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C7 Z06 Cooling Development

C7 Z06 Cooling Development

Over the past two months or so, we've been working with Operations's 2015 Z06 Z07 to solve the overheating problems that plague these cars. This thread will detail our development efforts as we narrow in on a solution.

Since we're located at the Motorsports Ranch in Cresson, TX, we've got the ideal thermal testing environment literally in our backyard. For those of you not familiar, OEMs come here on a regular basis in the late summer to stress test cooling systems on track in the 100°+ heat. Our goal for this car is to run a full HPDE session at Circuit of the Americas without overheating. For us (and many other racers) that means more than just not going into limp mode. The car will run with water temps of 235° or more, but we don't consider that acceptable performance for a track car.

As detailed in this thread here ( the first step was a DeWitt radiator and oil cooler. While it made a difference, it was nowhere near enough to solve the problem.

To give a brief history, the car ran at COTA in Sept. 2015 in 100° weather. Water temps were north of 260° and oil temps were almost 300°. The car lasted 6 laps before it went into limp mode and came back in. That was with the DeWitt Gen1 radiator.

In Feb. 2016 in 70° weather, the car ran almost identical temps as the previous summer, but was able to go an extra two laps before coming in.

So while the DeWitt radiator is a step in the right direction, it's clearly not enough for a track car.

The first step in this phase was to install "cheek mounted" heat exchangers for the supercharger.

This involved cutting up the bumper, so for our trials we bought a new bumper so as not to ruin Operations' until we had a final solution.

We knew we were facing a significant challenge. At the risk of oversimplifying the problem, this car simply cannot dissipate enough heat for the power it makes. "X" amount of air entering through the front can only dissipate "Y" amount of heat, regardless of heat exchanger efficiencies, packaging, etc. That fundamental theory is why we chose the LG Motorsports kit.

To attempt to understand the behaviors of the myriad heat exchangers in this car, we set up an Aim MXL2 with eight temperature sensors throughout the engine bay to log various fluid and air temperatures.

We noticed a while back that the C7 Stingray has the same radiator (down to the GM part number) as the Z06. Doesn't really make sense, given the extra 200hp of the Z06, and is most likely part of the problem. So to increase the overall cooling capacity of the system, we added a second auxiliary radiator in front of the main radiator. This radiator measures 18" x 8.5". To monitor the performance of this radiator, we added water temp sensors at the engine inlet and outlet, as well as between the two radiators. We also are monitoring air temperatures in front of all the radiators, between the auxiliary radiator and main radiator, and behind the main radiator. With the two water temperature sensors monitoring the blower coolant temps, we filled up the 8 analog channels we had on the MXL2. It's not as thorough as an OEM's vast array of thermocouples, but we also have a small fraction of their R&D budget.

The eight sensors and extra heat exchangers were arranged like so:

We also fabricated and added a much larger reservoir above the intercooler pump to give it as much of a chance of success as possible, given the increased load. We're already worried about getting heat out of the system fast enough, we don't want to be fighting a cavitating pump. You can also see the two intercooler temperature sensor blocks in the lines just below the reservoir.

Once we got all of this installed, we went testing. We drove one session Thursday afternoon (6/30), but we were fighting the active handling and Ediff the whole time. We were never able to run a full lap "at speed," but we got some very useful data nevertheless. Here's what we learned.

Here's the engine coolant temps throughout the engine bay. The red line is coolant coming out of the engine, purple is between the two radiators, and blue is returning to the engine. You can kind of tell the temperature drop isn't split evenly between the two, especially considering the larger size of the main radiator. More on that in a sec.

Here's blower coolant temps. Same color scheme, red is coming out of the engine, blue is returning.

What was really interesting, though, was the air temps.

Blue is air coming in through the grill, purple is between the two radiators, and red is out the back of the main radiator.

To make things a little more easy to interpret, here's the water temp differential across all three. Calculated by subtracting outlet temp from inlet temp:

And air temp differentials across the main and auxiliary radiators:

Looking at those graphs, it's pretty clear the auxiliary radiator is hurting airflow through the main radiator. Although the overall cooling performance has increased, the total lack of air temp change across the main radiator tells us it's not doing near enough.

What's happening is the hot (235°) coolant is hitting the cool (95°) air coming in across the auxiliary radiator. When that happens, the air is heated up to about 180°, and the coolant is cooled to about 180°. The end result is zero heat transfer across the main radiator.

So for our next test day, we need to rethink how we're running coolant through the auxiliary radiator. It seems like the extra capacity is helping, but there's a lot of improvement left.

Previous article C7 Z06 Cooling development Part II

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