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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. build_h6sti_h6cutaway 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 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, and 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, its 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.  Oh and it is an oil pan also. 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! build_h6sti_oldh6headerdp
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 definatley 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 moded 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.   build_h6sti_fuelrail
Fuel rails shown with PERRIN Pyroshield installed over fuel hose. The OEM rails were used as their ID was plenty large enough.


This was the simplest choice we made, the answer EXEDY Twin plate.  The only item that we didn't have to worry about working for this build was the clutch. The twin plate can hold 600ft-lbs of torque while feeling nearly as smooth as a stock clutch. Not much more to say about that!


The engine was all assembled and ready to be dropped in. Like dropping in the 4 cylinders, they either slide perfectly onto the tranny, or you fight to get it just right for half an hour.  The engine just flew onto the tranny like it should, and like we hope it all cleared everything. Well kind of.  The super soft OEM engine mounts sag quite a bit more than the stock STI mounts. So much so the uppipe hit the sub frame a little. Out comes the plasma cutter, and we now have clearance.  Next up was the cooling system.


Again keeping its simple, we used an 05 H6 radiator. The H6 engine has coolant inputs on each head, and in turn the radiator needs 2 outputs.  The OEM radiator was the ticket. It's the same as the STI radiator in thickness so it would at least support 400WHP with the cool weather we have in Oregon.  An interesting find was the stock H6 Thermostat was very hot compared to the STI. We decided to leave it in and see what happens. The amount of coolant the engine takes is basically the same as the STI, so nothing strange there. But there is one fluid that makes it very different than a 4 cylinder.  Luckily I bought a case of oil, because the normal 4 quarts turned in to 7! Yes seven quarts! Now the oil changes are going to $55. Just a small price to pay for big power.


Now that the engine is in, time to connect the turbo to the intercooler, and then to the throttle body. Nothing special about this, just started with an off the shelf WRX FMIC kit and added some bends and couplers, and we are done. The throttle body is much closer to the firewall than the STI is, so some modification to the last boost tube was needed.  BOV was placed between the fender well and the throttle body on the boost tube, and it was now time to fire. build_h6sti_h6_35r_engine_2_small
PICTURE OF Engine with 3582R. It looks like it is supposed to be there!


With a base fuel map from my good friend Jason, and quick calculation of fueling needed base on the difference of the H6 and STI, it was ready to fire. First some oil priming to ensure there was at least some oil on all the bearings. First click of the key, and BAM!!!  It fired right up! But there was one thing that made me instantly turn the engine off.  A very scary rattle/no bearings/no oil/something wasn't installed right sound. Fired it again and this time gave it a few seconds, still the noise was there. What could be wrong?? My stomach sank. One more try, this time I would get out and listen.  Fired right up, and just as I was about to get out, I lifted my foot of the clutch and the noise went away. WOW, that was a good feeling. It was just the twin plate Exedy.  Exedy told us that extra noise is normal with these clutches, but WOW, they are noisy! Now that the scary sounds are gone, the car was allowed to run for an hour, and go through the heating and cooling process a few times. The first thing everyone noted was sound.  That was such a sweet sound, and I was looking forward to reving this baby up. Time to take her home!  Being the trusting person I am, what could go wrong?   Well nothing did, and we had 2 weeks before we left for SEMA. I was definitely going to take it easy for the next couple of weeks.


