C-Max diffuser
 

Hey Guys,

First let me say a quick "Thank You" to all of you for puting up with all my newbie questions. I appreciate all the input I have received from all of you. :)

OK, warm fuzzies aside, I have begun the somewhat daunting task of building the diffuser for my C-Max.

This is a difficult task for a number of reasons;

#1 There are precious few areas to mount anything to under the rear of this car.

#2 The exhaust system needed to be lifted 2 inches to provide a proper curve and angle of the diffuser.

#3 I needed to make a subframe for the diffuser because (as I mentioned before) there are almost zero places to attach panels to under the car.

So, you can see that I moved the exhaust up 2 inches. Then I TIG welded together a 3/4 inch 14 gauge 6061 aluminum frame to which I pop riveted 4mm thick G10 panels to form the rear 14 inches of the flat section as well as the vertical fins. Then I used 4mm thick black Coroplast for the forward section of the diffuser.

What you see here is 37 inches long and 22 inches wide. The remaining areas to each side of this center section are roughly 16 inches per side. These side portions will be shaped a little different from the center and will be built as separate parts, bolted to each side of this center section.

I have 7 hours of time into this project total so far. The aluminum frame is very light as is the Coroplast. The G10 is a bit heavy, though. That (and cost reasons) is why I only used G10 for portions of the diffuser, but not the entire thing.

Oh, lastly, I will probably reduce the height of the vertical fins of the diffuser to make it look a bit better.

Being that this thing is only partially done, the results will be minimal until I have it finished. That being said, I have noticed the rear window is vastly cleaner than before. This car has had the worst rear window airflow I have ever owned. I go through a huge amount of washer fluid trying to keep the window clean and, so far, the rear window is drastically cleaner than before I installed the diffuser.

With Christmas here, odds are the remaining portion of the diffuser will take a couple weeks to finish.

Matt

Sweet!

Can't wait to hear the results.

That is a very nice job. You may be able to sell those things to other owners.

Looks nice! How well does it "furrow" snow (wink,wink)?

So far so good.

Of course, this is only about 40% of the entire diffuser. However, the last bit will be far quicker to build because I already have the foundation made. ABA testing should be really easy because this is designed to be easy to install and remove.

It is strange how clean my rear window is with this thing. I am sure it will be even better with the entire diffuser done.

Oh, my coasting is noticeably better. Also, when the engine kicks on, I cannot see any exhaust behind the car anymore. Normally my rear window is swirling with exhaust.

I will keep you guys posted.

Matt

Excellent work, I'm looking forward to those "Lotus style" diffuser endplates :D

I.m thinking of making a diffuser for my vw polo. But taking the 10 degreeds as a guideline. So if i have to cut into the under portion of the rear bumper i would not have a problem with it. I just have te think something for my hitchmount. Maybe even use it to mount the diffuser with a crossbar.

Here are pictures of the finished diffuser. The angle is 10.5 degrees. That is about as shallow as I could go with the layout of the car. That is actually pretty good, though. At first it looked like 14 degrees was the lowest angle I could achieve.

The outer air skirts are just on the inside edge of the tires. I plan on making rear wheel spats that attach to the skirts eventually.

This whole diffuser is relatively light. I have not weighed it, but for how big it is, it sure feels light in the hand.

Next is the under pan. The car has a nice nose pan and various pan inserts under the car to somewhat smooth the airflow. But, it is still far rougher than I would like.

Matt

diffuser
 

Is there a way to see the rest of the underbody?
Typically,the diffuser is disabled in the absence of a full, smooth, belly pan leading up to it.:(