Hot Rod cooling. Fun topic. First off I want to give a disclaimer…..this is what worked for me.
Also 90% of people do not need to harden their cars this much because you don’t beat on them as hard as I do. Many times I’m asked to take someones car out on the track to see what it will do and I over temp their car. Even if the owners never had an issue. I brake, corner and accelerate harder than most people. Ask my buddy Gordon. Oh he won’t let me drive his stuff anymore.
A car has two parts to it, track capability and track durability. Capability is lap time, maybe one lap. Durability is how long it can do it. At work we run test called “Tanks full of fuel”. We fill the car all the way up and run it flat out on a race track until the fuel runs out. We do these back to back. A vehicle with usually thermally stabilize after the 2nd tank fulls of fuel.
Most of us that take our cars to open track days run 20 minute sessions. These are usually about 40 minutes apart. So not as hard on stuff as what we test at work. If you just AutoX you will most likely not have any issues other than power steering cooling. Make sure for whatever you do make sure the power steering cooler is big enough. I now just use a oil to water transmission cooler built into the rad. C&R talked me into a smaller one on Jackass and I killer 4 power steering pumps before I went to a bigger cooler.
I have been fighting cooling issues for years. Most aftermarket products were designed to cool vehicle that cruise around or do occasional drag racing.
With the growth of Pro-Touring track events over the last 15 years the need to cool these cars has become apparent. I was an anomaly back in the ‘90 going to open track days and doing One Lap of America. When I rolled up to tech Brock Yates was amazed. He was correct, we did not finish and we did catch on fire! I learned a lot on One Lap.
As a little background on how I sorted some of this out. I was fortunate that my day job was developing high performance vehicles for GM at about the same time my Camaro started to get real fast. We would take a “Street” car to the race track and we would have all kinds of cooling issues.
It was during this time frame I came to understand not all cooling parts are created equal. Most of your “Hot Rod” radiator companies use cooling technology from the 70s. Have you hear the term “I have a 2 core radiator in this”. The OE to save mass, cost and add fuel economy have worked with suppliers to develop higher efficiency cores. (Heat rejection per square inch). The OEs are always attempting to balance the mass flow of air around and trough the vehicle. Cooling needs mass flow of air. But the more air you jam into the radiator and brake cooling duct the more the drag goes up. To help drag you can add better fans to move air without effecting drag. Hot Rods are just bad for areo put they do have a lot of cooling area.
To help the mass flow of air the OEs developed much better cooling fans that are controlled by PWM (Pulse Width Modulating) the fan. These fans (I use one from a 2019 CTS-V) can consume 75 AMPs at full power (About 1.2 HP). With modern controls the fan is driven off 3 parameters. Coolant temp, A/C head pressure and inlet air temp. So the fan only runs as hard as it needs to. We have all been at a car show and a great looking car rolls by and all you hear is his crappy fan whaling away.
A fan will cover up or help a car with poor front end air flow, or a thick cooling stack. First is packaging. My buddy Jack Chisenhall (Owner Vintage Air) told me a long time ago the radiator is most efficient on the top 1/3. On double pass cross flow radiators the hottest engine coolant is at the top. Make sense. I always leave the top 1/3 of my radiators uncovered by the intercooler or the A/C condenser.
The cooling issues real became apparent to me once I moved from naturally aspirated engine to supercharged engines. Some of my earlier cars could hit 320 oil temps in 3 hard laps.
My cooling stack has evolved like the OEs. If you look at the cooling system of a current CTS-V or a Camaro ZL1 it is a module. It comes out as a single system. Engine cooling radiator, Intercooler, A/C condenser and fan are an assembly. This system is isolated by rubber isolators to the body/frame. I have moved to the same system. My cooling stack weights about 60 lbs wet so it sits on radiator isolators from a C-6 Corvette and the mass is held by the sub-frame. It is constrained for-aft and cross car with more rubber isolators that go to the radiator support. On Gunner did not allow enough “float” and failed 3 radiators. As you must have sorted out by now it this is not a bolt in system.
Keeping with an OE approach I have all my heat transfer done in the cooling stack. I have C&R build me a one off radiator to my print. It has a nice high efficiency core. (They used to use OE Denso cores and have moved to an in house core). The engine oil cooler is a NASCAR part oil to water, it also has 2 more oil to water heat exchanges to cool the power steering and transmission fluid.
To recap power train cooling. You need good air flow to cool things. Open up the front end and or add very good cooling fan(s). Use a high quality radiator. Allow the system room to thermally expand and contract. Make sure it mounting will survive track use.
On a side note on power train cooling. On my supercharger cooling systems I have tried a few things. After testing a few things and talking to some experts at work I have concluded that the super charging air to water systems work the best if you can keep the system flow up. So I like to keep the head pressure down by limiting the hose lengths and bends. Let the water flow as efficiently as possible. Use good pump(s) and make sure you get all the air out of the system. Designing the system so it will “burb” is critical to get the air out. To test after the system is bled, turn on the intercooler pump with the engine off. The pump should run smoothly with no tone. If you have air in the system you will hear it go through the pump. For the ZR1s at work it can take 2 hours to properly bleed the intercooler system to get all the air out.
You asked about diff cooling. During the development of the Gen 1 CTS-V we could see diff temps above 320F in about 7 laps of our test track. (For reference most synthetic oils break down above 320F). So we set that as an excursion temp to not exceed). We struggled to come up with a cost effective solution to cool our diffs for production. Most solutions were loud and expensive. We also had an issue with manual transmission temperatures. We worked with Tremec to develop a pump for the TR6060 transmission. This killed two bird with one stone. We use the internal transmission pump in the TR6060 and the Automatics to pump trans through a cooling loop. The pump moves trans fluid to the radiator to an oil to water heat exchanger. The cooled fluid is then moved to the diff to a oil to oil cooler then back to the transmission. The aftermarket T56 Magnums do not have the pump built into them but the casting will except the pump. I added it to Hellfire. It was cool but expensive. D&D Performance can do the modification. Now I just use a Weldon standalone pump on a switch.
It was not until Gunner that I added a diff temp sensor. What I discovered on Guner was if you have GearFX polish the gears you can do three 20 minute track sessions before the diff temps get over 300F. I did not add a diff cooler to Gunner.
The new LT5 powered car I am adding a differential cooling loop because I know it will be an issue with higher power.
The key to sorting all this out is data acquisition. Now that you can get system like RacePak or other data loggers you can look at the data after a session. It is way too hard to monitor everything while you are driving. Now you can set flags in the digital systems to flash when things go outside preset limits.
Sorry this is long winded…. But you asked.
Brian Hobaugh SCCA National Tour June 2014
First Hemi 'Cuda Convertible Ever Built
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