As with all my past personal cars, water injection was a must. I started looking at the 2D system for my car, which of course is one of the most versatile systems Aquamist makes.  This system is would do everything I need it to do and more. Since we were working on building our SEMA car, a quick email was sent off to Richard, who is a genius BTW, and in no time, a response.  I told Richard what we were doing for SEMA and he was very excited to be part of our car and offered up something special. But he wouldn't tell me much about this special system. As time passed I started poking at him about building system that would be special to PERRIN with some features I thought were important. With my constant nagging of a dream WI system, I didn't want to push to hard for a date when the special SEMA WI system would ship. I was getting a little worried. It was now 1 week before SEMA and a box from a far away land showed up. Holy SHIT! I think were my exact words. I couldn't believe what Richard had done. I was expecting a pump some nozzles, injectors, bunch of wires, basically a 2D system with a couple extra things thrown in.  Boy was I wrong. This was the craziest, most thought out WI system I have ever seen. Special Nozzle holders, nozzles, pressure check valves, Twin pumps, mounted to a board with nozzles, relays circuit boards, dash display, and all incase in a plexiglass case!  Richard went above and beyond for us for SEMA. build_h6sti_h6_side_shot_small
Aquamist port injection nozzles installed. These are special .3mm nozzles with individual nozzle holders.
Close up shot of nozzles and holders. Love these holders!  Wish they included them with their other systems! Hmmmm......
The FIA2 is the injector amplifier used to drive the signal for the Aquamist injector.  (2) Purple solenoids are used to turn on and off flow to the nozzles. One solenoid controls the port injection nozzles, and the other controls the pre-turbo nozzle.
This is where the magic happens!  Twin pumps means 2 times the flow.  Another FIA2 is used to amplify the signal from teh front to the back. You can see the relays, fuse panel, and the injector all nicely mounted on the board.  What you don't see is the accumulator located between the pumps.  Richard sure spent alot of time on this!
Again, Richard went nuts creating this system for us!  Switch number one is to arm the system, switch number 2 is for checking the level switch.  Port injection on/off, and pre-turbo injection on/off are the last two switches.  The other things you can't see is the wire harnesses, that connect this all together.  Hmmm...... Dash display......plug and play harness........nozzle holders.........  pump and electronics all mounted on a injection.........i got an idea what to do with this!
This relationship would not only pay off for SEMA, but for something else in the near future.

SEMA 2005

Day one of SEMA 2005, the PERRIN H6 STI debuted.  After months of work, and a 2000 mile drive from Portland to LV and back, the car had made it. The payoff was well worth it. It was our first year attending SEMA as a company, and the car was a hit! build_h6sti_h6_35r_engine_small
Almost too factory.  Many people just walked by thinking just another STI.  Toward the end of the show, we ended up putting a sign, 'Turbochaged H6".  But anyone that new what a Subaru engine looked like, knew that something didn't look quite right.
Picture of our booth at SEMA.  This was our first year at SEMA, and it turned out great!
  All of this wouldn't of happened if it weren't for my sponsors, and support from my friends and family (not appearing in any order) Special thanks to Dustin Harris, Jeff Sponaugle, Jarrad Bowen, Adam Taft, John Herring, Ben Collins, Adam Koppel, Jason Bluth, Richard of course from Aquamist, Willy Tagliavani from Supertech, Roland at H&R, Andrew Nam from Hydra EMS, John Lietl from PIAA, Toyo, Autopower, the crew at  PDXTuning, and of course my wife for "allowing me" to work on my car more than be at home...... And that concludes the story. Oh wait, the story is just getting going.....    


After the 2000 miles, and a week of standing on our feet, and not sleeping much, we arrived back home.  We took a step back and looked at what we had done.  It was a crazy time leading up to SEMA, and now it was time to take a breath and relax. Ya, for about 1 minute! The next day, the tuning had begun!


One of the most important parts of the build is the tuning. As with any high performance engine anytime you ask more than 2 times the stock power, tuning becomes very important.  With the 4 cylinders, and the experience we have, things like timing curves, fueling needed, and Air Fuel Ratio the engine likes to see, are almost a no brainer.  Who knows what we would find. Starting with a low 10psi boost setting, and a safe 10.5-1 AFR, the tuning had begun.  After weeks of road tuning, we started to see what AFR it liked to run, and timing it needed.  Like the STI, 10.5-1AFR was way to rich and it seemed to be happier in the 11.5-1 area.  From there it was time to play with the AVLS system.  When to turn it on was the question.  From Hydra it was set to 5500 RPM. This sounded like a good starting point. The more miles were put on the car, the higher the "redline" became.  Until this point the tuning was going fine, and the redline had slowly increased to 5500rpm. Then the day came when I decided to bump the redline to 6000.  Up until this point the car was fast, but not 400WHP by any means. The first pull and at 5500 the car came to life! It was a little scary, kind of like a huge turbo with big lag.  What changed at 5500RPM?  Oh ya, that is where the lift turned on. Because of this huge onset of power, I started turning the lift on sooner to see what happens.  The lift was slowly turned down 500 RPM at a time until it felt like it wasn't getting any faster.  An interesting thing is turning the lift on lower than 3500RPM would actually make the BOV blow off!  This was happening because of the instant onset of the different cam profile, would cause a huge drop in manifold pressure, in turn the pressure in the boost tube was higher causing the BOV to blow off.  This wasn't going to work, so some where in the 3700-4500 range is where it felt best.  So how would we determine which is the best and most powerful RPM. From there we turn back to HYDRA and its auto fuel tune feature. This feature is a great way to get fueling close quick.  First was to set lift on point at 6000. Let the ECU do some tuning and save that map. The set the lift on all the time, and let it work some more magic. When comparing both maps created from the auto tuning, there was a very interest dip. With the lift set at 6000, the fuel map was adding fuel up until about 4000-ish RPM, then took a huge dive until the lift came back one. In similar but opposite fashion, with the lift set on all the time, it would remove fuel up until about 4000-ish RPM, then start adding beyond that point.  From comparing both maps, it became pretty obvious 4000RPM would be the magic lift point. At least for the GT3582R turbo, and header setup. build_h6sti_hydra_screen
Just a quick shot of the Hydra interface software. It simple, and very easy to figure out. But MAN they need to get rid of that ORANGE back ground! Love that auto tune feature to get your base map going quick.


