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Now that we have a prototype E46 radiator, what should we do with it? Test it of course! The data for this entire build is based around radiator testing. Check out the report from our lead engineer.
BMW E46 M3 Radiator Testing
Test Vehicle Modifications: Supercharged, intercooler, methanol injection, full exhaust. Professionally tuned @550 whp on pump gas.
Cooling System Upgrades: 13-row oil cooler for supercharger located behind the kidney grilles. Front-mount intercooler (FMIC) located in the front air dam. Upgraded clutch fan that spins faster than stock clutch fan.
Additional notes: 100% pure distilled water was used for all tests. Stock radiator was in good condition with no debris clogging the core.
Testing Conditions: Temperature range 82˚F–85˚F and 70% humidity
Testing Location: Orlando Speedworld, 3/8 mile oval track, in Orlando, Florida
Apparatus: For temperature monitoring Mishimoto chose the PLX sensor modules driven by the Kiwi WiFi plus iMFD. This is a wireless system from the sensor modules to an iPad or laptop computer. The software used was the Palmer Performance Scan XL pro, which has full data logging capabilities. Sensor locations were installed inline with the upper and lower coolant hoses.
Mishimoto engineers wanted to test the new Mishimoto radiator in short-track and low-speed track conditions to determine the impact of the increased density of the radiator core. Engineers needed to confirm that the radiator would push enough air through the core to cool the engine and not cause overheating. A dense core design rejects more heat in a higher-speed environment, so testing the radiator in a worst-case scenario was paramount to confirm effectiveness.
Core Information: Compared to the stock core, the Mishimoto core has several changes to improve the conductance of the radiator. Improvements include decreasing fin height, which allows for more coolant tubes, increasing fin pitch, which aids in heat transfer, and increasing overall core thickness. The two figures below represent these changes. Overall capacity in terms of volume for the stock radiator is 0.65 gallon, while the Mishimoto radiator showed a 25% increase to 0.87 gallons.
Track Scenario One
First we drove a few laps around the track to get the engine and tires warmed up. Next, we drove full-speed laps for about 7–10 minutes, or until the temperature data reached a stable condition. Since the track is an oval we can explain the details of a lap fairly easily. For a typical lap under scenario one, Mishimoto engineers chose to run the car in 3rd gear for the entire lap. The straight section would see an acceleration from 3,000 rpm to 5,000 rpm, or about 40–58 mph, then hard on the brakes down to about 35 mph. As we passed the apex, the car was given partial throttle up to about 40 mph out of the bend; then we accelerated again up to about 58 mph, braked, and repeated. The graph below shows the results of testing for about five minutes of driving under these conditions. The temperature data from both radiators show that the car can handle this type of driving without any issues. Oil temperature under these conditions was approximately 233˚F as observed from the stock gauge.
Heat rejection is approximately equal for the stock and Mishimoto radiators under testing conditions for the first scenario. This is expected due to the governing laws of thermodynamics, i.e., energy output of the engine into the cooling system equals heat rejected from the radiator when under steady state. Figure 9 shows a difference of approximately 200 Btu/min, or 6% between the stock and Mishimoto radiators. The difference in total error is due to a combination of lack of testing repeatability and lack of sensor accuracy.
Scenario One Results
Both the stock and Mishimoto radiators were able to stabilize temperatures under the conditions stated for this scenario. One important difference to note is the reduction in the engine output temperature. For the stock radiator the engine output temperature was 195˚F; for the Mishimoto radiator the engine output temperature was 185˚F. Using this information we can calculate the air-to-boil (ATB) temperature. The ATB temperature is the maximum ambient air temperature reached before the engine outlet temperature of coolant will boil, which would result in overheating and engine failure (see Figure 10). For scenario one, the outside ambient temperature would have to be 140˚F for the stock radiator to overheat, while the Mishimoto radiator could allow an ambient temperature of 150˚F before overheating.
Track Scenario Two
First we drove a few laps around the track to get the engine and tires warmed up. Next, we drove the car at full speed using only 3rd gear for 7–10 minutes, just as we did for scenario one. Since the track is an oval we can explain the details of a lap fairly easily. For a typical lap under scenario two, Mishimoto engineers chose to run the car in 2nd gear for the entire lap. The straight section would see an acceleration from 4,200 rpm to 7,800 rpm, or about 40–62 mph, and then hard on the brakes down to about 35 mph. As we passed the apex the car was given partial throttle up to about 40 mph out of the bend; we then accelerated again up to about 62 mph, braked, and repeated. The graph below shows the results for about five minutes of driving under these conditions. This driving condition was extreme for the car, so we ended the test after about four minutes of driving. Oil temperatures for the supercharger were extremely hot, and oil began to seep and bubble from the oil pump. Engine oil temperatures were approximately in the 255˚F–260˚F range.
