I had ordered Shine's Spec-RE Pro diffuser a while ago and recently got around to installing it. I found that there were a lot of pictures of installed diffusers, with very little guidance on how to install. I knew the install wasn't exactly rocket surgery, but some guidance wouldn't have hurt. I hope this photo guide helps. Please add your own pointers.

I would recommend installing this with someone else. Lining it up, measuring, and cutting was a lot easier with another set of hands. Tackling this by yourself can be done, but I'd imagine it's much trickier. Thanks for the help Mark!

For an install reference for the Street Diffuser, see Crispy's thread here


Our point of reference for the install - thanks Carol and Import Tuner; "alright Mark, this is what we're aiming for":



The diffuser - Shine's Spec-RE Pro Diffuser with Center Air Diverters. It was received with several major blemishes. As they were on the inside of the diffuser, because I didn't feel like having to deal with shipping it back and waiting, and because it was going to get beat up under my car anyways, I decided to keep it. Blemishes aside, it's quite the beautiful piece!:

Hardware - Shine provided what's on the left side, I purchased what's on the right. Note - I didn't need the CrownBolt hardware:


Before:



Ready to do work:

 

I have seen installs where the factory rear lower spoiler has been fully removed or trimmed around the rear diffuser. I don't like the complete view of the gas tank, so I chose to trim the lower spoiler around the rear diffuser.

Measure the top portion of the diffuser, then measure that out from the center of the rear bumper. I used painters tape as reference points for where to cut. Note - there are several screws holding the lower spoiler in place. Cut around the screws to keep the lower spoiler in place; see below for reference. Remember throughout this install: measure twice (or thrice) and cut once! The lower spoiler may need additional trimming once the diffuser is fully installed, as the center channel is angled and not a perfect ninety-degrees. Bust out your protractor at this point if you want to get that angle right, but these cuts are hidden:



Cut around this screw to keep the lower spoiler in place:





And test fit:

 

Align the side pieces up with the rear bumper factory lines, painters tape in place:

 

My HKS Carbon Ti hangs pretty low, so trimming around the exhaust was needed to bolt the diffuser in place.



Mark had the awesome idea to use my helmet visor as a template for trimming:




We test fit the diffuser and found that additional material needed to be trimmed (yes, we measured twice, but I'd rather have to cut additional material than to have cut too much material off)


The exhaust can get pretty hot, so we added some high temp protection to the diffuser. This is absolute overkill, but that's fine:


Scuff up the diffuser with sand paper for the tape to better adhere:



Tape off the diffuser so you don't get any overspray, and paint:

 

Drill out the diffuser bolt holes. Shine provides dimples for reference. We started with a smaller bit and worked our way up for a snug fit:

 

Install the two brackets to the gas tank relatively loose as adjustments may be needed. This is where the brackets go. Note - I flipped them around as shown in the last two photos below:


We bolted the brackets last, but here is how they are bolted down for reference:

 

Align diffuser for install, painters tape in place:

Push the sides of the diffuser up, drill holes into the side pieces using the holes in the diffuser as reference:



Align the center air diverter for install. I used center reference marks to line it up perfectly: a center mark in the license plate panel, a center mark on the center channel of the diffuser, and a center mark on the center air diverter panel:






I applied 3M aero adhesive to the center diverter panel for extra assurance:


Measure, align, re-measure, re-align, and screw diffuser into the rear bumper


Bolt the front of the diffuser to the gas tank brackets - see post above.


Tighten all screws and bolts:

 

Lower:


Inspect:



Seal of approval:




Get the plate back on and enjoy!


After the maiden voyage, we found that the diffuser is too low in the front. Additional adjustments will be needed.



I hope that helped. Please let me know if you have any questions or tips for a better install.

Cheers!

 

Nice write up, I did a few things differently.

1. I used the existing holes in the rear quarter panel that is used to mount the OEM mudguards and installed riv-nuts in it. This allowed me to not have to drill additional holes into my rear fender.

2. I used riv-nuts to secure the diffuser to the riser that mount to the rear fender.

3. I used theorie's idea and made 2 brackets that mount to the licence plate bolts and extend down to the rear of the diffuser to mount it. I bent an angle at the bottom of the bracket so the bolts would be simmilarly placed where you have them.

4. I also shortened the front mounts as the diffuser is definitely too low (as you found out).

5. Used riv-nuts to mount the center air diverter.


What lens and camera did you take these photos with?

 

Thanks John. Great pointers.

For reference, here is theorie's bracket from this post. Really cool idea.







I used my wife's Canon 5D MKII with a 16-35mm lens. I got a full run down on how to actually use it this past weekend in the White Mountains, too late to save some of the pictures in this thread.

 

Lol, I thought you were using some high quality camera equipment. That setup is $$$. I really want to pick up that lens for myself one day

 

nice write up and good pics thanks OP.

 

Very nice write up, thanks for posting it

 

Do you need to trim the rear bumper in the center to fit it?

 

I'm running the same exhaust in mine and only had to trim the lip on the diffuser to clear the exhaust.

 

My wife's a wedding photographer. It's getting a lot more fun and easier as I'm getting used to the equipment. What kind of photography are you into?


Thanks Oun and Henry.


You don't need to trim the rear bumper for fitment.


Good to know. Definitely line the diffuser up and check clearance before trimming anything.

 

Awesome writeup; and very easy to follow!!!

 

Great write up ..Gonna install mine tommo.will post pics before and after.

 

So I did my install and it was fun. As you can see I did not cut my rear valance and also used my stock mud flaps.I used the same holes on the mud flaps to bolt the side pieces.
What made my job super fun was there were brackets already installed by Japanese owner for a diffuser.Feel free to send me a PM with questions.

 

Great DIY write up thanks!

 

i had no clue how to put the add ons on this helps!

 

Since you track your car, did you notice a difference with this diffuser installed?

 

Sorry for the delay

Unfortunately I didn't have a chance to do any back to back track day analysis with and without the diffuser to see if it made any significant differences. Conceptually, I think it can only help but wouldn't be 100% effective without a flat bottomed race car

I have also trimmed the lower plastic factory rear valance since doing this write up; I was thinking it was slowing down the airflow running under the car and out the rear diffuser

It doesn't look as bad as I initially thought it would without the plastic piece


Glad to see this thread is helping the community!

Feel free to PM me if you get stuck in the process

 

bump for photos? Seems the photos disappeared. Got the jist of it, just need to clarify! Thanks!