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S550 The Rented Mule Build Thread Profile - S550 Mustangs

Exp. Type
Exp. Level
20+ Years
North Central Illinois
Here we go! I’m a relatively new guy around here, but was lurking for quite some time. Back in Dec '21, someone posted here about the sale of the Ford Performance Racing School ("FPRS") GT350 Track Attack cars and asked if anyone on TMO bought one. I figured that was as good of a time as any to join the forum and my first post was on that thread. I'm the proud current caretaker of #14, aka “The Rented Mule”, which spent the first six years of its life as a working steed at the FPRS – first at Utah Motorsport Campus in Tooele, Utah and then at Charlotte Motor Speedway in Charlotte, NC. Through this build thread, I'll share the ups and downs of buying and tracking a cast-off school car. So, strap in and hold on tight – hopefully this will be an interesting ride!

This is my third GT350 – the first was H2614 (’17 Shadow Black) which I bought new, but traded-in eighteen months later for JR265 (’18 Magnetic base model R – now owned by a good friend). It’s also my second former school car – the first was a 2001 Bondurant Mustang GT (which also stayed nearby as another friend owns it these days – and recently upped its game with a Coyote / T-56 swap). I guess I sorta see these old school cars like lost puppies looking for a good home.

I began wheel-to-wheel racing in the early ‘90s, then switched to autocross / time trials and eventually track days as they became prominent. I also volunteered with NASA as an instructor for a few years before taking a long break from on-track fun to build a Factory Five Racing Cobra replica and do some restorations. I really enjoyed the FPRS Track Attack experience and learned just how capable these cars are with only a few basic mods. When I attended, I paid for the extra insurance and proceeded to flog the car, but never reached its limits in the controlled environment of the school – although… ahem…. there was that one little off-track excursion through the gravel at the south cross-over when I turned in a bit early at Agony (east course). When asked by friends if I enjoyed the program, one of my first comments was: “I beat on that car like a rented mule.” Now, that’s not entirely true, as I like to think I have a fair level of mechanical sympathy. I went away impressed with the GT350s capability and, although I’ve often regretted selling JR265, I knew I’d be back on track someday – and with something I could use as blunt-instrument sort of a tool.

Me and #14 in the "Attitudes" at UMC - Oct '18.....


After twelve years away from the track (except for some touring sessions and a couple of actual events), I got back in the market for a track car in early '21. I looked at many alternatives, but as a committed Ford fan I kept gravitating back to Mustangs and GT350s. Having missed the sale of the Boss 302FPS cars in late ’19, I reached out to FPRS and asked if they’d be selling off any others in the future. My persistence (and constant pestering) paid off when they called in early November and offered me dibs on #14; the same car I drove when I attended the Track Attack program at the end of the ’18 season.

Although I planned on having it shipped, logistical challenges arose and I ended up making the twelve-hour drive to Charlotte with my open trailer to bring #14 to its new home. I’m glad it worked out that way, as I really enjoyed the trip - absolutely beautiful weather (especially for the first week of December). When I arrived at the school, the FPRS team were very welcoming. I spent a couple hours checking things out, getting loaded, and ransacking the left-over GT350 program items in the gift shop. Having only been to the Utah location, it was nice to get a chance to check out their current digs. The drive home was beautiful – taking me through the mountains of southern and western NC and eastern TN – with my little 4Runner doing an admirable job, thanks in large part to my small and light trailer.

Loaded up and headed to its new home......

Ready to Leave CMS_12.2.21 (2).jpg

I’ll be using the Mule exclusively for track days and time trials. So, this is a work-in-progress story of buying, maintaining, developing, and running the car. My initial focus was on making sure it’s safe and reliable for this first season. As a baseline, it’s in great shape, especially for having covered just over 16k miles on track in the hands of many, many drivers of, shall we say, widely varying skill and sympathy levels. The mods done by FPRS were minimal and pretty much what most owners who regularly take their car to track-days would likely do, including:
  • Gen 2 replacement engine - apprx 4k miles ago;
  • Watson Racing bolt-in 4-point rollbar
  • Safecraft harnesses for front seats (no anti-sub straps)
  • OEM Ford rear seat delete panel
  • ARP wheel studs (long) with open lug nuts
  • Caliperfexion front brake studs
  • Removal of the rear seat belts and front belt connectors
  • Maximum Motorsports camber plates
  • Castrol SRF high-temp brake fluid
Overall, it’s the perfect starting point for this sort of a build with absolutely zero surprises so far – in fact, it’s exceeded my expectations. So, in addition to the work done by FPRS, I've added a few things already this season, including:
  • Ford Performance springs and sway bars;
  • Steeda adjustable end links;
  • Replaced the stock Recaro seats with a Sparco Pro ADV (driver) and a Pro 2000 (passenger) on Planted brackets w/sliders;
  • Added anti-sub straps to the FPRS 4-pt harnesses;
  • Swapped the OEM wheels with MPSS tires for a square 19x11 set of Apex SM-10 wheels (w/25mm spacers on the front) and Pirelli DH slicks (305/690/19);
  • R splitter;
  • Ford OEM "swing" updated rear spoiler;
  • KohR / Multimatic GT4 canards;
  • Vorschlag brake cooling deflectors;
  • FP350S-style lower radiator opening brake cooling duct extensions;
  • R exhaust with heat wrap at diff (no valve motors - safety wired open);
  • R and late non-R grill with additional opening at airbox inlet;
  • Tow rings;
  • Air/oil separators;
  • Removed A/C belt;
  • Gutted trunk;
  • Wider air vent slots in front inner fender liners w/protective screens on front to protect oil and transmission radiators; and
  • Track alignment with camber initially set at -2.3f/-2.2r;
It's been a great season so far with a few more events to go. I started out at Road America in May, followed by Autobahn full-course, and then a recent run to Gingerman with the Team Shelby group as they kicked off their "Dearborn Invasion" event that coincided with the Woodward Dream Cruise. Soon the Mule and I will be headed south to Barber Motorsports Park, then another round at Road America before finishing the season out at Blackhawk Farms. The Mule will continue to see action and be developed into a more focused track weapon, but through it all, it’ll continue to rock the FPRS livery so that it’s always identifiable as a part of GT350 history.

