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Old 01-25-2007, 10:21 PM   #4
NASIOC Manufacturer
Member#: 74110
Join Date: Nov 2004
Location: PERRIN Performance


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.

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.

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!

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.

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.


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.

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.

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.

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.
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Last edited by PERRINJeff; 11-01-2013 at 07:34 PM.
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