View Single Post
Old 01-25-2007, 10:19 PM   #1
NASIOC Manufacturer
Member#: 74110
Join Date: Nov 2004
Location: PERRIN Performance
Default Perrin H6 Build up - Complete Results!


( This is also available on our website at

This is kind of long, so sorry ahead of time. You can just skip to the bottom see the dyno graphs, but that would be no fun.

Summer of 2005, SEMA was coming up soon, and what could we do that would wow people. With ideas floating around about different cars to buy, build, or mod, we were kind of up in the air about what to do. Then the word H6 came up.



There are many things about this engine that are very cool. Just looking at the specs doesn't do it justice. 3.0L, 6 cylinders, DOHC, AVCS, AVLS, 250HP in stock form, aluminum block, forged steel crank, chain driven cams, and only .700" longer than an EJ20! Did I mention 3 point zero liters! Being familiar with the 4 bangers, the first thing that I was interested in seeing was how the Variable lift worked. The cams are the first strange thing you see as each valve has 3 lobes. One central lobe for the low lift and 2 outer ones for high lift, longer duration. The bucket is where the magic happens. There is an inner and outer piston that rubs on both cam lobes all time. When the solenoid allows oil pressure to shoot through the oil gallery, it locks the inner piston to the outer piston/bucket, and bam, new cam profile. I have to say this is probably the coolest part of the engine. Word is this is a co-developed technology from Porsche and Subaru, sure enough the parts are made in Germany.

Cutaway of EZ30R, aka H6

After getting the engine in hand a few other things that surprised us. The manifold is plastic, which sounds scary. But like other intake manifolds on cars, this is a glass-filled Nylon, which is good to 400+degrees and will hold high pressures at these temps. Plus the way these are manufactured, they allow for very smooth, very large internal diameters. Second surprise is the ports on the head. They are huge compared to the 4 cylinder ports. I was a little worried as since each runner is feeding smaller pistons they might be smaller than the 4 cylinder ports which feed larger pistons. But we were wrong. Another thing that we really liked was the throttle body. Yes its feeding a bigger engine, but it is feeding less power, so smaller throttle body??? Nope! Even better it was bigger! 3"OD vs. the WRX 2.75". Another good surprise.

Of course everyones worry once the heads came off, was the cylinder walls. They were a little smaller than the 2.5L walls and so were the iron sleeves cast into them. But would this matter was the question. As far as cost and time goes, re-sleeving wasn't really an option for this first build.

This build was a test of the basics of the H6, so drop in pistons were the answer we were looking for. With recent interest in Supertech products, we sent them an OEM piston set to build our first set of custom pistons. Because this was a SEMA car, Willy at Supertech was very excited about doing the H6 build as it was nothing he had seen before. This was a huge help in getting our pistons right away and getting the ball rolling with the build.


As mentioned above, the first build was done to test the waters. There was no need to sleeve or do other crazy things if the head bolts don't hold, or the chain fails, the oil pump doesn't pump enough, or who knows. Forged low compression pistons were a great answer to proving the H6 or not. Now that the Supertech pistons were being forged and machined, we could continue with planning the other things to complete the build.

Interest in the build was also seen by a few other close friends at PDX tuning, and another from a place where they talk funny, Minnesota. Because these friends and myself were 100% on board with the build, we had Supertech build a couple more sets. Everyone had their own idea with how they were going to build their motor, talk of sleeving, porting, valves, an monster turbos were making us rethink the decision of just pistons. But we needed to stay focused to ensure we got done before SEMA. With the engines apart and ready for some new pistons, the builds began.

Because there wasn't any aftermarket parts for this engine we turned to Subaru for many things. Factory head gaskets, piston rings, head studs and other gaskets were used to reassemble the engine. The cases were not split, so factory rods remained in place, as did bearings, and we trusted the OEM clearances were good to go.

Time to drop the pistons in! Just like they should, they had the right clearance we speced out, and they fit great. During the installation, we came across another thing that differs from the 4 cylinder. The wrist pin installation is just a little trickier. In order to get to that center cylinder and its wrist pin took some patience, and custom tool. But once we got the hang of it, no big deal. The wrist pins fit the pistons and rods perfect, so it was time for the next step.

Of course in building an engine like this, there are many new things that come up. Because of our experience with the 4cylinders, there isn't really any need to reference the manual except to double check the head torque sequence and a quick glance here and there. But with the H6 forget it, you need the manual nearly the whole way. There are about 100 times more bolts and more important torque sequences to deal with.

The first one is the head. The sequence is not what you think it would be (inside out) and the torque applied to the bolts was much less than the 4 cylinders. But like we said before, we would keeping this simple and doing one test at a time. So follow the manual it was.

An obvious difference in the H6 compared to the 4 cylinder is the front cover, and what lies behind it. Subaru designed this engine to be as short as possible, and to do that they used chains to drive the cams instead of belts. It's a little scary at first, but thank goodness for the manual. But after all said and done, it's just like the 4 cylinder where marks point in certain directions, and marks on the chain and gears make it very simple to install. Then the front cover goes on with about 100 bolts. The other difference is there is no real oil pan per say. The pan, is a major structural part of the engine, which has the studs for the tranny, adds rigidity to the two halves of the block, has oil and coolant passages and contains the baffles for the oil.