Inlet temperatures for both the stock and Mishimoto radiators were 2˚F–4˚F hotter than the respective outlet temperatures. Although the temperature difference between the inlet and outlet was slightly less than in the first test, flow rates of the water pump increased with engine speed, and the heat rejection for both radiators resulted in about the same rate as seen in Figure 9.
Scenario Two Results
Heat rejection for both the stock and Mishimoto radiators seemed lower than what the engineers expected. After some calculations the engineers found that the ideal heat rejection from the stock and Mishimoto radiators for both scenarios would be around 6200 Btu/min and 7400 Btu/min, respectively. This Q ideal or theoretical number would indicate perfect conditions, for example: airflow through the radiator core would equal the vehicle speed, and flow of both the coolant and the incoming air would be distributed equally throughout the core. Engineers concluded that the losses from the FMIC, AC condenser, SC oil cooler, pusher fan, and other shrouding lowered the incoming airflow to the radiator by a significant amount. According to the test data, average measured track speed for one lap was 42 mph. Engineers found that airflow was 19 mph instead of the ideal 42 mph. Other losses came from the presence of the FMIC and oil cooler, which increased the incoming air temperatures that enter the radiator, resulting in a lower rate of heat rejection for the radiator.
One additional note worth mentioning is the recovery time of the radiator after the hot lap. Immediately after the test we began cool-down laps by cruising around the track at about 40 mph to cool down the engine. For the stock radiator we needed about 2–3 minutes before the temperatures would return to about 190˚F, while the Mishimoto radiator needed only about 1.5 minutes. In hindsight, engineers should have recorded rather than merely observed this information. If we test the radiator again, we will be sure to gather this additional information.
Mishimoto engineers calculated that the test vehicle heat output was 3,700 Btu/min for scenario one and 5,500 Btu/min for scenario two. In scenario one the 550 hp car was able to maintain temperatures with the coolant, engine oil, and supercharger oil. In scenario two the vehicle was not able to maintain a stable condition. The engine output (5,500 Btu/min) was higher than the radiator heat rejection (3,600 Btu/min). This means that it would be only a matter of time before the car would overheat. For scenario two, the supercharger oil and soon-to-be engine oil overheated before the radiator did. Scenario two was an extreme environment when factoring in all the conditions: extra 250 hp vehicle, FMIC, supercharger oil cooler, and very low-speed track. (Note: This is why oval track racecars use such large radiators.) Mishimoto engineers calculated that the Mishimoto and stock radiators would have needed wind speeds of 32 and 36 mph, respectively, to reach the front of the radiator so that scenario two conditions could be maintained.
The Mishimoto radiator is designed for higher speeds but still outperformed the stock radiator in all tests, proving that the newly designed Mishimoto radiator will be an improvement over the stock radiator under all conditions. (Note: Performance will vary depending on vehicle modifications, environment, racing environment, and coolant type.)
Special thanks to Precision-Sport Industries located in Winter Park, Florida, for donor vehicle and shop space.
Now that we had successful testing results for our radiator and fan setup, it was time to follow-up with our original goals and be sure we did not miss anything with this project.
- Provide a direct-fit performance replacement radiator that functions with the factory mechanical fan.
The Mishimoto radiator bolts into the factory radiator position and functions perfectly with all factory equipment, including all engine bay shrouding. Use of both mechanical and electrical fans is possible with this radiator design.
- Radiator should have larger core capacity and thickness compared to the OEM unit.
We made a ton of improvements with the Mishimoto radiator compared to the factory unit. Check out some major points below!
- Coolant surface area increased by 32%
- Air surface area increased by 15%
- Coolant capacity increased by 25%
- Heat rejection increased by 6%
- Collect proven performance data on a high-horsepower vehicle under extreme driving conditions.
We traveled to Orlando, Florida, and collected hot-weather testing data on a 550 whp supercharged BMW M3.
Secondary Goal – Offer an electric fan conversion kit, and test the results of mechanical fan removal on power output.
Although this project is still being developed, we have a general plan for the electric fan conversion. We have proven the effectiveness of our fan-mount system for both cooling and power output.
Well, that’s it folks! Development has concluded for this radiator and we are on to the next project. Keep an eye out for testing of that oil cooler you saw in one of the earlier images. Thanks for following along and feel free to reply with any questions or comments.
Additionally, we are running a Group Buy for this radiator. Please visit the link below to sign up!