I hope you'll follow along with us on the journey.

15 (2).jpg


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Exp. Type
Exp. Level
20+ Years
North Central Illinois
East of DeKalb - near Kaneville / Elburn.


Cones - not just for ice cream
Exp. Type
Exp. Level
20+ Years
Congratulations on scoring a school car! Sounds like you've made some judicious upgrades and should get miles of smiles from The Mule.

Funny seeing that cone at the top of Attitudes. When I did my Boss Track Attack in 2014, I had all 4 tires on the second stage of the rumble strip there. If it's paved, it's track, right? :hellyeah:
Exp. Type
Exp. Level
20+ Years
North Central Illinois
Today, we find the Mule experimenting with something seen at the recent Gingerman event.

Special thanks to @Black Boss for this one - a Lexan cover for the airbox. Besides the obvious advantage of keeping clag and rain out of the airbox (once I vent the hood), I'm hoping to see a drop in intake air temps.

I haven't ventilated my hood yet - still on the fence as to whether I'll get an aftermarket carbon hood or cut the stock one - but I wanted to give this mod a try. My goal was do to it with as little modification to the airbox as necessary, just in case I don't see any improvement (or it blows out - LOL) and I decide to go back to stock or take some other route, such as removing the factory seal and bolting the Lexan in place or one of the aftermarket covers.

I ordered a piece of 2'x2'x3/16" Lexan (polycarbonate) for around thirty bucks, which was enough for two covers - I can probably even get a third out of it if I'm creative with placement. The 3/16" thickness was a bit of overkill - if I do it again I'll just use 1/8".

Template -
I started by making a template out of cardboard. The rough dimension is 14"x16", but the finished version is just a bit smaller than that.


Cutting -
Although the Lexan comes with clear cling on it, I added a layer of tape to protect it from the hand-held jigsaw I used to cut it.


Securing tabs -
In the pic above, you'll notice a small tab at the bottom. on the left side, and at about the 2 o'clock position - I used these to hold the cover in place down inside the factory hood seal after making three small slits in that seal.


Finished -
The Lexan cover is just a bit oversized so that it's a tight fit down in the rubber seal, which has a ridge that holds the cover in place - this is where 1/8" thickness would probably be a better choice. The tabs add a bit of extra security, as I'm concerned about what will happen at very high speeds when I let off on the throttle, closing the throttle body and resulting in high pressure in the airbox. As a bit of belt/suspenders/safety-pins engineering, I added a small bead of 3M strip caulk around the inner ledge of the airbox housing, and then pressed the cover down onto it, making a pretty good seal. The 3M strip caulk is non-hardening butyl rubber and withstands heat very well and cleans up easily with mild solvents, such as adhesive remover.


As you can see in that last pic, there is a bit of a gap where the foam sidewall doesn't quite meet up with the rubber seal, which I'm sorta figuring will act as a pressure relief for those times mentioned above.

The Mule's next event is at Barber Motorsports Park, so we won't be seeing any crazy high speeds, but it'll be back at Road America at the end of September, so I'll report back after that on how this mod holds up at 150+ when letting off the throttle approaching corner one.
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Exp. Type
Exp. Level
20+ Years
North Central Illinois
Just a short update from the Mule's 1600 mile road trip adventure to Barber Motorsports Park this past weekend.

The weather couldn't have been better, with moderate humidity and temps in the low 80s on Saturday (a bit warmer on Sunday). This was my first time at Barber and it lived up to the legend - what a beautiful and challenging facility. Chin put on a great event, running everything on-time and cleanly. As for me and the Mule, we enjoyed a best lap of 1:38.3, with the top three laps separated by just 2/10ths.

The only cloud on the weekend was that in the second to last session on Sunday, the wonky clutch finally decided enough was enough. What started as just an odd feeling of a "notchy" clutch pedal, which shouldn't be there on a hydraulic system, began to exhibit a stiff action on initial push and then it would hang in the down position for just a split second. Eventually, it just stayed on the floor, so I cruised to pit in and shut it down.

Since the transmission is coming out for some clutch work, I'm going to also install a new tone ring on the output shaft (sort of a deeper dive on the flange nut TSB) and install the MGW Gen2 shifter that has been sitting on the shelf.

Until next time - happy trails!

Mule and 74 Front Straight.JPG

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