Here’s A Look At The Engineering Behind That Subaru WRX EJ25-Powered Porsche 911 GT3

A Subaru WRX engine in a Porsche 911 GT3. It sounds like blasphemy to some, and brilliance to others, but to Faruk Kugay, a drifter representing the Devspeed Motorsports shop out of California, it’s just another challenge. He built an E30 BMW with an F20C Honda engine last year for SEMA, and this year the drift racer decided to go with something a bit flatter and mounted farther towards the rear. I stopped by his creation at SEMA the other day to took a close look, and was lucky enough to run into him; here’s our interview about the car’s basic mechanical setup.

Read Japanese oil manufacturer ENEOS’s press release about the Porsch-baru, and you might get the impression that we have a ready-to-rock racing machine on our hands, but if there’s one thing that became clear while looking at the Subi-powered Porsche, it’s that this project has only just begun. There’s no cooling system, the engine isn’t mounted properly, the shifter isn’t hooked up, and on and on — Kugay is only at square one with this build.

Here’s a quick look at ENEOS’s description about the car’s mods:

The goal was to create a track weapon. The EJ25 is 170 lb lighter than the original GT3 powerplant and can be modified to exceed the 911’s stock 415hp output. To that end, the ENEOS-lubricated STI engine was upgraded with a BorgWarner EFR 7064-C turbo and a massive Vibrant Vertical Flow intercooler. It was fitted with Deatschwerks fuel injectors, rails and pumps, which draw from a Nuke Performance fuel cell and fuel system. By adding a custom exhaust system, Faruk was aiming for 550hp, which will be transmitted to the rear wheels through the Impreza’s six-speed transmission with a reverse-cut ring gear and bellhousing from Subarugears in Australia, assembled by SubiWorks in Murrieta, CA.

With the GT3’s competition future, DevSpeed sourced GT3R racecar bodywork from VAD Design in Great Britain. Not only does it revive one of Porsche’s muscular competition cars but the expansive fenders accommodate huge 19×10” front and 19×13” Rotiform 917 wheels, which themselves are fashioned after a legendary Porsche design.

Putting the power to the pavement, the ENEOS GT3 was equipped with extremely sticky Toyo Proxes R888R tires measuring 265/35 R19 front and huge 345/30 R19 rear. These DOT-approved competition tires are designed to give the driver full control in extreme driving situations including road racing and track days.

That makes it sound a bit like the car is built, doesn’t it? That the engine is ready, and the tires are already chosen. But that’s not really the case; and I’m not criticizing that fact! I’m just clarifying the point. Anyway, let’s get into what’s built, how it’s built, and what still has to be done to make this thing a reality on the drift-course.

The car began as a Porsche 911 GT3 that had been wrecked, and that Kugay’s friend had purchased from auction site Copart so he could use the engine and transmission for his other vehicles. Kugay bought the remaining shell and decided to make it the platform for a drift car, spurred by visions of a 911 GT2 drift machine he remembers seeing “back in the day.”

Of course, since he works with Japanese oil company ENEOS, a Japanese motor was in order. “All the weight is on the back axle Having a high center of gravity is a really bad thing,” Kugay told me when describing his rationale for choosing the Subaru EJ25. “If we’re doing a flat-six,” he said, “why not go back to a Mezger?,” he said referring to the stock GT3 mill. Thus, with a desire for a flat, non-six-cylinder engine, Kugay chose the EJ25 turbocharged 2.5-liter four-cylinder, in part, because it’s lightweight.

Let’s Talk About That Engine

EJ25s aren’t known for their longevity when built to make lots of power, so that’s what had Autopian writer Thomas Hundal concerned when he saw that Kugay’s goal was 550 horses. “This is a mock-up motor,” Kugay made clear when I voiced my skepticism. “I’m getting an IAG closed deck magnum block. You gotta do that. If you wanna make 500 horsepower, you get a reliable motor.”

I’m fairly sure this is the motor to which Kugay, who admitted to me that he’s new to the EJ engine world, is using for the build:

Here’s IAG’s description of the nearly $13,000 “IAG 900 EJ25 Closed Deck Long Block w/ Stage 4 Heads”:

The IAG 900 package is ideal for clients looking for an engine package to support up to 900 BHP applications. The IAG 900 Long Block features our Magnum Closed Deck Short Block that utilizes a brand new EJ25 Subaru case that is converted to closed deck and is bored and honed to 99.75mm. The Magnum block features 14mm head stud machining, as well as our Fire-Lock™ gasket solution that is loosely derived from diesel technology where a counterbore step is machined around each cylinder bore allowing specially sized fire rings to drop into the machined area and head gasket bores.

