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  #1 (permalink)  
Old 09-29-2013, 09:27 PM
 
Join Date: Feb 2009
Location: Clinton, Michigan
Posts: 37
Default Rear Diffuser


These pictures are of my rear diffuser. First off let me say I like how the Mopar rear diffuser looks though it's not a diffuser, it's more of an air blocker, it does not help air get out from underneath the car as a true diffuser would. I'm not saying what I have made creates any kind of huge downforce (and a true diffuser would), I do think it straightens up and aids the air flow under the rear of the car. It also fills that gaping void under the back of the car that already has a pretty decent diffuser-looking shape. The car also has an SRT front fascia and Koni shocks as the the only other non-stock items.

The material it's made from is called Tegris and it's 5/8th thick. I believe it's a type of modified polyurethane. I bought the material from roushyatesparts.com, it was a NASCAR COT splitter in it's former life and was only $40 used, though what I got had not been used and was unpainted.
It looks pretty much like carbon fiber, the gray weave is part of it though it's only on the outer surfaces, it works pretty much like wood and is easily painted.
The surface texture can be seen after it's painted. I painted the fins, the panels (behind the rear axle-in front of the rear fascia) and the indented area of the rear fascia around the exhaust flat black.

Picture A: This was a mock up for position and fit, the size of the fins got a lot smaller at their final size, raw material with unpainted panels.

Picture B: Close to final size and painted, with an additional fin outboard that is at the edge of the inside of the rear tire. Left side panel shown with the fins attached, right side panel (on the left in the picture) with the fin unattached and showing the 3M double sided adhesive tape that sticks (only the fins) to the rear fascia.

Picture C: How it attaches to the under side of the OEM rear panels, long sheet-metal screws and washers. Fins at final size, one attached, and the raw material unpainted.
Attached Images
File Type: png RearView1.png (1.77 MB, 101 views)
File Type: png RearView2.png (2.17 MB, 99 views)
File Type: png PiecesA.png (2.84 MB, 93 views)
File Type: png PiecesB.png (1.89 MB, 81 views)
File Type: png PiecesC.png (2.13 MB, 69 views)
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  #2 (permalink)  
Old 09-29-2013, 09:48 PM
James1549's Avatar
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Join Date: May 2008
Location: Cincinnati ( Delhi )
Posts: 8,764
Default Re: Rear Diffuser


I don't see how your diffuser is any different than the Mopar piece. How is the Mopar Diffuser an air blocker and yours are not? Now the fin next to the exhaust pipe needs to be lengthened to match the one you added.

James


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  #3 (permalink)  
Old 09-29-2013, 10:01 PM
MoparFreak69's Avatar
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Join Date: Jan 2012
Location: Boise, ID
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Posts: 726
Default Re: Rear Diffuser


I agree, the larger fins look out of place next to the smaller original ones on the trim panel. I have serious doubts on their looks, functionality and ability to stay in place with just the adhesive. I highly doubt these will catch on....

But thats just my opinion


'05 Roadster limited with a stick
My mods so far;
225/40ZR18,275/35ZR19 Nitto INVO's
MikeR adjustable camber arms in the rear
MAF/elbow de-fin/de-baffle
ANSA muffler
Driver's seat lowering mod
Low-buck rear lowering
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  #4 (permalink)  
Old 09-29-2013, 11:00 PM
InfernoRedXfire's Avatar
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Default Re: Rear Diffuser


I could be wrong, but I always thought of the diffusers as more of an aesthetic thing rather than functional. I just don't see them as adding to the aerodynamics of the car.



Inferno Red
2004 Ltd Coupe
vin #19176 (sold)

Black 2005 SRT-6 Roadster
vin #55786


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  #5 (permalink)  
Old 09-29-2013, 11:12 PM
James1549's Avatar
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Default Re: Rear Diffuser


Quote:
Originally Posted by InfernoRedXfire View Post
I could be wrong, but I always thought of the diffusers as more of an aesthetic thing rather than functional. I just don't see them as adding to the aerodynamics of the car.
On our cars and at our level of speed, I would say they are purely aesthetic. I always thought the purpose of them was too keep the rear straight at high speed and keep the car from getting squirrely. Like multiple rudders in the straight ahead position. Maybe, maybe not.

James



Last edited by James1549; 09-29-2013 at 11:14 PM.
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Old 09-30-2013, 01:21 PM
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Join Date: Jan 2008
Location: Virginia
Age: 31
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Default Re: Rear Diffuser


I don't think they add too much performance on the xfire as that rear section is already shaped and works like a diffuser (gradual rising slope) but there are probably some benefits when getting closer to top speed. If we had a full flat panel underneath they may work a lot better. Basically they just channel the low pressure accelerated air from under the car out the back end in a way that allows it to decelerate/decompress smoothly. This should increase downforce if done correctly (from my understanding) the little vertical pieces are mostly there to prevent turbulent/slower moving air from getting in the sides and mixing in with the low pressure stuff. In this application they are not really long enough to do so (they would need to extend well under the center of the car) so they just help smooth out / direct airflow.

