2005 & 2006 Ford GT Rear Diffuser

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The Ford GT is an awesome car. It truly is a marvel how it can be at home on the track and on the street.

Unfortunately the street can be a harsh environment for a performance car. Especially one that sits so low. GT owners have found that getting in and out of parking lots and up and down some hills (Seattle especially) can cause the rear diffuser to scrape and drag on the ground causing damage.

STILLEN has been involved from the beginning of this car in the form of racing and performance upgrades. STILLEN has designed a couple of different diffusers that will handle the abuse that the street can dish out. They have made a diffuser that is made from a durable urethane and provides optimum downforce as well. They have also made one that is the same size as the original as well. It is easy to install too. You can read about it on their website here.

Here are a couple of pictures to show how it is installed.

First we rack up the car and take off the rear lower pan and drill out the rivets holding on the original diffuser.

Here are the diffusers from STILLEN. They have small indents for markings on where to drill the holes and it also is formed with a slight indent so it slides into place perfectly.

Then we rivet the new pieces on and re-install the rear lower pan.

Essential Mods

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The first thing we did to my Mustang GT was upgrade the exhaust system. We swapped out the stock system and put on Ford Racing Touring Exhaust (check out the “Exhausted” post) and GT350 rear valance. I ordered it before I even took delivery of the car. I love it. It barks but isn’t annoying while cruising. I use this car as a daily driver so it is important to me not to be too loud or drone. I had planned on getting the Track Key as well, but Ford Racing has pushed that back until the 4th quarter of this year.

So, the next thing to do was install a set of Steeda springs which were courtesy of Mr. Hood, a gentleman that had us do some impressive upgrades to his 50th Anniversary Mustang GT (see the post on this awesome car). Steeda makes many different packages and this is the Progressive Sport spring. It lowers the car an inch in the back and an inch and a half in the front.
I also needed to install some way to pull the vehicle out of the sand traps or grass if I go off track at one of the local tracks. Ford didn’t make a provision for this on the 2015/2016 Mustang (including the GT350 series car) which is odd since people do run these on the track. And while many of the Tow companies that come to the races are concerned about your ride, it is very tough to pull one of these out since most of them are lowered. I am working on one for the rear of the car, but purchased one form Dusold for the front. I am also making a front license plate bracket that will bolt to it.
I did some cosmetic things as well while I was “in there”. I took off the Intake Resonator Sound Tube that Ford runs from the air cleaner box to the the Firewall port. This is supposed to accentuate the engine sound. That is now missing. I will cover taking this off, as well. It was not designed to come off once the engine is in. Just say’n! I also took of the Coil over Plug covers and installed some cool ones from Ford Racing. Very simple and looks great.

I started at the front with Roland’s (“Buff”) help. I pulled the struts and used the wall mounted spring compressor to take off the original and install the Steeda springs. The first thing that really stands out besides sitting lower, is the car no longer dips or dives on the initial braking. It is really firm without being too stiff. It now goes around a corner like it is on rails. Having watched Buff do a couple of these already (I did read the instructions beforehand) it was a easy job. After doing the front it was off to the rear. This was a little more work as we had to lower the rear sub frame a bit. Not bad though. When we were all done, it was off to the Hunter Alignment machine. You will have to align it for sure. Lowering it does indeed change the alignment. If you do this at home, make sure to get it aligned ASAP!

Here are some shots of the different components as we did the job.

Front springs
Rear springs
The blue ones are much stouter.

Ride height before and after
  Stock Lowered
Front 28 3/8” 27 1/4"
Rear 28 1/2” 27 5/8”

Next, I pulled off the COP (coil over plug) covers and installed the new Ford Racing ones. After disconnecting the PCV tube, they just pull straight up and out.
COPS by Ford Racing

I also took the time to take the Intake Resonator Sound Tube off. I am not a “hater” of this device (as some say when you take this off), I just don’t think it is necessary. I honestly can’t tell the difference now that it is off. I think the exhaust is loud enough that it doesn’t provide any extra sound and I don’t need an extra device taking up space under the hood. You can see from some of the following photos it was a bit of a bugger to get the retaining nut off that bolts it to the firewall. I also needed to plug that hole once it was removed. When we put Whipple Super Chargers on they provide a plug (Ford part # ) since this part gets removed. I will mention, be careful not to knock off the rubber drain (water drain for cowl) difusser that is just above it. I sucks trying to get it back on.

Way down there somewhere!
I think the nut is down there somewhere! When the intake manifold is off (like when doing Whipple Superchargers) this is easier to get to.
Tool too!
You sometimes have to get creative with the tools.
It is extracted!

For the tow hook conundrum, for the front, I purchased a complete system from Dusold and I will say, it was an easy install and fit perfect. A couple of notes on this. If the car has adaptive cruise control, you will have to modify the bracket so that it clears the tow bar. If you have a GT350/GT350 R, you will have to modify the metal brackets that these models have a well. I am fortunate to be able to try this on multiple cars since I work at a Ford dealership. Also, the bolts (provided in kit) are smaller than the original bumper to frame horn because of the brackets. On the drivers side, have some patience. There isn’t a lot of room. Not bad though. Here are some pictures during the install.
Removing the front shield
Here I got some assistance from one of my technicians! Lots of push pins and bolts holding this on.

Bumper mount
This is the drivers side. You remove the stock nuts and the tow bar mount slides right on and then you use the nuts provided to tighten down. This is where you would have to modify the adaptive cruise radar mount if equipped. Keep in mind, if you do have adaptive cruise and you move the bracket, there is a very specific adjustment for it.
Here is the bar before install.
Bumper mount nut
Pull the wiring harness fastener back (just pushes on over the threads of the bolt) and take off the 4 nuts (two each side).
Towbar bolted on
Bolted on.
Towbar fits well
Now, time to use a hole saw to make a hole for the bolt that you mount the tow hook on.
Cut the grill!
Grill now has a hole.
And finally, thread on the tow hook/loop.
Tow hook finished

I think I will take the time to make a license plate bracket that can attach to this mount (when the tow hook/loop is off). Stay tuned.

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