Diff's Hot, Take it Easy - Rear Differential Cooler R&D, Part 3: Track Prep

Diff's Hot, Take it Easy - Rear Differential Cooler R&D, Part 3: Track Prep

When you're hurtling towards a concrete-walled turn at over 90 MPH, you'd better know that every nut and bolt in your car is torqued to spec.

Photo: Nick Thomas

We've all had to prepare for something before"a date, an interview, a test. It's always a stressful experience. Now imagine you were about to go on a date with somebody you were pretty sure is trying to kill you. Or, imagine that your desk would be pushed off a 100ft cliff if you failed that test. Preparing for a track day is a lot like that.


About a week before our Focus RS was set to tear up Raceway Park's road course, Dan and Eric were neck deep in tasks. We would be pushing the RS to its limits to test our rear differential cooler; every box had to be checked and every part ready. A week isn't a lot of time to install diagnostic equipment, maximize the car's performance, finalize prototypes, and safety check the entire vehicle, but it all had to be done before 6:00 AM on Tuesday.


Before they could start prepping the mechanical, Eric and Dan first had to make sure the RS's notoriously finicky computer was happy. The RS sat atop our Dynojet, straps running from the frame to steel latches reinforced into our warehouse floor to hold the little beast still while its strength was maxed out. Eric was able to run the engine through the RPM ranges and gears that he'd be using the most on the track, filling our facility with crackles and pops from the exhaust.

Eric monitored the car's fueling system and adjusted as needed to get the most power out of the RS, while keeping within the AWD system's limits. Reliability and consistency would be key to get the most accurate data during testing. Our whole day would be ruined if the ECU and AWD system threw a code at the track.

Once Eric was satisfied with how the car was behaving, he pulled the RS off the dyno, and back onto the lift. That lift would be its home for the next week as everything from brakes to the contents of the glovebox were scrutinized.


The next steps in the prep process were to get the mechanical workings of the RS in order, install and wire diagnostic equipment, and safety check every part of the car. Each of those steps entailed its own list of tasks that would have covered our prep board three times over. Luckily, many hands make light work, and many hands we had. A big project like this requires seamless teamwork between planning and hands-on work. If your hands weren't full with another project, you were called on to take up a task from The Board.


If the car was going to have any chance of surviving the amount of abuse we would be putting it through, Eric needed to get started right away. There was plenty of work to be done from front to back, engine bay to wheel wells. One of the first projects was to route the coolant hoses needed for various sensors and the PTU cooler. In most vehicles, running a coolant line is a pretty simple task. In the RS, however, the coolant lines that we needed to access are crammed in between the subframe and the intake manifold. Eric also needed to drill the intercooler and add a bung for a temperature sensor. So, the intake manifold, along with the front bumper and intercooler, came off.


While Eric worked on the mechanical aspects of the car, Dan began work on wiring the mass of tendrils that made up our monitoring and data logging system. About ten sensors were responsible for relaying a mountain of data from the RDU and PTU coolers. To store all this data, we needed a reliable logging system mounted in the car itself. We couldn't risk losing data from a faulty wireless system.

Photo: Nick Thomas
Photo: Nick Thomas

Product testing data typically gets recorded via an AEM AQ1 data logger. The AQ1 allows us to wire in several sensors and collect their data, all in one log. We run and store these logs on one of our engineering laptops for analysis later. Because the AQ1 can only monitor a finite number of sensors, two AQ1s would be needed for this test. That meant we also needed two laptops to record all the data. Of course, those laptops needed power, along with several GoPro cameras. All that equipment, plus a fire extinguisher, had to be mounted securely enough that it wouldn't fly across the car when Eric decided to get a little sideways around the track.


Luckily, the hatchback practicality that makes the RS so popular presented us with a great solution. Dan and Eric folded the rear seats down and used the open area to build a mounting board for our laptops, AQ1s, power supplies and fire extinguisher. They traced out the shape of the hatch area and cut a sheet of thick MDF to match. Dan could then plot all the component locations he needed and fabricate mounts for each piece. The laptops would be held in place with a simple L-bracket and clamps, while the power supplies, fire extinguisher, and data logging equipment could be bolted directly to the board.

With the component locations determined, Dan wired the sensors and the power supplies. I make it sound easy, but this process took both Dan and Eric the better part of the week to complete. All the while, there was still a long list of work to be done to have the car ready for Tuesday's track day. In between mechanical prep, Eric stepped in to lend a hand with wiring and mounting the electronics. Meanwhile, other smaller tasks were distributed to those who had free hands.


One of those small, but important, tasks was to wrap the RDU ducting in heat reflective tape. While the production version of our ducting will withstand the heat emitted from the coolers and the abuse of any rogue rocks, our test pieces were 3D printed in PLA for time and cost savings. PLA can be fragile and has a relatively low melting temperature. The heat needed to be kept at bay and the ducts required some support. With Dan and Eric chained to the RS, one of our drafters, Riley, stepped up. With a little instruction from Sensei Eric, Riley made sure the ducts were thoroughly protected from heat and any possible road debris.

Photo: Nick Thomas
Photo: Nick Thomas

Of course, no track build is complete without a good set of wheels and tires, or two. We wanted a lighter wheel than stock. We also needed a stickier tire to maximize grip. To meet those goals, we chose a set of 18x8" Enkei YS5 wheels wrapped in 225/40R18 Toyo Proxes R888R tires. Knowing how hard we would be driving the RS, coupled with Eric's propensity for getting a little sideways, we picked up a second set of wheels and tires just to be on the safe side. After picking up the wheels and tires, Pat, the project manager, taped the wheel weights to prevent any from escaping at high speed.


Pat also took some time to complete one of the most important tasks on the list, one which took our team from humble small company, to a league accompanied by the likes of Ferrari and McLaren: branding the fuel jugs with our signature Mishimoto "M". It wasn't easy, but Pat made it happen and ensured nobody at Raceway Park would mistake us for anything but the top-notch racing team that we were.



Monday afternoon had come and gone. With the fuel jugs branded, ducts protected, wheel weights secured, and The Board rendered orange with completed tasks, it was time to put the final touches on the RS. Eric finished up the mechanical tasks by replacing the brake pads along with bleeding the clutch and brakes. The AEM systems and power supplies were wired and functioning, with a bit of carpeting completing the component board. All that was left to do was take the car off the lift and scrub the new tires.


Photo: Nick Thomas
Photo: Nick Thomas

At 5:30AM on Tuesday morning, I rolled out of bed, donned my black and orange Team Mishi shirt, and headed to the office to take part in one of the best workdays.


Thanks for reading,