Oil Cooler Duct: Prototype Testing to Final Product
So previously, we established that the oil cooler was the source of the high IATs, so Alex built a simple duct using CAD (cardboard aided design) to make a mockup, which we would install and test on the car. Due to the Golf R DSG having both bumper corners already filled with aux radiators (one for DSG, one for engine), we devised a plan to direct the hot oil cooler air straight under the car. Not ideal from an aero standpoint, but this is a relatively small volume of air so seemed like the lesser of evils.
Prototype duct built from cardboard to test proof-of-concept
Upon actually attempting to fit the duct to the car, he inadvertently discovered that the duct would not fit on the passenger side where the oil cooler was previously installed: The A/C refrigerant lines were just a bit too close.
Rather than redesigning the duct, we came to the conclusion that re-mounting the oil cooler in the center would actually be beneficial even without the duct for the following reasons:
The passenger side of the intercooler is the “cold” side. This means there is a higher Delta-T (difference in temperature) between the hot oil cooler and the cold side of the IC… meaning heat will transfer from the oil cooler to IC more efficiently (which is bad in this case).
When mounted in the center, clean air can flow around BOTH sides of the oil cooler to reach the intercooler as well. Whereas when passenger-side mounted, air would need to travel 2x as far from only one direction to fill that area. This would be beneficial for IC airflow regardless of duct or no duct (though potentially worse for making air go through the oil cooler, as this increases pressure on the backside of the oil cooler lowering the oil cooling abilities).
We performed street testing again with the cardboard duct, much like before when blocking off the cooler entirely. The following configurations were tested (in a similar test loop as was previously):
Center mounted oil cooler, no duct
Center mounted oil cooler, with duct but no hole cut in the bumper cover for venting. This would dump the hot air to a very small but concentrated area of the cooling stack, while somewhat restricting airflow through the cooler
Center mounted oil cooler, with duct and hole cut in the lower bumper cover to allow venting as designed. A small “chin spoiler” was added at the front of the bumper cover opening to encourage a low pressure zone behind and draw more air through the oil cooler
Here is a summary of ALL street testing performed, with details on each configuration:
Visual depiction of all variations tested
Stacked bar graphs showing IAT min + avg + max readings during 3rd gear pulls on the street with each oil cooler mounting/ducting configuration
The prototype duct final configuration ultimately netted a 59.5% drop in IATs vs the original passenger side mounted oil cooler with no duct.
Even more interesting was that our hypothesis on center-mounting the oil cooler proved true: Even with no duct at all, just moving the cooler to the center netted a 48.6% drop in IATs vs passenger side mounting (at least on the street).
Moving on, with the proof of concept done, fitment confirmed, and design street tested - it was time to send the CAD file out to be cut from aluminum for a more permanent solution, and move on to track testing:
Note that in the above photos, the lower opening of the duct was trimmed to fit once bumper was installed and excess trimmed off. It is not pictured, but a piece of the removed duct exit was added back as a small chin spoiler on the leading edge similar to further above during prototype testing. It is recommended to use duct tape or similar for attachment to leave this low hanging piece as “sacrificial” in case you hit some road debris, etc. It’s better to knock off the small spoiler than to potentially yank the entire duct and oil cooler with it.
Track Testing
In August, Alex was finally able to make it to the track for testing what we’d been collaborating on for about 2 months at this point. He made a trip up to Palmer Motorsports Park. Testing at VIR would have been more ideal to minimize variables, however based on collecting MANY logs from all over the country, IAT has a pretty concentrated range in which most aftermarket intercoolers will fall. We also lucked out that ambient temps were very similar (actually just a few degrees higher for post-duct-install testing).
It is important to note this test is NOT valid for comparing coolant or oil temperatures, due to the large difference in average speeds and average TPS between VIR and Palmer. So with that said, here are the results:
Over a full session, you can see how IAT continues trending upwards with the original mounting configuration vs the ducted configuration
And similar to how all my cooling data logs are done - this was a 200 second snip from the highest heat portions of each session for comparison purposes
Add this duct to fix YOUR problems!
Alex was kind enough to release the CAD files for free. It is licensed for your use under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International Public License.
Basically, you can use it, modify it, build off of it, but you can’t commercialize it and your derivative work must be licensed under this license as well. This was made and publicized to help the community, not make a buck.
CAD files 1+2+3 are the individual parts that must all be cut and assembled together. This was designed specifically for the Setrab 19-row Series-6 oil cooler. You are free to modify the CAD files to fit whatever oil cooler you want, but if it is not Setrab part number 50-619-7612, then it will not directly fit.
Link to the Notes, CAD files, and License Information HERE
This CAD file can be sent to www.sendcutsend.com to be produced just like he had done.
0.063" 5052 Aluminum is recommended as the material to be made out of. For reference: it cost about $95 cut, bent, deburred, and shipped (as of 08/23/23). You will need a BUNCH of 3/32 x 1/4in pop rivets to assemble. Just get a 100ct package. Be sure to read the notes document in the above Google Drive folder, and know that it will involve cutting a rectangular hole in your lower bumper cover for the air to escape.