IAG goes on, describing the pistons, rods, heads, and head studs, among other components:

The combination of the alloy compression shims and gaskets assure maximum sealing for a Subaru EJ25 turbocharged engine. The Magnum internals includes IAG-Spec JE FSR 2618 forged pistons, .250″ / .906″ H13 pins, IAG-Spec Tuff H-Beam +2mm connecting rods with ARP 625+ rods bolts and an OEM STI crankshaft. The block is then paired up with our Stage 4 Fully CNC Ported Cylinder Heads to deliver maximum flow for high horsepower applications. The heads start as brand new Subaru OEM cylinder head castings that are CNC machined and resurfaced. The heads are outfitted with GSC valve train components, consisting of +1mm oversized intake and SuperAlloy exhaust valves, Beehive Springs as well as your choice of GSC Billet Stage 2 or Stage 3 camshafts. To complete the package, we add an IAG / ARP 14mm head stud set and all the required gaskets for the final valve cover-to-valve cover assembly.

Anyway, that sounds like it’ll be plenty stout for Kugay’s Porsche.

But for the time being, there’s a mockup 2008 EJ25 motor in there; let’s just look at it for good measure, shall we?:

That’s the intake in red. Sitting atop it is a “Vibrant” intercooler, with a pipe running down from it to a turbo behind the rear bumper.

The Turbo/Intercooler Setup

Let’s go through how this turbo/charge air cooler circuit is plumbed. The exhaust is under the engine; it flows rearward to the turbocharger:

Here you can see that turbo just under the bumper:

Let’s get a little closer:

That exhaust spins up a turbine before exiting out of the rear of the car

.

The turbine is on the same shaft as a compressor, which sucks air axially into the turbo via what looks like a K&N air filter, and then pumps that air through the big silver pipes in the engine bay. The squeezed air enters the charge air cooler/intercooler on its left side. You can see the hose fitting on top left of the image below:

You can barely make it out in this photo, but the intercooler’s outlet it located at about its cross-car centerline, towards the front of the car; it points downward into the intake, where it sends the squished air to be consumed by that motor:

One thing you may be wondering is: “Where’s the fan?” Well, that’s at least what I was wondering, since the intercooler is mounted in such a way that it won’t receive ram-air. Kugay says his team still needs to do some testing. “We’re not there yet,” he said. “I think we’ll actually not have a problem with pressure drop.”

The Cooling System

If you were looking closely at the engine bay, you might also have noticed a lack of an engine cooling system, making you wonder if perhaps there are some hoses running to the front of the car, as would be normal on a rear-engine vehicle. Actually, nope, this Porsch-baru has no cooling system yet — just a hose going from the thermostat outlet, in a big loop around the front side of the engine, to the water pump inlet [Two edits later: Okay, so I definitely just glanced at this cooling system prior to writing this initially. As a reader pointed out, I completely got it wrong, so let’s just go through it]. 

This EJ25’s cooling system has no heater or radiator. Instead there’s a hose simply running in a loop from the crossover tube on top of the engine to the thermostat inlet on the bottom.

Yes, this is a thermostat inlet, not an outlet like I’m used to seeing on the older cars I work on.

Located on the bottom of the engine, this thermostat inlet housing that the hose connects to (via some quite elegant AN fittings that Kugay’s team welded on) is fastened via two bolts to the engine’s water pump. That’s right: The thermostat and water pump are integrated into one assembly; it’s quite elegant (see below). The black cover you see above hides the engine’s timing belt that connects the crankshaft to the camshaft sprockets on both heads. This belt is what drives the pump.

You can see what the motor looks like without the timing cover in the image below from the Subaru service folks at Subieguys:

You’ll notice in the photo before the one directly above that the water pump features three ports inboard of where the thermostat would sit. One is for the heater return line, one is an oil cooler return line, and I think one is a return from the coolant expansion tank.

Anyway, the point is that coolant flows — normally from a radiator — into a thermostat housing, through a thermostat, and into that water pump at the bottom of the block. At that point, the water is pushed through the block, outboard through both cylinder heads, then back from each cylinder head into the top of the block, out of these two outlet ports:

Mounted to those outlet ports in the block is a coolant manifold, or crossover pipe like this:

You’ll notice the two inlet holes (each mounted to the block and receiving coolant from a cylinder head) and two outlet pipes — one to the radiator and one to the heater core. Here’s a look at the crossover pipe’s radiator outlet, which Kugay welded an AN fitting to, and which he — as mentioned earlier — is running straight to the thermostat inlet housing on the water pump at the bottom of the engine:

So in short, water flows through a thermostat at the bottom of the EJ25, into the water pump, then gets shoved through the block, then through the heads, then into a crossover pipe at the top of the engine. Then it flows to the heat exchangers (heater core, radiator) and back into the water pump.

Obviously, I just “black boxed” the entire cooling path through the metals, and since I’m not about to deprive you of that knowledge, check out the SubaruONLY videos above detailing how water flows through the motor itself. Here’s a screenshot I labeled showing the right side of the engine block — cylinders two and four.

Anyway, that was a long way of saying that this Porsch-baru has no heat exchangers.

Kugay says the plan for the cooling system is to cut some vents in the hood, roughly where the inside of the U-shaped yellow graphics on the hood are (see above), and then to duct air out of that hole.

Kugay’s team cut the front of the GT3’s tub in order to fit the cooling module, which will receive ram air, aided via fans, and shoot that ram air through the ducts in the hood. The advantage, there, is that the ducts will reduce the pressure on the back side of the cooling module, encouraging airflow. What’s more, it reduces cooling drag, since the ducted path is more aerodynamic than the underhood, where most cars shoot their radiator fan-blast air.