So in the end everything was set, pistons fit perfect, had the right clearances, (thank god for Supertech doing their job) there was not a single thing that went wrong with the build, that we knew of...................


What would .5 extra liters of displacement get us? Better spool? More power? These questions all lead to one thing, the TURBO! This was an easy choice. We would use the most commonly seen GTXXXXR name thrown around the boards, the GT3582R. All people considering a rotated turbo always fight the decision between the GT3076R or the GT3582R. The downfall to the GT3582R is lag, and what helps with getting rid of lag? More displacement! This would the turbo to use, and show off what a 3.0L can do. Plus this turbo I already had sitting on the bench, and it would flow enough air to make 500 WHP easily.

To bolt this turbo to the engine, we would use an off the shelf PERRIN kit. In order to make an off the shelf PERRIN rotated kit fit, it would all come down to the header. To start, we made a fixture to locate where the OEM uppipe inlet flange resided on a 4 cylinder. Transferred this fixture to the 6 cylinder, and we had our starting and ending points.

So what kind of header, equal length, how long, where should they collect? Again sticking with a keep it simple but functional attitude, we made the header like the OEM header. From the head, the 3 exhaust ports collected about 8" down the tube. From here a properly sized tube was chosen to join one side of the engine to the other. Then each side collected and mated to the uppipe flange fixture we made. The header was perfectly functional, but it had definite room for improvement, but we would have more time after SEMA was over. Header done, check!

Overall shot of version 1.0 header. Very simple but functional header, that proved its worth.

Passenger side of header showing quick, short collector, and OEM uppipe connection.

Drivers side header. The use of Tial V-band flanges worked great and we would definitely be using these for the future header.


Another thing that had to be designed was the engine wire harness. Most people would just run away screaming like a girl but this when the fun started! There nothing like taking a 2 month old 06 STI and cutting factory wires! The 2.5L engine harness was used as a starting point. Both the H6 harness and the STI harness were torn apart and laid out over the engine. Then began the cutting and splicing, soldering, and stripping of the electrical tape. I wanted to make sure the engine was as OEM looking as possible that meant using the OEM plugs as much as possible. After the harness was laid out and all soldered up, a fresh layer of electrical tape and wire loom was wrapped all over it. Looks like it came from the factory that way! That is what I like!

The chassis electrical system was simple. It was simple for a couple of reasons. One, there was 2 more cylinders, so 4 extra wires, and coils and injectors were taken care of. Then a couple wires for the lift solenoids, and we are good to go. But what would plug into the factory harness, and run the car?? That answer was easy. HYDRA! Andrew at Hydra EMS USA was ready and willing to write the special code needed for the different crank trigger and cam triggers. He was especially excited as there was a well known ECU manufacturer, that at the time, couldn't get an H6 running. So there was motivation there. The ECU was an off the shelf 05 STI unit with the plug and play harness, and a flying lead for the 6 new wires.
Electrical done!


Next is oil and coolant for the turbo. Where do we get these as there was no stock turbo on this engine. Oil was easy to get as the AVLS solenoid block was right next to the turbo. We will just tap into one of the plugs and get pressure there. Getting rid of the oil from the turbo was a simple dump tube draining into the oil pan. There were coolant passages all over the engine, it was just trying to figure out which one to barrow for the turbo coolant input and output. After some digging through the factory service manuals, to check coolant flow, we had our lines to tap into. Some tees, and unions, and turbo had it vitals and it was ready for firing.


The fueling was something we were a little worried about, as the stock H6 injectors were way too small, and they were not easily modifiable. But luckily some good-ole blue WRX injectors fit perfectly. And they are easily moded. The modded WRX injectors flowed roughly 800cc's and they would be good for 750-800 engine HP on pump fuel. Next is the fuel pump. The obvious easy choice is the Walbro 255LPH pump. It would support 500WHP easily, and it is a tried and true fuel pump. This defiantly wouldn't work for going too far beyond 500,but it would be the perfect answer for this time around.

Like all other Subaru fuel rails/systems, the H6 rails, were not going to cut it. First off the rails are NOT a traditional returning type of fuel rail. The rail is also NOT a return less system, its something in between. There is no "fuel flowing" through the rails. The regulator is located right where the feed enters the rails, so the fuel never flows through the rails and out the end. I experimented with this partial return less system on an FP Red and it worked. But for this build, the less experimenting the better.

Like the other PERRIN high flow rails, these were going to be setup equal length. Plumbing in some large .375"ID hose to the end of the rails would easily supply enough fuel. The stock STI fuel pressure regulator would be used as there was no need to raise the pressure beyond the factory 43.5psi, and we were not using a 1000HP fuel pump this time around.

Fuel rails shown with PERRIN Pyroshield installed over fuel hose. The OEM rails were used as their ID was plenty large enough.
* Registered users of the site do not see these ads.

Last edited by PERRINJeff; 11-01-2013 at 07:25 PM.
PERRINJeff is offline   Reply With Quote