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

Wrx 911 4

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.

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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:

 

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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.

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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?:

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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:

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Here you can see that turbo just under the bumper:

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Let’s get a little closer:

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

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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:

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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:

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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.”

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The rear of the vehicle it the top of the photo.

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.

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

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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.

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image: promotiveconceptsllc/eBay

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

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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:

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

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Image: eBay/a1ofmiamiusedautoparts
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Image: eBay/a1ofmiamiusedautoparts

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:

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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.

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Screenshot: SubaruONLY

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

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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.

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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:

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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.

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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:

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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:

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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

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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).

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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

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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:

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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:

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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:

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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.

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Among those quick services is tire-changing.

Wheels And Tires

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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.

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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.”

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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).

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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.

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45 Responses

  1. I wonder why he didn’t mount the intercooler at the rear and reverse the intake manifold, greatly reducing the pipe length from the turbo and where airflow can be more easily managed. I’m not sure what he means by reverse cut here. I thought that usually referred to pinion offset as going either above or below the ring center. To change axle rotation, I would think he would have to locate the ring on the other side of the pinion from where it is stock.

    There were 2wd Subarus, though the old 5-speeds. They were basically the AWD unit without the center diff. Of course, I doubt anything is interchangeable with these much beefier 6-speeds.

    1. Check out Subarugears.com for pictures but we’ll have a video out on the transmission build in about a week.

      The conversion includes a new transmission bellhousing that puts the ring gear on the other side of the pinion gear. Remember in a subaru 6 speed transmission the output from the transmission feeds through the gears past the front diff and its ring gear then onto the center diff. The center diff then transfers the power back through a shaft back towards the motor to the ring and pinion for the front diff. Since our car is two wheel drive, we bought their block off kit which included a coupler that locked and eliminated the center diff, transferring all the power to the front diff. The reason I, and many, call it a reverse cut gear, is because it is in the reverse direction from its original construction. Subarugears makes a bell housing that adapts its placement.. and now the trans spins as a trans axle in reverse.

      The intercooler is there for several reasons. The surface are of the intercooler compared to the volume of air going in at our anticipated power… will be more than adequate for proper iat’s.

      1. I have a EJ20 turbo powered VW Beetle. Mine is using a VW transaxle with an adapter plate to mate the VW trans up to the Subaru engine. Almost 20 years ago when I started the project, there was a guy in Australia, Todd Triebler, who was on Aussieveedubbers forum with the idea to make a reverse cut differential for Subaru Tranaxles. He wanted to avoid the adapter plate method. In the aircooled VW world, you could spin the entire setup on the Z axis and simply flip the differential and install it so that you would have your gears putting you in the correct direction. The Subaru does not lend itself to this simplicity. Therefore, Todd did the research and development and created a differential and pinion that would fit the Subaru Transaxle and spin the opposite direction so that a front engine transaxle could be installed into the a rear configuration of a VW.

        1. Yeah, that’s what I figured must have been done and he had just used the wrong term. It otherwise doesn’t make sense. IIRC, old VW transmissions could be entirely flipped upside down for use in mid engine kit cars, which is the same effect.

            1. FV flip the ring gear… flipping the transmission would raise the engine a bunch, put the starter down low, and is actually explicitly against the rules. There are other SCCA classes (with different transaxles) that might do this, but not FV.

  2. While other automotive journalists go cool, weird and skim over to the next attraction, you have gone into to depth on this. An excellent read that shows how projects like this actually happen, thanks David.

  3. Achilles Motorsport electric steering pump = electric steering pump from a Holden/Opel Astra from the scrapyard and rebranded as “motorsport” lol. They are good pumps though and easy to hook up and use 🙂

  4. This ‘reverse cut’ stuff had me baffled, so I check out the Subaru Gears website.

    Basically, there is enough room in the case of the transaxle to install the differential with the ring gear on the opposite side from which it comes from the factory (after trimming some of the cast-in reinforcing ribs). When the ring gear is installed on the opposite side, it will turn in the opposite direction, so now the turned around transaxle will propel the vehicle with 5 forward and 1 reverse gears.

    I’m thinking the OEM pinion and ring would still mesh, but since they are gears that are cut on an angle, they would apply a thrust load to the transmission in the opposite direction from the OEM installation. Therefore, in order to maintain the same thrust loading directions on the transmission, the pinion and ring gear need to be replaced with a pinion and ring gear of the ‘opposite hand’ (or as called ‘reverse cut’).

    That ‘reverse cut’ is just bad terminology (disclaimer: I don’t know squat about transmissions and differentials). I think right hand / left hand is easier to understand.

  5. I suppose to really appreciate this, you would have to have torn down and rebuilt the stock 911 engine. Personally I hold an A&P rating, which allows me to rebuild aircraft engines, piston & turbine. Not too easy to get this rating a lot of background training required. I did rebuild my own 911’s engine and realized what a kludged together POS it really was. There were so many failure points it left me speechless. Now years back, while at UCLA I was engaged to the Porsche distributor’s daughter. Her father confided to me that the main selling point to the 911, as determined by the marketing guys was; the sound it made. At the time fully 50% of worldwide Porsche production was sold in SoCal. It was one of the few places where you would ignore the persistent leaks, lousy ventilation and actually poor cornering performance (seeing you never really get much above 25mph due to traffic). The Subi is popular to retrofit in a lot of vehicles, light and compact. Couple that with being relatively cheap to acquire. It has its issues with head leaks, but overall much better engineering then the Porsche.