If I remember correctly it took them a while to get the rear end designed right to be stable at speeds. The mopar piece basically just adds strakes to what is already essentially a diffuser built into the back.


04 Black Coupe (MT)
Engine // 74mm TB // Mercedes V8 Airbox //
Handling // Koni shocks // Eibach springs // K-MAC front bushings // MikeR(RIP) Camber arms + Sway links //
Wheels // Mandrus Wilhelm (18x8.5 - 19x9.5) // Hankook Ventus V12 (235/40 285/30) //
Sound // Alpine X305 w iPod hookup in console // 4 Channel Amp Mod //
Looks // Mopar Rear Diffuser // Painted Grille // Black Console Conversion // Euro Side Markers (Smoked)
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  #7 (permalink)  
Old 09-30-2013, 02:57 PM
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Default Re: Rear Diffuser


I just want to say great work! customisation is alwyas fun! Do you have a pic straight from behind?



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  #8 (permalink)  
Old 09-30-2013, 07:42 PM
 
Join Date: Feb 2009
Location: Clinton, Michigan
Posts: 37
Default Re: Rear Diffuser


The whole point was with "rear section is already shaped and works like a diffuser (gradual rising slope)" to have more than just a "void" as the Diffuser. The tape merely holds the rear most few inches against the fascia, the rest of the big fin is very firmly secured to the panels ahead of the fascia. It's not going anywhere, and hasn't. I'm not saying it gives any great performance advantage, but it doesn't do nothing. A louver flows more air than a hole.

And yes it is more for aesthetics than function, though it does function, the longitudinal fins (in any diffuser) are there to straighten the airflow, and yes you want them as long as possible but on road cars they don't extend forward of the rear axle. These fins are as long as those on an OE diffuser on a Viper. Look at pictures of other diffusers such as http://www.roeracing.com/productcart...154_detail.jpg

The Mopar diffuser (described by them as an appearance accessory) just hangs stubs of material at the very end of the "rear section is already shaped and works like a diffuser" that are about an inch and a half wide, stick down a few inches and extend toward the front of the no further than the fascia.
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  #9 (permalink)  
Old 09-30-2013, 09:43 PM
 
Join Date: Sep 2012
Posts: 12
Default Re: Rear Diffuser


Quote:
Originally Posted by ZX2 Nick View Post
The whole point was with "rear section is already shaped and works like a diffuser (gradual rising slope)" to have more than just a "void" as the Diffuser. The tape merely holds the rear most few inches against the fascia, the rest of the big fin is very firmly secured to the panels ahead of the fascia. It's not going anywhere, and hasn't. I'm not saying it gives any great performance advantage, but it doesn't do nothing. A louver flows more air than a hole.

And yes it is more for aesthetics than function, though it does function, the longitudinal fins (in any diffuser) are there to straighten the airflow, and yes you want them as long as possible but on road cars they don't extend forward of the rear axle. These fins are as long as those on an OE diffuser on a Viper. Look at pictures of other diffusers such as http://www.roeracing.com/productcart...154_detail.jpg

The Mopar diffuser (described by them as an appearance accessory) just hangs stubs of material at the very end of the "rear section is already shaped and works like a diffuser" that are about an inch and a half wide, stick down a few inches and extend toward the front of the no further than the fascia.

There is just something about the wording of your post that makes it unbelievably hard to read.
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  #10 (permalink)  
Old 09-30-2013, 10:09 PM
 
Join Date: Feb 2009
Location: Clinton, Michigan
Posts: 37
Default Re: Rear Diffuser


Understandable. Helped me write Yoda did.
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  #11 (permalink)  
Old 10-01-2013, 03:17 AM
 
Join Date: Sep 2012
Posts: 12
Default Re: Rear Diffuser


Quote:
Originally Posted by ZX2 Nick View Post
Understandable. Helped me write Yoda did.
Haha! After closer inspection, I understand what you're saying now. Sorry about that!
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  #12 (permalink)  
Old 10-01-2013, 10:06 AM
Bill F's Avatar
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Join Date: Nov 2005
Location: Schertz, TX.
Age: 67
Posts: 1,892
Default Re: Rear Diffuser


I have mine on just for the look, however this might explain how it should work.

Diffuser (automotive) - Wikipedia, the free encyclopedia



Retired U.S. Coast Guard MCPO (E9) and ex U.S. Navy PO2 (E5) Naval Air Facility Cam Ranh Bay, Vietnam Veteran (1967-1968)


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Last edited by Bill F; 10-01-2013 at 10:13 AM.
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Old 10-01-2013, 10:06 AM
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