Now it was time to start turning up the boost!  Slowly but surely the boost climbed from 8psi to 16psi. Obviously 16psi felt way faster than 8psi.  But the question was to go beyond this point?? Because the engine this go around was all a big test, we didn't know how much power this thing could take, so 16psi it was!


Finally the day came when it was time to dyno the car.  We heard of this place close by, PDXTuning, thought we might try their dyno out J Yes that was a subtle joke.  First pull on the dyno and 420WHP! Now we are talking! With about 20 pulls at 14psi, and further fuel and timing tuning, we bumped the boost to 16psi. 438WHP and we were good to go. This WHP was a commonly seen WHP amongst many STI owners, so this was nothing too special.  It might have been special when we broke 400WHP on our 04 STI back in 2003, but not now a days.  An interesting thing to think about is the HP per cylinder this engine has compared to the 4 cylinder engines.  The rather normal 400WHP seen by many STI owners is becoming a somewhat safe WHP level for the stock STI engine. With 6 cylinders, and 440 WHP, that is only 73WHP per cylinder. That is almost 300WHP on an STI. Which is very safe, and this is with non forged pistons.  With forged pistons in the H6, we were feeling good about this power, it was time to go beat the car up some more. dyno_h6stih6original
Picture of  440WHP run with just the drop in pistons.   The rather normal 400WHP seen by many STI owners is becoming a somewhat safe WHP level for the stock STI engine. With 6 cylinders, and 440 WHP, that is only 73WHP per cylinder. That is almost 300WHP on an STI. Which is very very safe and this is with non forged pistons.  This is just showing that the engine isn't under much stress to get this power.
  The thing I grew to love (besides the sound) was how much low end power the car has. To give you an idea, 16psi would be had by 3100RPM, and this is with a GT3582R. The car is unbelievable to drive.  Stock STI turbo spool with GT3076R power, what more could you ask for.  Again because of the unknowns with this engine, we decided to leave the boost at 15-16psi, and see how it goes. Because I have a small "race track" on the way to work, there were many many 4th and 5th gear pulls done to redline, and I was amazed the car was running perfect!  Day after day, pull after pull and more than 400WHP. As months passed, an interesting thing started happening, burning oil. This only happened under long decels, the eventually under idle conditions.  First thought was this was a crank case vent issue. The engine only had 2 ports and they were on the driver side. Time to start messing with adding more, and better placed vents.  Starting with adding 2 more vents to the drivers side valve cover.  Eventually a crank case vent/oil fill cap vent would be added.  At this point the engine was freely breathing, but still the oil problem. It was pretty minor, as the consumption was about 1 qt a month. Before we gave up, maybe the turbo was getting too much oil??  So we installed another restrictor, and nothing different, still oil consumption under no load. Maybe the turbo would get too much oil at low RPM and not enough at high RPM.  So we did a test to see how much oil was coming out with at idle.  Hmmm, no oil???   So I reved it up and right around 4000, out came the oil.  Hmmm, that means the car had almost 3000miles of driving with virtually no oil getting to the turbo!  After finding a new CONSTANT oil supply for the turbo, I was worried about the turbo now being bad.  It was perfectly fine, which goes to show Garrett turbos don't need much oil to function. Not enough oil drainage was next. So a better straight shot from the turbo to the valve cover was the ticket.  But same thing still burning oil.  But the car was still amazingly fast, and the compression was perfect. So not too much to worry about, and it was time to take the engine to the next level.

