Like many before me, my installation uses a pair of 25-row Setrab Series 6 heat exchangers, plumbed in series using 10 AN flex hose and the OE thermostat. Where it differs from any other installation I have seen is that my heat exchangers are mounted vertically, and I have incorporated actual inlet and outlet ducting. In all the off-the-shelf kits I have seen ducting seems to be very much an afterthought.
Mechanical Installation
The primary structural element securing oil coolers is a plate sandwiched between the bumper crash beam and the chassis. This method is very simple and easily carries the vertical and lateral loads.
The plate also serves for mounting an exit plenum that closely fits the fender liner. By mounting the cooler somewhat ahead of the fender liner, there is room for a plenum which allows for an orderly exit air flow.
The oil cooler is secured to the plate via vibration isolating grommets and aluminum channel sections. A stay connects to the bumper crash beam to react fore/aft loads. The resulting installation is very solid.
Plumbing
Plumbing is typical 10 AN flex hose with reusable AN and 22 mm Boss fittings. I have incorporated a tee in the lower interconnect line that allows for full drainage of the system (the branch being capped off at the moment but intended to permit connection of an Accusump down the line). At the oil filter housing I am using Hard Motorsports AN adapters (not impressed - I recommend spending more on any other brand).
Exit Plenum
Whereas the OE installation places the oil cooler hard up against the louver (and calls it a duct), my installation does actually provide a plenum/duct. I like the OE louver design because it protects the oil cooler from grit thrown up by the tires.
LH Exit Louver
Unfortunately BMW doesn’t make a comparable LH louver, so I made my own by trimming the flange off a RH louver.
Then I welded a mirror image aluminum frame.
The louver element was then bonded in place. The resulting LH installation is mirror symmetrical to the OE RH louver.
Design Principles
A basic design principle for ducting heat exchangers is to expand the inlet air (with a diffuser) to reduce its velocity and increase its pressure at the face of the heat exchanger, and then contract it to increase its velocity and decrease its pressure at the exit. A rule of thumb (and the one I followed) is to have an inlet area of 20% of the radiator core area, and an exit area of 25% of the radiator core area (conveniently the OE louvers provide this). For the inlet to work well, the expansion must be gradual enough not to result in flow separation in the duct.
Intake Duct
My inlet duct went through many iterations. Many models were printed on card stock, cut out, assembled and tested for flow characteristics. The final configuration was fabricated from TIG welded 0.050” 6061T6 aluminum.
I will follow up in a later post with some details of the testing process, and how the duct design ended up as it did. The ducts are identical on the LH and RH side of the car, which is somewhat convenient. I have previously described my brake cooling duct modification. As part of this installation I also built a new lower radiator/intercooler inlet duct. All three are visible in the following image.
I have had one track day since these modifications, and that was cold and damp, so not a good opportunity to see how effective the oil cooling is. That will have to wait for another day.
