2002–2007 Subaru WRX/STI Top-Mount Intercooler Part 5: Data Collection, Continued
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Mishimoto Subaru WRX/STi Performance Top-Mount Intercooler Kit
As mentioned last time, our team decided to make an improvement to our intercooler design. Because of the cast end tanks, we were left with a rather thick inlet. The wall diameter was significantly greater than what we would prefer, and opening up this diameter would only increase flow. The inlet was removed from the intercooler and an aluminum pipe was then welded on. This thin-walled pipe would provide significant benefits in overall airflow.
After finishing this modification we were prepared for more testing. Our next subject was a bone stock 2004 WRX. Obviously we would be dealing with less power than on the previous test runs. We were interested to see the effects of reduced power on the efficiency of the Mishimoto intercooler.
Our first test was the OEM WRX top-mount intercooler equipped with an aftermarket Y-pipe that we compared with the Mishimoto setup. Once again we averaged the runs and kept all variables as consistent as possible. It was interesting to see that once again the Mishimoto intercooler provided both horsepower and torque gains. Maximum gains were 10 hp/tq with average gains of 5 hp/tq across the entire powerband.
The STI cooler is a common upgrade to the WRX charge air system. We already had a cooler prepared for testing, so we decided to install this on the WRX and compare it to the Mishimoto. It was staggering to see that, with the STI cooler installed, this WRX actually ended up losing power. Although this might not happen with a modified WRX, the loss in power in a stock WRX was likely due to the larger volume of the STI cooler.
We also recorded AIT drops for all three intercoolers. The graph below shows an average drop in temperature of 4˚F compared to the WRX and STI coolers, which showed similar cooling performance.
Our next test vehicle in for testing would be a modified vehicle. After scouring the area for anyone willing to help, we found a kind enthusiast who had no problem helping us out. In rolled a 2003 WRX wagon, very similar to our shop vehicle but quite a bit nicer. The owner had done some minor modifications, including an 18G turbo, larger fuel injectors, large aftermarket top-mount intercooler, exhaust, intake, a tune, and 15 psi of boost.
I am a bit of an estate man myself (currently lusting after an old Volvo 240 or Mercedes W124), and this WRX was a great example, including some very nice chassis and suspension modifications.
This vehicle was already equipped with a larger aftermarket intercooler. It would be interesting to do a comparison of the two coolers to see the benefits of the Mishimoto unit. Unfortunately, we could not collect temperature data for these runs, because the owner of this vehicle was not interested in having his expensive intercooler drilled and tapped (I can’t blame him!). So for this particular test we collected only horsepower and torque data. After making consistent passes with each cooler, we compiled the data and the results are shown below.
Much to the surprise of the vehicle’s owner, the Mishimoto intercooler provided peak gains of 15 hp and 17 tq over his aftermarket unit. Our average gains were 10 hp / 10 tq, achieved from 3,750 rpm through red line. If this test-fit participant was not receiving this cooler for free (for allowing us to use his vehicle), I think he would have been first in line to pick one up!
Check back next time when we make a change to our intercooler core composition and perform a test on a high-boost WRX!