Tested: GrimmSpeed Subaru Top Mount Intercooler

GrimmSpeed Subaru top mount intercooler tested MotoIQ

Tested: GrimmSpeed Subaru Top Mount Intercooler

by Wes Dumalski

Around here we appreciate quality and well thought out parts that fill a void in the marketplace. Regardless of company size or the expanse of their market reach, it is refreshing to see a company and its collective mindset introduce a product that doesn’t re-invent the wheel but goes a long way to making it much more efficient. In this case that company is GrimmSpeed and that product is their Subaru Top Mount Intercooler. 

Having been dwelling in the horizontally opposed world as of late I have found myself helping with other EJ projects to learn as much as I can. While I will do my best to limit the hatred I have for some areas of this motor, I can tell you that people LOVE their boxer rumble and top mount intercoolers! While I may not share the same love of the noises these things make, I can say that the TMIC certainly has its advantages within this package. Of course we can debate the superiority of a FMIC in terms of cooling efficiency; however that is not what this article is about. In the case of the EJ, it provides nearly zero IC piping length as well as ease of packaging. It also places the IC out of harms way up high in the engine bay and not stuffed low and up front. For street driving, the TMIC does a decent job of cooling and for many of the people modifying this platform, a quality TMIC is all they will ever need. 

Case in point is a 2004 STi project that I have been working on with a friend and this car is what directly led our interest in the GrimmSpeed TMIC. To set the stage a bit we were in the process of converting the fuel system on this car using the Injector Dynamics ID1000 top feed conversion kit as well as the Walbro 400LPH pump to huff the corn (E85 to us non-cool people). The goal was to take this car to the limit of what the factory VF39 turbo could offer in terms of performance. Aside from the typical aftermarket downpipe and exhaust, the car was also fitted with a Tial 38mm external wastegate through the use of the GrimmSpeed EWG up-pipe. From an intake perspective the car uses an SPT intake along with GrimmSpeed Ceramic Coated TGV deletes. While we are not in any way saying these modifications are required we wanted to share the details of the car we were using to put the IC through its paces.

GrimmSpeed Subaru TMIC Intercooler MotoIQ Test
Fresh out of the box is our GrimmSpeed Subaru TMIC. In addition to the clean construction each IC is inspected, cleaned and sealed prior to shipment. 
It’s quite clear that Justin Grimm and Matt Beenen started completely from scratch when they designed this TMIC. While there are other intercoolers on the market for this platform, there was a void in the performance per dollar category and they sought to fill it. While there are quality IC offerings at the $800 + price point, there is very little available offering an extremely high performance design cheaper than that. With the target set they began by selecting a core. In this case they are using a 19” x 7” x 3.75” bar and plate core chosen to strike a balance between reducing pressure drop and maximizing heat transfer.  Our measurements show a total core area of 498.75 cubic inches in comparison to the OEM 2004 STi TMIC which is 352.24 (18.5” x 7” x 2.75”) and the largest OEM Subaru TMIC from the 2008+ STi at 387.5 (20.875” x 6.75” x 2.75”). This makes the GrimmSpeed 140% larger than the 2004 TMIC and 120% larger than the 2008+ piece. We ONLY took measurements from the OEM STi TMIC models as the WRX units are laughable and frankly, in comparison, are a waste of both your time and ours. 

GrimmSPeed intercooler core bar and plate

The bar and plate core was chosen to achieve proper fin density to maximize heat transfer and minimize pressure drop. The measured pressure drop was .16 P.S.I. at 19 P.S.I. 
GrimmSpeed cast end tank TMIC intercooler SUbaru mpreza WRX STi
Here is a shot of the inside of the Grimmspeed end tank. Attention was paid to the radius at each end to produce the most efficient design possible. 
The GrimmSpeed piece also uses custom designed permanent mold cast aluminum end tanks. If you are familiar with casting methods you will know that this process ensures greater accuracy from piece to piece with the tight tolerances required for this type of product. This also provides the designer greater flexibility when designing the contours of the inside and outside of the end tanks when compared to other casting methods. The idea is to produce the highest performing intercooler possible that still fits within the confines of the EJ equipped Subaru engine bay. It also appears that all flanges and mating surfaces are machined flat after casting and the sturdy IC mounts are designed to accept the OEM rubber isolators to mate to the factory mounting brackets.  They are also slotted to allow for plenty of movement and tweaking for proper fitment. The TMIC is designed to use the OEM STi Y-pipe or GrimmSpeed offers their own cast aluminum version. The end tanks are designed to interface with the OEM bypass valve and use the same outlet diameter as the OEM piece. Lastly GrimmSpeed use stainless threaded inserts to provide a stronger connection instead of threading into aluminum.  
In the interests of making their creation as efficient as possible they also designed a hood mount splitter to replace the OEM piece, which features larger diverters to better distribute air across the core. They also include a rubber gasket that ensures a proper seal between the splitter and the TMIC. Also available is a thermal dispersant coating and STi Y-pipe kit. 

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