumper.
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Old 09-02-2010, 08:29 PM   #16
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here's one, it's hard to see though

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Old 09-03-2010, 11:58 AM   #17
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I plan to run one in my track only car... Taking one from another car and modifying it to fit without altering the center-section of the diffuser itself. Should work nicely coupled with a flat bottom and front splitter I have in the works as well...
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Old 09-03-2010, 12:37 PM   #18
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Old 09-03-2010, 12:42 PM   #19
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I would imagine that the only way to make the diffuser really effective is if there is a sealed off volume under the car.
So... side skirts? Front wheels sealed off between splitter and skirts?
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Old 09-03-2010, 01:43 PM   #20
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Quote:
Originally Posted by Full_Tilt_Boogie View Post
I would imagine that the only way to make the diffuser really effective is if there is a sealed off volume under the car.
So... side skirts? Front wheels sealed off between splitter and skirts?
This is pretty much the truth... Just adding a rear diffuser won't really gain you anything except weight off the ***-end of the car without a fully functional aero package. But you will be JDM as fvck though...
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