Tested: GrimmSpeed Subaru Top Mount Intercooler


We were surprised at the results from the OEM TMIC after the averaged runs. Clearly heatsoak was the order of the day and the calculations showed us an intercooler that was roughly 45% efficient during the testing duration. Before anyone shouts out a different number this is representative of the results we saw with this testing method.  The most important thing is that the intercoolers were tested in the same manner, on the same day, without removing the car from the dyno. 

GrimmSpeed intercooler STI y-pipe tested motoiq
The optional Y-pipe is a cast aluminum piece that includes the necessary hoses and clamps.  While you can use your OEM STi Y-pipe we opted for the GrimmSpeed piece to make swapping the intercoolers easier during testing. This is also a nice option for those of you upgrading a WRX or Forester where you may not have the necessary OEM Y-pipe. 

Before the rollers had even stopped spinning we all dove into the engine bay to swap the intercooler. Everything was scorching hot and we certainly took one for team nerd while making the switch. All told it took us 10 minutes to make the swap and get the car back up and running.  This was not even close to being long enough to allow the car to cool to our original testing condition temps. so we went over our line routing while we waited for things to cool off.


GrimmSpeed intercooler test Six Star Motorsports a spec dyno. gangster tunedYou can clearly see how thick the GrimmSpeed TMIC is in comparison to the stock unit. The slotted mounting brackets make it very easy to get the intercooler aligned during installation. This is hugely important as many people will be using this intercooler with aftermarket turbos and other modifications that move a lot of these components around. 

Once we reached the correct temps, we fired the car up to take a quick spin on the rollers to check for leaks and ensure that all was well. We then repeated the same 4 pulls and preserved the time between pulls to keep things consistent in our testing. After extracting the data I had to triple check my numbers to make sure I was seeing things correctly. The calculated efficiency was roughly 70% which is clearly a huge improvement over the OEM piece. In addition to that increase, I was able to watch the data logger in real time between pulls.  I observed that the GrimmSpeed recovered more quickly between runs. We also deduced that while this is a fair and accurate test that we would likely see different #’s on the street at normal driving conditions. 

GrimmSpeed tmic tested dyno. Six Star Motorsports

We left the dyno with the above #'s. Our goal was NOT to produce maximum power, but rather to create a good usable power curve with a conservative tune. With the GrimmSpeed TMIC we were able to produce more consistent dyno #'s over multiple pulls as opposed to the OEM TMIC which would heatsoak, causing power to fall off, and knock to become more evident.

After spending a few hours on the dyno. we used our burnt fingers to pack up the car and headed out with the new tune with the idea of conducting the next part of our test on a day when we could swap the IC and do some street driving. When that day finally came we first logged the GrimmSpeed TMIC for a 30 minute drive of mostly daily driving pace with a few full throttle pulls here and there. We also logged at what point during the drive we went WOT and did our best to recreate that same duration by duplicating our driving path. We performed this route and duration with both intercoolers and sorted through some boring ass data sets to come up with our #’s. When driving like a law abiding citizen, both intercooler’s offered the same 76% cooling efficiency. This supported our theory that we would see a large increase in efficiency with the proper ducting and fresh air to the core and that when you limit boost and do not drive hard enough to heat soak the IC what you have stuffed on top of the engine matters less. 

GrimmSpeed intercooler installed Subaru STi WRX Impreza Forester

The GrimmSpeed TMIC in its natural habitat. The three F's are all fully present in this photo (Fit, Finish, and FUNCTION)! You can also see the hose that replaces the OEM hardlines for the head breathers. This was our temporary routing before we re-do all the plumbing on the car this winter. 

None of these findings surprised us in the least, they are on par with exactly what we expected save for just how useless the OEM intercooler becomes when heat soaked under hard conditions. After gathering our data we set out to compare to what GrimmSpeed offered the general public on their website. Call us arbiters or mythbusters, we just wanted to know how our separate testing compared overall. After looking at the provided data charts from GrimmSpeed I concluded that while their product is an awesome performer, they still presented an honest data set that during testing put their product at a disadvantage. It appears their data was collected when doing a test where the car was hotter at the beginning of the test with the GrimmSpeed IC versus the OEM IC. Regardless, the data shows that their TMIC is a large step in efficiency over the OEM unit. They also show you very clearly the areas where the OEM TMIC shows slight advantages, if that is not transparent then we do not know what is. 

The only other test that we were not able to perform was on a road course, however in an upcoming article we do plan to document the efficiency of this test car with the GrimmSpeed unit against our very own Gen 3. STi project. We will be doing this to compare TMIC to FMIC in overall efficiency as well as response, all in the name of science for our dedicated readers! Long story short, if you are in need of a QUALITY top mount intercooler for your 02-07 WRX, 04-13 STi, or your 04-07 Forester XT, then look no further than the GrimmSpeed unit.  It is quality kit at a great price. 

GrimmSpeed logo

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