SEMA 2006

With all the talk of Time Attacks, Drag racing, and other plans of racing, we thought lets build this H6!  Lets make 1000HP!  Let's blow the minds of the SUBY community again. We needed a goal, and a reasonable goal was 1000 engine HP, which would be somewhere around 750-800 wheel HP. And of course do this on pump fuel (ok that might be stretching it).  What would we need to do this?  The list started. GT4294 or GT4088R, Sleeves, rods, valve springs, Ti retainers, head work, new header, and even a larger IC was discussed. A couple of things had to remain; this car still had to be drivable, and had to run on pump fuel.  Also boost response was important, as was low end power, there was no way I was going to sacrifice this.  So we would start with the Gt4088R.  It can flow enough air for 700 engine HP and get us close to where we need to be.  But with this turbo, the only way to break into the 750 area, would be with nitrous.  If this turbo turned out to not flow quite enough, we could always replace it with the bigger GT4294R. But, one step at a time.


So the second time around, we created a list of what needed to be done.  Sleeves, rods, valve springs head studs and retainers were the biggest part of the list.  Using some contacts from PDXTuning, the sleeves were on the way.  A set of rods and OEM dimensions were sent to Pauter to get the rods going. The valve springs were just like everything else, they had to be made.  Off went a head with cams and valves to Supertech. Saying all that in a couple of sentences makes it sound easy, that just wasn't the case.  As with all special projects, the delivery dates started with one date, then changed, and then changed again, and finally when the parts were about to show up, they got delayed again. After a couple of months, parts started showing up.  Time to pull the H6, and start removing parts. I was kind of hoping to find out what was causing the burning oil. From constant checking of spark plugs and compression tests, we knew it was something with cylinder #1.  With the heads off, everything seemed to be fine with valve stem seals, but there was some oil in the combustion chamber.  So next was the piston.  As the piston in question slid out, it was kind of like 2001 a space odessy.  In slow motion, the top of the piston is seen........ then the first compression ring popped out..........then the second here comes the oil scrapper ring....wavy ring, and..........hmmm.  Nothing.  Ah, that would be the problem!  Man that was a relief.  In case you didn't know, you need ALL the piston rings in order for the engine to function properly. I will have to remember that one J.  Yes, it was an oops, and a big one, but hey, oops happens.


Of all the things done to the H6 block, this was the one item that many of us argued about actually needing.  The funny thing with sleeves is they are not that expensive to buy.  But installation is a different story. The single largest cost involved with building the H6 engine is one of the cheapest parts.  This duty was left up to a local engine builder. As was balancing of the rotating parts and assembly of the bottom end.  For an extra $400 we got a warranty, and a professional engine builder to build the block.  Sounds good to me, so I thought. build_h6sti_sleeves2
This was one of the nicest looking part of the build. Freshly machined iron, and brand new Supertech pistons, are amazing looking.  They won't look like this ever again!


When the stock rods were pulled out of the block to be sent off to Pauter, something a little scary was discovered.  Putting the STI rod, the WRX rod, and the H6 rod next to one another, made it look like those little chickens that fit in side of one another.  The H6 rod was a joke compared to the other rods. It was thinner in all directions, and it was much lighter. In this case lighter wasn't better. Like other Pauter products, the custom H6 rods were amazing. The finish was amazing, and they came with ARP bolts, like all good rods. Too bad no one would see them!
Above pics show the difference in the Pauter H6 rod, vs. the OEM STI rod, and the H6 rod.  Its pretty visably different.   Besides the side profile shown here, turn them 90 degrees and you will see another huge difference.  They are much thinner in all directions.
Shows the side profile of the rods installed in the block.  You can see the oil gallery plugs. Behind them are huge ports feeding each of the rods, and main bearings.  Also visable is the lack of the pan. This large surface is where the lower block/pan bolts to.