The ducts will work just like these in the fenders, which vent air in the wheel arches to reduce drag:

The Engine Mounts

Let’s talk about the engine mounting scheme. Kugay will be the first to tell you that it’s not where it needs to be quite yet.

The flat-four is currently mounted, via the factor Subaru motor mounts, to a suspension crossbrace. I’m fairly sure these brackets pointed out here are where the motor mounts up:

The plan, Kugay told me, is to change that setup, and make a girdle/engine plate that incorporates the factory rear mounting locations on the body; you’ll notice that those provisions are pretty far rearward compared to the end of that short four-cylinder motor, so those will be some sizable mounts:

The way I understood it from Kugay is that the team mounted the engine and six-speed Subaru manual transmission, set it up so the axle lined up, and established the transmission mounting location. Now that it knows where everything will sit, the team will go back and build proper engine mounts.

The Subaru Transmission Converted To Two-Wheel Drive

We should probably talk about that transmission a bit. Normally, on a Subaru WRX, the engine is up front, and the transmission sits behind, sending power both forward and rearward, since the WRX is all-wheel drive. Per Kugay, the transmission has been modified with a reverse-cut ring gear, a block off plate in the rear, and a solid center diff. “Spins the other direction” he told me.

The way I understand this: Imagine a front-mounted Subaru WRX engine with a transmission bolted to the rear of it. Now spin it 180 degrees about the Z-axis and move it to the rear axle. Now the engine is in back of the car, with the transmission facing the front. In drive, the formerly-front-wheels-but-now-rear-wheels and formerly-rear-wheels-now-front-wheels would want to propel the car in five-gears worth of reverse. Put the transmission into reverse, and the car could go forward, but only in that single gear.

I think what Kugay’s team has done is gut the center differential, and block off via a plate what was formerly the rear outlet and is now the transmission outlet facing the front. So now what was formerly the front axle is the only one getting power, and to reverse its direction so there are five forward gears instead of reverse gears, the team modified (or plans to modify) the now-rear differential. At least, that’s how I understand it. (I don’t know what Kugay means by “reverse cut” in the video, as my understanding is that this doesn’t actually reverse direction).

Shifting happens via a custom shifter made by an “old guy” named Jim, per Kugay. You can see how two cables run from it to the passenger’s side of the transmission sitting in the “back seat.”

The Interior

I won’t spend too much time talking about the interior, since once again, I find myself writing geeky car stuff late on a Friday night instead of doing, you know, things that normal single dudes do. But this is important stuff! So let’s look at this oddly square-cross-sectioned steering wheel, which I quite like:

Kugay, who very specifically noted that he prefers 360mm steering wheels, says his “buddy Bob” developed the steering wheel above by water-jetting out different layers, and welding it all together, before having it wrapped in a rubbery cover. The result is a cool vintage shape, but with a pistol-grip-style outer ring. It’s great.

Kugay also mentions the digital gauge cluster and single-piece 3-D printed dash, which was apparently done backwards and not sanded enough, hence why it’s a bit imperfect. But still: anything this big and single-piece 3-D printed has my respect:

Link PDM/dash

Kugay also pointed out the impressively-tight roll cage, which Illumaesthetic helped design by scanning the 911 GT3’s interior. Cage kits is the one who built it:

Kugay pointed to the floor, where he had welded in some Nuke Performance, large-diameter-piston, low-pressure air jacks, which are there to allow for quick servicing during racing.

Among those quick services is tire-changing.

Wheels And Tires

The gold 19×10-inch front, 19×13-inch rear Rotiform 917 wheels are beautiful, and feature 265-section rubber at the nose and 345 tires out back. Those are Toyo Proxes R888R’s, though Kugay indicated to me that these might just be the tires used for testing, while the main drift-racing tires might be something different.

Steering the front tires will be the stock 911 GT3’s steering rack with hydraulic lines running to it from a Cup Car electrohydraulic steering pump, since Kugay doesn’t plan to mount a pump to that EJ25.

Here’s a guess at the pump the drift team might be using. Seller Achilles Motorsports says it’s “OEM equipment for the Porsche 997 911 Cup Cars.”

As for what’s sending power to those rear wheels, that’s going to be Porsche axles adapted to that Subaru six-speed manual. Per Kugay, the way it will work is, the Subaru’s transmission output will feature an adapter (presumably like the shafts below), which will mate up to the 930 CV part of the Porsche axle. So if I have this right, each rear halfshaft will be part-Porsche (outboard, plugging into the wheel hubs) and part Subaru adaptor shaft (inboard, plugging into the transmission).

That’s pretty much all I know about this build right now. Clearly there’s a lot of work still to be done, but I love the concept, and I look forward to following Faruk Kugay on his Instagram and YouTube platforms to see what kinds of engineering solutions/compromises he’ll have to implement to make it all work.

Photo credit: AIG Engine photos via AIG Performance. All others: David Tracy.