    1. There a lot to unpack in that response.

      Better is a strong words. Lighter is definite. We’ve built old mezgers, water cooled mezgers and IMS engines at the different shops I’ve worked at. I’ll tell you this, subaru motors are cool, but they don’t rev to 9k (easily)

      As of now, we plan on using the IAG block w/ 14mm head studs with our existing 2008 heads. Quite a more reasonable option than was listed in the article.

  6. I guess that I am beginning to lose my “competitive” instincts, but I fail to find a compelling reason for this thing to even exist. For some very marginal gains, these builders have spent a ton of money to accomplish what has already been accomplished.

    What is the actual purpose of this thing?

    1. I’m excited out of raw curiosity. Mainly how it differs from the stock GT3 – how does the powerband change? How does the handling change? Will it be more or less forgiving with a lighter engine in the back?

      Mainly, how does the feel of the thing change? Calculations and CAD are one thing, actual driving experience is another.

    2. “I wanna go fast”? In the words of a great racer

      It should be significantly lighter and more powerful than a cup car. We will see. Or it could be a colossal waste of money… either way… should be fun

    1. Until someone wants another one, yes! Haha.

      We do have some 997 cup cars that live at other shops at Sonoma Raceway though. It would be interesting to see a side my side comparison when we get this done. Weight/track time/power.

      Our shop, DEVSPEED, is at Sonoma Raceway btw

  7. The water pump pulls cooled water thru the thermostat?????

    Most every car I’ve ever worked on sends hot water out thru the thermostat, not in. Seems like it would never open if it’s trying to draw cold water thru it all the time. The idea is that the water in the block/heads heats up opening the thermostat sending hot water to the rad to be cooled, right?

    1. We’ll follow which ever direction the water is meant to flow through an EJ… as I said… we’re not there yet. Its a very easy switch. Logic implies that water exits the thermostat location. We’ll utilize Vibrant weld on -16 an bungs to the factory Porsche aluminum lines, and run them to a large center mounted radiator… just like the RSR’s did.

    2. The key to the function of the water pump inlet side thermostat location is the return from the heater core. The Subaru EJ engine vehicles do not use a water valve, so the heater core is always flowing coolant whenever the engine is running. Coolant from the crossover tube (which has been heated by the cylinder heads) is sent to the heater core and it returns to the back side of the thermostat, which exposes the T-stat’s wax pellet to the warming coolant as the engine warms up. In this way, the heater core coolant circuit acts as the thermostat bypass – otherwise, there could be no coolant circulation through the engine until the thermostat opens. When the heater core return coolant is hot enough, the thermostat begins to open which begins to allow flow through the radiator. A thermostat located on the inlet side of the water pump generally gives better control of coolant temp during engine warmup compared to the traditional outlet side thermostat. Quite a few modern engines have inlet side thermostats. Even some Chrysler stuff had it (2.7/3.2/3.5L LH cars, Jeep 3.7L V6 & 4.7L V8) although that stuff was out before David worked at Chrysler so he might not be familiar with it.

  8. That’s an interesting project. The cooling system labels in the photo are backwards, though. The thermostat housing is the coolant inlet to the engine, and the pipe on the top of the block is the coolant outlet from the engine. Trust me – I work for Subaru. It would be interesting to see how the cable shifter is made to work on the STi 6-speed transmission which has a rod-type shift system in stock form.

      1. Hey David, your EDIT needs correction. You have the direction right now, but the thermostat at the bottom is bolted to the water pump which is turned by the timing belt. What you have labeled as the water pump at the moment is the coolant crossover pipe that normally takes hot water to the radiator. The water pump pulls cooled water through the thermostat into the engine.

          1. Haha, looks like I did draw you down the rabbit hole. But you’ve still got some things mixed up. Water from the engine block goes directly into the underside of the crossover pipe, sealed by two large O-rings. You can see match up the bolt holes on the block surrounding the water exits to the crossover pipe. The smaller metal end of the crossover pipe goes to the heater core, and the larger end goes to the radiator. The rubber hose goes to warm the idle air control and then throttle body. The thing on the top side of the crossover pipe picture isn’t a cut hose, it’s the coolant temperature sensor.

            On the water pump, the third port is the return from the turbocharger (top right). Oil cooler return is on the left and heater (and throttle body…) return on the lower right.

            1. What’d I get wrong about the crossover pipe? Everything you said about the crossover pipe is how I understood it, as well. (OH, I see a photo is missing and it says “hoses” instead of “holes.” I bet that was it.).

              Also, isn’t the tank in series with the turbo?

              Anyway, once I looked it over, I realized it’s a fairly straightforward cooling system, but definitely different.

    1. Back to the “we haven’t gotten there yet” haha I appreciate the advice. I wrote exists where I should have put enters at a previous response above haha.

      Jim from Cableshift.com makes these cable conversions. This is his first 6speed subaru piece… so we have to make the adapter brackets. Check out his site… its pretty simple and rad

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