I bought these rear diffuser fins from JWM, but they did not come with any drilling/mounting instructions (even though the item description claims a drilling template is provided).

http://www.jwmotorsportsllc.com/C7-C...ins_p_358.html

Any suggestions on mounting and installing these, or will my Corvette shop know how to do so? Also, these fins come in matte black. Should I get them clear coated? And since my GS came with the Carbon Flash package, I'm wondering if I should have these fins painted to match. Thanks!

 

I added a different diffuser but have 2 sets of instructions on how to get just the lower rear bumper off!

One is modified from the C7 Carbon product, which I made from my experience.
The second from a forum member with pics also for a different install set of fins than I used.

Developed my own marking method for the three screws per fin (fence) as well. You might find it useful. I did my own install.

You or your dealer may find it useful. Print the applicable pages from this PDF for your installer: http://netwelding.com/Rear_Diffuser.pdf



I have the Stage 2 aero option as well painted carbon flash. Bought the diffuser painted the same way.. Matches the rear lower bumper perfectly.

 

Who makes this diffuser?
Ah found it. C7 Carbon makes it.

 

I see your rear diffuser is one integrated piece. My diffuser only consists of four separate "blades" which attach directly to the underside of the rear bumper, to the sides of the exhaust tips. I brought my GS to a car shop yesterday, and though the owner was enthusiastic about doing the work (which will also consist of installing a front splitter, stage 3 winglets, and wheel spats), he wanted installation instructions so that he could determine the cost of labor.

 

^^^

Yep, understand but the 2 sets of instructions in my PDF show:
How to remove the lower rear bumper (also called a diffuser by GM) without removing the whole bumper. The dealer must do that for your install. I also have a video with a short section showing in done in minutes! It will take at least 30!

The second thing you'll need is locate and mark where to drill the holes. As C7 Carbon recommend and I did for mine those should be marked BEFORE the bottom section is removed. The C7 Carbon method of marking however did not work, i.e. use a clay ball (and hope it sticks) or a sharp "point" in each hole!
What I did and is in the PDF is what I would recommend for yours:
1) put wide masking tape on the GM lower bumper.
2) place the fins where you want them.
3) mark the sides with a sharp pencil
4) mark a line centered between the two side lines and that is where you will drill
5) mark the top holes by putting a piece of masking tape on the side of the fin and locate those top holes on the centerline.
6) mark that location on the center line
7) then make your own template with a piece of paper from the top hole to the other 2. Just place the paper on the bottom of the fin curved to fit the bottom and mark the center of each hole. You can even supply that now.

Took longer to write that than to do it. I also had to drill 3 holes for each fin a that is mostly what holds my assembly to the lower bumper.

 

Thank you. I am having an independent body shop do the installation of my fins. They are four pieces and each one comes with pre-drilled holes. The vendor (JW Motoring) was supposed to provide a drilling template but has not yet, though he says he will mail it (don't understand why it can't be scanned and emailed to me). So in absence of that, I can provide the installation file in PDF and tell my installer to focus on the instructions you provided above?

 

 

Thank you! I always try to pass along any helpful information I have related to cars, lessons learned, etc. Unfortunately there are too many board members that would rather more energy in telling someone to read through the FAQs, Google is your friend, etc. Sometime a person does go through those sources and still can't find the answers they seek. If you can offer someone help, please do. If not, please move along to another area of the forum.

 

I received a quote from a local auto body shop I chose to install the front splitter, winglets, wheel spats, and rear fins. I provided them JerryU's instructions. Out of that, the quote specified 1 hour labor to remove/reinstall the rear lower bumper cover assembly, 3.2 hours to remove/reinstall the rear bumper cover, 3 hours to remove/replace the front splitter (includes winglets and wheel spats), and 2 hours to remove/replace the rear fins. That's a total of 9.2 hours labor at $75/hour, and with tax it comes to $734.85. I would like to know if that seems a reasonable price, or if it's excessive. When I questioned the shop's owner about the time he quoted to remove the rear bumper cover, he said it probably wouldn't take that long, and I would only be charged the actual time it actually took. What my concern is, with so few people around here that have done these exterior modifications on the C7, I don't want to pay money for extra labor time, while someone is "exploring", or figuring out what to do, as opposed to someone who has done this before and can get right to the work in an expedient and efficient manner. About price, the shop owner said it would most likely end up in the $400 to $500 range, but the higher amount was to protect him (I guess in case it ends up taking longer than he thought). This shop has overwhelmingly good repairs for honest work, so I don't feel like the guy is going to try to take me for a ride, but at the same time, I want to make sure I'm not paying extra labor for someone to figure out the best way to take things apart and put the parts on right.

Lastly, with respect to installation of the front splitter, stage 3 winglets, and wheel spats, does it matter in which order they are installed?

 

^^^
Hmm, first if they remove the whole rear bumper, no need to just remove the lower bumper. They come off as an assembly an drilling for the fins done with them together. I just did not want to remove the whole bumper and have fit issues getting it back. Many folks have removed it to drill holes for rear spoilers or change a taillight.

If they actually charge for the time they take, that quoted to for the splitter sounds high for a pro but for a DIY, I spent that much putting on the stage 3 winglets on my stage 2 spoiler already installed when I bought the Grand Sport. (However I had to modify the stage 3 winglet install so I could use my Novistretch bra.) $75/hr is pretty good for a none standard aftermarket install- a lot less than I charge as an expert witness!

 

Thanks for the additional info, and I've passed it along to the shop owner. I just didn't want to have to bear the cost of additional labor, spent on someone figuring out how to install the parts. I would have preferred to take it to a shop whereby the people have already done this work specifically on a C7 Grand Sport, but I am in a small town and the selection of businesses is limited.