Supertech was amazingly fast with getting us valve springs and ti retainers. This was a very critical part for the build as the OEM springs were a joke. The rates are so low that the Supertech springs for the exhaust side were almost 3 times higher rate!  Needless to say, after installation of the springs, the heads would be good to rev to 8000 and maybe 8500. But at this point,  who knows if this is even necessary.  We will soon find out.  Now what to hold the heads to the block?  That's easy, ARP. build_h6sti_head_retainers
Again, more parts we hope to never see again! Installing springs on the heads were very simple on the exhaust side. But the intake side with the variable valve lift, forget it!  the added depth to each buckets bore, made it a 2 man job!


As with any Subaru 4 cylinder build, stock head studs don't cut it when you are doubling or tripling the power. The stock H6 head bolts are similar to the STI in that they are a bolt.  That is where the similarities stop!  The biggest difference is the bolt is an socket head bolt not a 12point hex bolt. The problem is that the head of the bolt didn't have much material to support the added torque, and with the stress this engine would see, they were not going to cut it.  Also they were 1mm smaller diameter than an STI head bolt.  So we turned to ARP. The only choice as far as I am concerned.  Custom length and diameter studs from them took way too long, and this engine build was starting to wrap up.  So another solution was needed.  With some quick measuring, we found modifying an STI head stud from ARP would work.  We just needed a spacer between the head and nut for the stud. Some simple 4130 steel spacers, and problem solved.  This time the build went much smoother.  We were still using the manual for torque specs and sequences, but the assembly felt more like the 4 cylinders. build_h6sti_sleeves1
An integral part to the build is is the head studs. There is no way we were going to use the OEM bolts to try to hold 800HP.
This time around it was time for a new paint job.  A couple of stencils for PERRIN, and PDX and it looked great.  Hope this never has to come apart again!


After the engine was all back together, it was time to figure out where the GT4088R would fit. Since this turbo is a twin entry (or Twin Scroll) turbo, it might be a good time to do a complete redesign of the header. In similar design to the first header, the 3 ports would collect about 8" from the head. From this point is where it changed. Each side of the engine had its own collector and secondary tube. Each secondary tube would power its own scroll of the turbo.  So the header could be called a 6-2-turbo. Because of the firing order of the engine, this setup would provide nice equally spaced pulses for each of the turbo's scrolls. build_h6sti_newhdrdriver
It was a long process, but it was really fun building the header.  If you see a production H6 kit, expect the header to look just like this.
Very tight quarters, but packaged like it would from Subaru.  Well kind of.
There is more of those TIAL 44mm Flanges.  The subframe was cut in order for header to clear.  Because there is no real structural member after these points, it was not big deal.
  This was a very time consuming project, but in the end it paid off very well.  With the turbo mounted in the magic place, and the twin scroll header set up, we could build the downpipe and be done. The GT4088R uses a 3" V-band outlet which is such a nice clean setup, until you have to use them and remove them.  As nice as these are, they are a pain in the ass to deal with as you have to get them lined up just right before you tighten the clamp. But who cares, it wasn't like I was going to pulling the DP off all time, right?? And not to leave out the Wastegate.  Just like our other Rotated Turbo kits, we used a Tial 44mm gate. Since the header was a twin scroll header, we didn't want to destroy the equal pulses entering the turbo.  Normally people would just stick (2) wastegates on each scroll and call it good. Since nothing else on this engine is normal, we would make a special single wastegate work.  With some carefully welded tubes, and dividers, we created a perfect single wastegate for a twin scroll setup.


One of the things we discovered with the first build is the engine runs pretty hot.  An oil cooler was added this time around to ensure the oil stayed nice and cool, and maybe help keep coolant temps in control.  Of course this adds even more oil to each fill, and makes the oil changes about the same a big diesel truck!  Like we said, the engine runs hot, hotter than the 4 cylinders by about 5-10C.  So next up is a radiator.  A Koyo radiator was purchased, and modified with 2 entry points for the H6 engine.  We also added the STI thermostat, which is 5degrees C cooler. All this should help control temps for any situation. build_h6sti_710cooler
WRX fog light used for a vent for the oil cooler.
In making room for the header, we had to find a new place for the filter, and OEM oil cooler/warmer.   Why not use a WRX fog light cover and put the heat exchanger behind it.
Another shot of the packaging.  We kept the header as close to the engine as we thought was exceptable. This was important as we didn't want to be boucing the header off speed bumps, and boulders.


