Top Contender – Street Performance Top-Mount Intercooler R&D, Part 1 – Concept and Design

“You know cars, right?” I’m sure that’s a question that all of us gearheads have been asked before. It’s typically the wind up for a pitch to help them find the car that’s going to suit every one of their specific needs, which usually looks something like a combination of reliable, fun, and gets good gas mileage. Oh yeah and it snows like once a year so all-wheel-drive is a must. Their budget is around $30k. I know what you’re thinking, a 2013 BMW 328i xDrive hits the nail on the head, but I know most of us would point this friend to the obvious choice—the WRX.

Since 1992, the Subaru has made a name for itself by mixing these characteristics into the affordable WRX. Granted, we didn’t see this trim until 2000, but it’s no surprise why it immediately took off and became a staple in the enthusiast community. The trademark growl that came with the turbo-boxer engine powering all four wheels was enough to make anyone feel like they were driving a world class rally car.

When it comes to the latest iteration of the WRX, we might not have that classic rumble anymore since Subaru ditched the unequal length headers when they changed up to the FA20DIT, but some things remained. The pistons are still horizontal, and all 268 of those horses are still put down to all four wheels with the help of a twin-scroll turbocharger. The charged air running to the cylinders is also still cooled by an intercooler mounted to the top of the engine instead of in front of it.

To help with the overall shape of the new design, Jason uses our Faro Design Scan Arm to create a 3D model of the stock intercooler along with the space around it. Having a digital slice of this part of the engine bay means that the owner can still cruise around in his WRX while Jason works on improving the intercooler.

As far as intercooler placement goes, Subaru is one of the few manufacturers that still places the cooler for the charged air at the top. It does have its advantages, of course. When using a top-mounted intercooler, you’re no longer obstructing the rest of the cooling system, plus you minimize pressure loss since (especially with this unit) the cooled air is dumping directly into the throttle body. Not to mention, you now have the perfect reason for a fully functional, and mean muggin’ hood scoop.

It’s almost as if the WRX has an extra nostril that’s specifically for keeping the charged air cool.

Even with its own dedicated channel of fresh, cooler-than-engine-bay air, the stock unit was developed with the good-enough sort of mentality that leaves one wanting more. With tens of thousands of these WRXs on the roads, it would significantly increase the price of the car out from under that $30k range if each one had a heavy-duty intercooler installed. Instead, Subaru used a lightweight, tube-and-fin construction for the core design, with plastic end tanks to shepherd the charged air to the cylinders. Both aspects are easy to mass produce and will perform well under typical commutes, but the stock core design will struggle once performance maps or tunes are introduced.

Core thickness and internal volume are always specs that stand out when it comes to an intercooler. For a stock unit, this intercooler is actually pretty thick. We still see room for improvement, though.

Being a top-mount, this intercooler is going to need all the help it can get. Since the WRX is a staple in the enthusiast community, it’s uncommon to find these not sporting tunes or MAPs to crank up the boost. This isn’t good for the inherently smaller heat exchanger, and this unit has to contend with the residual heat from the engine bay since, you know, heat rises.

For the best perspective on fitment, we created the framework of our new intercooler design using metal piping and 3D printed versions of our end tanks.

That’s where Mishimoto comes in. We’ve already been hard at work improving on the top-mount design. Our engineer is maximizing the available space to give the core a significant increase in size. On top of that, we’ve started from the ground up when it comes to our end tanks to ensure a smooth flow to and from the core.

It might not seem like it at this stage, but our design will have a significant size increase over the stock unit.
We even maintained compatibility with the factory engine cover, and have plans for including our own ducting for those who prefer to run this intercooler without the engine cover.

After ensuring that our bigger core with the new end tank designs would fit under the hood of the WRX, we spared no time getting testable samples from the R&D facility to ensure the gains over the stock components. We also wanted to check our work against the challenge of different tuning options, so make sure you stay tuned (see what I did there) to see how our new top-mount design performs on the WRX.

Thanks for Reading!

-Nick

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