View Full Version : 03 SVT Cobra IRS Upgrade

12-16-2006, 05:17 PM
Why wait until something breaks! Tim and the crew at Modular PowerHouse http://www.modularpowerhouse.com replaced all the internals on the beast’s IRS this past Friday, December 15th.

I have included web links to most of the products and services. I’m sure you all have them already, but there may be someone just getting started with Mustangs, and it may help. Some of the parts seen and described were from previous installs.

I do more open track events than 1320 runs so I decided to go with a Detroit Locker TrueTrac carrier – part # DTL913A561. http://www.detroitlocker.com
I spoke with Detroit Locker Tech Support and they stated the TrueTrac does not have to be machined for C-Clip axles such as the ones in the IRS. They have a 45 degree lead cut so the axles can be inserted, the C-Clips put on, then pulled back against the housing. It has fixed bias and is a really good diff for autocross and open track days – at my skill level. I don’t drive at a level that would require a Torsen T2 (Type B) or T2-R (RaceMaster). Those are also a lot more expensive. http://www.torsen.com
The TrueTrac does not have clutches and is supposed to be strong enough for an occasional trip to the drags. I was led to believe that Torsen carriers are not all that happy on the 1320. I picked what I felt was a “best all around” carrier for my driving style.


I like the way 4.10 gears wake up a 4-valve. I had them in my MACH1. They make it easier for me to stay in the power band. So I went with a FRPP ring gear and pinion set. The gears produced the following RPM ranges in my Mustang:

Factory 3.55 gears – 70MPH = 2,050RPM 75MPH = 2,190RPM 80MPH = 2,350RPM
FRPP 4.10 gears –--- 70MPH = 2,370RPM 75MPH = 2,540RPM 80MPH = 2,720RPM

All readings were taken from a Stuart-Warner digital tachometer while in sixth gear. http://www.sw-performance.com
I felt this was a representative sampling, and did not take additional readings. It appears that the RPM change increases by 20 to 30 RPM per 5 MPH increase in speed past 70. Don’t know if that is true throughout the entire range of speeds. I keep up with gas mileage, and will be monitoring the expected change. I dropped about a half mile per gallon in the MACH1, on average. It was a five speed. Will be interesting to see what the six speed Cobra does.

This is how the gears looked when I got them.


I spoke with Dan Evans of Evans Performance Products in Cumming, GA. http://www.evansperformance.com
They are a full service coating operation; powder coating, ceramic coating, and REM® to mention some. They also do a cryogenic treatment on metal parts. I saw their ad in Grassroots Motorsports. REM® coating is a chemical treatment that makes steel parts look like they have been polished. Dan did a full Cryo-REM® treatment on the ring gear and pinion. Basically they take the parts down to minus 325 degrees for 12 hours. That’s the cryogenic part. It is supposed to stress-relieve metal and increase the useful life. Then they put the parts into a large vibratory machine with ceramic chips that look like small, light brown rocks. For all you reloaders, it looks like a vibrating case cleaner/polisher, only it’s about 4 feet tall and 6 feet across. They add a chemical to the vibrating mix that bonds to the metal over another 12 hour process. This process does not change the tolerances, and produces a finish that looks like this.


Smooth and “polished” bearing surfaces should produce less friction. That generates less heat, and should also help increase part life.

Based on the Cobra being a daily driver with track duty every now and then, I went with The Driveshaft Shop’s Level II half-shafts. http://www.driveshaftshop.com
I don’t think I will ever push the horsepower past their rated limit – 600 RWHP. But, if I ever get it to hook on a really sticky track I think they will still get me home without a tow. The half-shafts arrived looking like this.


I took the Detroit TrueTrac and ring gear to Modular PowerHouse a day early. I wanted them to mount the ring gear and let the thread locker set up for 24 hours before the installation. This is the ring gear mounted on the TrueTrac.


I arrived early on Friday and the first thing the crew did was pull the entire IRS system out of the car.


Then Andy, Brandon, and Bobby started taking things apart.


While it was out, I took a picture of the cross bracing they built for me during a previous installation. In the picture you can see the Maximum MotorSports full-length sub-frame connectors and the Kenny Brown jacking rails. http://www.maximummotorsports.com http://www.kennybrown.com

Tim welded in some custom cut steel tubing between the two rails to tie them together for additional strength and rigidity. It was a really nice job and I like it! Hind-sight is always 20-20. I might have gone with the Kenny Brown Extreme Matrix System when I first started modding the Cobra three years ago, but it would not work with the MM sub-frames that I selected back then. I like what I ended up with. You can also see a little of the Bassani mid-length headers and exhaust system, and the Maximum MotorSports 4-Point K-Member brace. http://www.bassani.com


Brandon started taking the IRS system apart.


When he got things apart, the Ford Carrier and 3.55 ring gear looked like this. You can see one of the Steeda urethane differential bushings still in place. http://www.steeda.com


Andy mounted the bearings and new races and had the TrueTrac ready to install.


The TrueTrac only had to be put into the pumpkin twice to get the shims correct. When Andy was done, he said the backlash was “perfect”.


Andy and Brandon put the pumpkin back into the IRS and installed the new Level II half-shafts. Three pictures below show the work in process. The close-up shows the short stubs which are kept from the factory setup. The rusty looking tubes with the ABS exciters contain the “tripod” that allows flex in the axle shaft pieces. In the side view you can see the Maximum Motorsports urethane IRS bushings.




They finished the re-assembly and in the picture below you can see the Steeda Differential Cover Brace.


Once everything was back in place, I took a last couple of photos before the tires went on. The first is a picture of the Steeda IRS brace that is welded to the IRS, and then bolted to the body.


The last shot is the FRPP drive shaft safety loop. Obviously its’ not tightened down yet. I figured now was a good time to install one while everything was apart. Andy said that Kenny Brown designed that piece for FRPP years ago, and he liked it better than some of the others they install. Not having a preference, I went with their recommendation.


Thanks to Tim, Andy, Brandon, and Bobby of Modular PowerHouse for an outstanding installation. As always, I am very pleased with the quality of their workmanship.

I took the Cobra out Saturday to do the recommended break-in on the ring gear and pinion. Drive sanely for 10 miles and let it cool for 30 minutes. Did this three times as the instructions stated, then put the drag radials on it for a ramp run to see what the “seat of the pants” meter said about the new arrangement. I really couldn’t hit it too hard though. Because they had to pull the IRS tie-rods and camber bolts, I will need to take the Cobra in for a full alignment next week.

But right now it’s hard for me to see the keyboard over the grin! I am looking forward to track season next year.

I hope you found this interesting. Thanks for taking the time to read through it.

12-16-2006, 06:14 PM
Looks great man, good luck with it. :thumbsup:

12-17-2006, 09:12 AM
Wow, that was a great write up. Congrats and best of luck!

12-17-2006, 10:47 AM
nice, enjoyed all the pics.

12-17-2006, 12:17 PM
:thumbsup: Nice. Good reading.

I have read about the cryogeinic/chemical process but did not realized it was available outside of the aviation field. It is supposed to increase strenght as well as make the parts wear resistant. They have been using a similar process in jet engine parts. What a difference that made on the ring and pinion.