So a little more oil, and a little more coolant than the last build, and she is ready fire!  Just like the time before, it fired right up.  Went through a few heat cycles, and now some quick drives.  Not knowing what kind of oil supply this turbo needed, we discovered an extra restrictor beyond the one was needed. In fact so was a second, so three total.  We definitely weren't worried about the turbo not getting enough oil J.  So, now it was just a matter of time to break the engine in. No plans for another LV trip so it would be a few weeks before it was ready. First impressions, was it was laggy.  Before, we would get full boost by 3100 RPM, and now it seemed much worse. But I wouldn't judge this until the engine was all nice and broken in. So low 8psi of boost was ran, and slowly but surely the RPMS were raised up.


Then the day came that 500 miles were on the odometer. So I decided to do a pull to 7000RPM. First a 6000, then 6500. But I noticed a strange sound. My stomach started hurting, as this sound was rod knock type sound. This was bad!  Babying the car back to work the next day, the sound got worse and valve train noise starting happening.  This is not good.  The engine came out, and was disassembled.  Sure enough, rod bearing #2 has a little more clearance than the rest.  Say about 50 times more clearance!   Thank goodness we paid the engine builder to assemble it, because it would have a warranty, right??  WRONG!! The builder of course blamed it on oil supply, or improper break-in, not enough oil pressure, too much boost,  or knock, but nothing that they did of course.  Being a reasonable person, I looked into his suggestions.  Boost didn't cause it, knock didn't cause it (have logs), so I looked to oil.  Plenty of oil was in the engine and not a bit was ever consumed.  Oil pressure, ya right this thing runs 100+psi, and that wasn't' the problem. The argument back was that was way too high, and the added friction from the added pressure could have broken down the oil (due to heat), and caused this.  I don't buy this at all, as all JDM STI's have shims to add oil pressure. It basically came down to there were too many things that could have caused it, none of which could be proven it was their fault or mine.


Now that SEMA is approaching quickly, plans started changing.  With the H6 broken, the Legacy Spec B and STI Limited coming out, we thought for SEMA we would show off a different side of PERRIN. Something that better represents what we really do. Plus the H6 was there last year, so its old news!  The H6 is a great show piece, but it's not like we are building these all day long and selling them. So the focus on the H6 project was turned to a brand new Spec-B Legacy, and Limited STI sitting at the shop.  In great contrast to the H6 build, these would be much simpler and much less stressful builds.  This sounded good with SEMA quickly approaching.  We built the cars to show off what any customer could build using our catalog.  They were great hit at SEMA, and it was nice not having to throw together the H6 at the last minute.


Now that we were back at home, H6 was on my mind, and Subiefest was quickly approaching.  At this point I am not happy with the bearing failure. I thought I did everything by the book.  Starting with the basics of the engine I started checking into things like oil pressure, and oil pump flow.  These were important things to figure out for the third time around as we didn't want another failure.  I figured I would talk to the builder about the rod bearings and the clearances they had before assembly. Thinking maybe the failed one was tight or loose.  Then I find out that the builder couldn't tell me any of the clearances of the bearings!  Didn't write them down!! WHAT!!! Still not happy, and now doubting the engine builder, the engine, and many other things surrounding how well this will hold up.  Well another $2000 and it runs again. Long story short, everything went back together just fine, but this time we are going to 1000 miles for the break in at low boost and RPM. I would like to pretend this didn't happen, and it was all a bad dream. build_h6sti_jeff_building
Last time i would be assembling the H6 in 2006.  The paint held up ok the 2nd time around. If there was a 3rd time around, i would be throwing this thing through the window of the machine shop.


I would like to pretend this didn't happen, and it was all a bad dream. Subiefest 2006 was the maiden voyage of the freshly re-built, re-honed, re-balance, re-ringed, re-bearinged engine, and it went perfect!  It was also the first time the public had seen the new engine, and turbo combo. Besides the few people that walked by casually thinking it was just another STI engine, the car/new engine was a hit! Plus we got to put tons of miles on the engine and lots of great road tuning. 1500 miles and time to put in synthetic oil and take this baby to the dyno!


