We would like to take some time to show the heat exchanger system development we have had going on for the C6 Corvette ZR1 platform. We originally started looking at the platform while doing intercooler brick replacement design (which is still in testing), we noticed that the system as a whole had many shortcomings. We threw around some ideas and decided to go ahead and begin development of a complete turn-key HX solution. Looking at the OEM system, other aftermarket offerings, and speaking with ZR1 owners, we quickly came up with a list of design goals.
1. Design a more efficient heat exchanger setup for better cooling without sacrificing air flow to the radiator.
2. Increase fluid flow through the system.
3. Increase fluid capacity in the system.
4. Come up with an easier way to fill/check the system.
5. And of course we wanted to make the complete system of the highest quality of materials while keeping it as aesthetically pleasing as possible.
Some of the tools that we used during the R&D process included 3D modeling software, a 3D printer, a MoTeC C185 stand-alone logging system, MoTeC/RaceGrade K-type thermocouples and pressure sensors, as well as water flow and air speed meters. Data collection consisted of: bench testing, dyno testing, and in car track/street testing.
Some of the heat exchangers we had on hand to test for development were the factory GM HX, a Katech direct drop in HX, and a PWR or more commonly known as the Magnuson HX. Upon inspection of the factory HX, a large flaw was found immediately, there were no separators within the end tanks to force fluid through the core, allowing the potential for fluid to bypass the core and water tank. The heat exchanger also used a factory hose connection size of .464” ID for fluid entry which later proved to be a huge restriction in the system. The core itself has a very high fin density, and is a decent size with a frontal area of 142.62 sq in, at .875” thick, giving it a total core area of 124.79 cu in. and has a “tubes per square inch” ratio of 3.15.
Next we started looking at the Katech HX. This unit is a direct replacement for the OEM unit. It featured the same .464” ID fluid entries. This core was also missing the dividers in the end tanks. If you pour fluid in the top it runs out the bottom. The core frontal area was less than the OEM unit, bringing it to 130.50 sq in. The core thickness was right at 2.25” giving a total core area of 293.62 cu in. The fin density was less than OEM with a “tubes per square inch” ratio of 3.00. One thing we noticed is when the unit is installed, it pretty much blocks off all the condenser/radiator area above it. In hot climates like here in Houston Texas, this could be an issue.
We then evaluated the Magnuson HX, a sticker on the side showed it to be manufactured by PWR. This core was not a direct drop-in; it required custom brackets to be made for mounting in front of the condenser as well as line adaptions. It also had a very large frontal area at 320.62 sq in, but only had a thickness of .750” giving a total core area of 240.46. This core had a fin density close to the Katech with a “tube per square inch” ratio matching the OEM at 3.15. Fluid entries into this unit were a standard .750” with a .612” ID. We saw this as a definite improvement from the OEM entries. This unit was also built as a dual pass configuration which feeds from the bottom. There is a bleeder at the top and with the HX in the vehicle it is not accessible. It requires the HX to be lowered out of the air duct for bleeding.
After careful design and core selection, we built our HX with a frontal area of 194.06 sq in, with a thickness of 1.50”. This gave us a total area of 291.09 cu in with a “tubes per square inch” of 4.00. We were able to build it to fit the very front of the vehicle using the full width and height of the front opening, where 100% of the air would have to pass through it. The next step was to increase fluid flow through the system to help remove heat more quickly. We achieved this by reducing all restrictions in the fluid system (except the intercooler bricks themselves) and coupling this with the Stewart EMP pump in its reprogrammed (High Output) form. All lines and inlet/outlet sizes were increased to 1.00” ID to match the pumps ports and to lower total system pressure; thus maximizing the flow potential of the pump.
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The largest restriction we had to tackle besides the intercooler core itself was the cast inlet log manifold that feeds the intercoolers. This uses the same connections as the OEM intercooler, again with the .464” ID, but feeding both intercoolers. We sat down and designed individual feed inlets for the intercoolers, with .625” .750”, and .875” O.D. Barbs. Next, we 3D printed the different versions with our in house 3D printer so we could bench test them. Bench testing consisted of pump differential pressure testing while running fluid through the stock inlets, and our different test pieces, using the OEM joiners that connect the inlets to the intercooler bricks and back out to the pump (isolated). Testing showed the least pressure running the .875” OD barb inlets (these are true .750” ID). Once that was taken into account we tested the complete OEM system, including the lines, HX, water tank, factory inlet log, and intercoolers, to get a baseline of pump differential pressures and water flow rates. We then installed our upgraded inlets and retested. Next we swapped over to the EMP pump and tested. Finally, we swapped in our heat exchanger, large line setup, and dual stage recovery tank system. We were able to see how much each of these components affected flow and by the end of our testing we were able to almost double fluid flow through our purpose built complete HX system.
The last set of bench tests we performed were to measure air flow loss through the heat exchangers themselves. This was an important test as too much air flow loss will reduce the cooling ability of the radiator. The first HX tested was the OEM unit with an air loss of 16%. Second, we tested the Katech with an air loss of 18%. Next was the Magnuson/PWR, as expected with it being so thin, it had a minimal airflow loss of 9%. Last, we tested our D3 HX. This gave us an air loss of 16%, which was dead on even with the OEM HX.