First pull on the dyno wasn't as good as the first pull done months prior, but we were running less boost. None the less, it made decent power, and at the starting point of 14psi there was tons more on tap!  With further tuning at 16psi we realized there was major gains to be had. At this point in the tuning, most of the time was spent getting the fueling close. The timing curves we had from the previous tune was pretty good, and we didn't want to push the limits too far.  As we found, this engine would make more power with boost, not timing.  The goal with this tuning session is see what kind of "easy" power we have on tap.  We were not going to be pushing this engine this time around.  Also this is on pump fuel, with water injection using a 50/50 mixture.  All runs below are named by the boost seen at peak power. Example: The 16psi run is running 16psi at 6500, and a little more at 4000.


Above graph is 16psi with some fuel and timing tuning. By the change in this graph you would think the engine was running near misfire, but this was running 10.5-1 vs 11.5-1, with a couple degrees in timing change. We were trying to hit 500, but it just wasn't going happen.  Time to turn the boost up some more!
Above graph is 18psi.  Again that is 18psi at 6500RPM. The large dip in the graph was from the engine running a bit rich on initial spool.  Like seen at 14psi, fueling makes a big difference, this dip was .7AFR change.  4psi and we gain 80WHP and 80ft-lbs of torque, this is starting to look good!
Here is the boost curve of theGT4088R on the H6. The only change in the hydra between runs was a simple change in the boost target map. As far as changing boost, the HYDRA is very simple to do. The only thing we battled with is a falling boost curve. The spike at lower RPMs really helps with torque, but if we could only hold it!!
Yes it was called 22psi, but at peak power, it was 21psi.  Again 4psi and some great gains!  But we are starting to see the gains not so exponential, compared to lower boost levels. This is a sure sign of turbo starting to run out of air flow.  More on this later.  During the last few runs we started to see the boost curve spiking a little more, but it would still hit the target, 22psi.
Now the 2psi of boost change only netted about 20HP.  During the last few runs we started to see running a little lean close to redline.  First small amounts of fuel were added, then larger and larger with no changes to AFR.  We were SO close!  Well that Walbro was good while it lasted!  As we once thought before, the fuel pump wouldn't be enough for to much more than the 500WHP, but it at least allowed us to hit 600!
Well there you go 600WHP!  It was limited by fueling, but even if we had fueling dialed, I don't think there was too much more power to be had. Running more boost means more air flow, more air flow means we are going to be way off the compressor map.  Going off the compressor maps means turbo efficiency goes down the crapper, and in turn less potential power.
Here is the boost curve of the 600WHP run and the 22psi run.  Couple things here to take note of:  The actual boost needed at peak power to hit 600 WHP was just over 23psi! In contrast a 30R on an STI barely breaks 400WHP at that boost.


Air flow = HP and boost pressure = more air flow.  How ever you want to look at it, this turbo isn't big enough to flow too much more air or make too much more HP.  Below are some lbs/min ratings of the 3.0L at difference boosts and RPMs. So at 7000RPM and 16psi of boost flows 58lbs/min of air.  According to how Garrett rates their turbos HP, that is about 580 engine HP. Since we made 470Wheel HP, and if we use a 25% drive train loss, we get 580HP.  Sounds about right.  At 23psi and 7000RPM, the engine is flowing 73lbs/min, which is about 730 engine HP.  With drive train loss, that puts our 600 Wheel HP at about 750.  Again pretty close. build_h6sti_4088rcompmap
COMPRESSOR MAP OF GT4088R.  You can see using a basic air flow calculator that not too much more power would be had.  Esspecially on pump fuel.  But 600WHP on pump fuel, what more could you ask for.  Thought this wouldn't be possible without water injection.
  Since the turbo is only rated for 700 engine HP, according to Garrett, it is no surprise that we started to see diminishing returns as we got closer to 23psi. The word diminishing is not the best word to use as we were still making huge power. You can see by the compressor map that we were getting into the areas where the turbo was less and less efficient. Again showing why at high boost levels the gains were not as big as the boost went up. So was there tons more on tap?  Nope!  Can the H6 hold more power if there was??  I think so.   With the progression of power, and how easy it was to get there, and with power coming so easy with ZERO knock, there is sure good signs that it can.  Think of this build as WHP per cylinders.  600WHP on the H6 is 100WHP per cylinder.  100WHP per cylinder on a 4 cylinder is 400WHP, which many consider and have proven to be safe (with non-forged piston engine). To get 600WHP on a 4 Cylinder you will be at 150WHP per cylinder. That is 50% more stress, and pressure.  If we use the example of a forged piston, stock sleeved STI motor, holding almost 600WHP (150WHP per cylinder), the H6 would be good for at least 900WHP. That is pretty scary!  Add sleeves into this, and say 1200?? Thats only 50% more power per cylinder.  But that is all speculation, and stepping into dream land. So why didn't we go too much further? Fuel. As we got closer to 600WHP, we noticed that we were adding more fuel and nothing was happening.  A PERRIN chassis fuel system is the easy answer to fueling and making it 100% safe to run at 600WHP. As many have found, 550WHP is kind of the limit of the Walbro, and we just proved that stat isn't too far off.  As important as fuel is to this build, it is one of the simplest things to fix. This will allow, I believe, a safe 620-640WHP. But to go beyond that, it would be time for a bigger turbo.


Most likely nothing. At this point we have awesome power with 4000RPM of spool. Any bigger turbo and we will sacrifice spool and all the low end power we just gained with the bigger engine.  If we did go bigger, the next best choice is the GT4094R, but the extra 100 possible HP would only be for showing off.  At 500WHP, this car was pretty scary, add 100WP to that and it just became a dry weather only car!  In the state of tune it is in, it is far faster than most all other supercars at 1/2  to 1/8 the cost depending on if you compare it to a Z06, or a Ferrari.  This car isn't a trailer queen, or a dedicated drag car, or dedicated track car, or street car.  It may not be the best at those things, but it sure will do well at all of them. build_h6sti_fpr2
The one thing that will happen next is fuel.  We need more fuel to get more power.  The PERRIN fuel system and pump are installed and ready to do a retune at 600WHP!  Above is just one part of the system.  A fuel pressure regualtor.


Alright, now the fun stuff.  So how does this compare to your normal everyday STI's driving around out there?  From all the info above, you can probably conclude it has more power. This is true, but it is kind of fun to see exactly how much and where it dominates the 4 cylinder. build_h6sti_h607sti30r
The first comparo is our 07 STI limited. I think this is the best comparo as this is a very common setup. The 07 STI Limited uses a Full PERRIN package. Every single bolt on part we do is on this car. The rotated turbo we used is a GT3076R with a .82AR exhaust housing.  Running a modest 21psi boost level this setup can hit 400WHP pretty easy. And this graph shows it.  With similar spool to the Gt4088R on the H6, it does nothing but STOMP it everywhere!
The second comparo is highly tuned stage 2 STI. Again this is a good comparison as this is another common setup.  This car only has a slight edge below 4000RPM. But when you are racing, auto crossing, dragging, you will not be in this range very long, so again the H6 wins!  But on the road, below 4000, the Stage 2 STI will be much faster.
This comparo is a highly tuned GT3076R STI.  Again this is a good comparison as this shows a similar spooling and similar low end power car with the H6.  This GT3076R is really maxed out and on the 4 cylinder, a GT3582R will get close, but at the sacrifice of low end power.
The last comparo is a highly tuned GT3782 on an STI.  This turbo flows about the same amount of air as a GT3582R, but with a freer flowing turbine wheel.   Again this is a good comparison as this shows a 4 cylinder making about the same amount of power as the H6. But you can see what kind of sacrifices you make to get there.  On the road, there is about 1000RPM different spool, and about 13psi more boost on the 4 cylinder.  With the H6 running about 23psi to get this power, adding 13psi to the 4 cylinder to get close to this power, you are going to start having issues with head gaskets sealing, bearing taking a beating and quite a bit more stress.


The question is would I do this again?  One could argue that the power levels we reached could be done with a 4 cylinder.  One could argue that you would also save a ton of money doing the 4 cylinder. One could argue that the added weight will hurt handling. One could argue that it gets worse gas mileage.  One could argue that it is untested waters.  One could argue that 600 is way too much power for a street car. I say so What!   I think it is time to start a trend for a new Subaru Exhaust Note!   Bye bye Boxer-rumble, here comes the boxer-smoothie............or boxer-Porsche-aru, or boxer-Sub-orsche, or something that represents that it sounds like a Porsche.     build_h6sti_gt40rengine Questions, comments, feel free to email, or IM us at build_h6sti_gt4094r_comp_e

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