EZ36D H6-swapped 2006 Impreza 2.5i Build Thread

[LucasBlack]

Originally Posted by Patrick Olsen

Track event update ... go!

Haha! In short, it went well.

The car performed miraculously! It consumed no oil, coolant and oil temps stayed in check, and it just loved to run! My rev limiter was set to 6.8k rpm, and the car felt like it pulled strong all the way through!

Longer story was that Monday was the ONE day in the span of more than a week that did not forecast rain. And while it sprinkled a little in the morning and was overcast most of the day, the sun finally came out late in the afternoon AND before my last session!

Being out on the wet track for the entire morning in a car that all of a sudden has 80+ more horsepower (and that I haven't driven in 8 months) was a bit stressful, so the drying track and a little bit of sunlight was very welcome!

Checking Harry's Lap Timer and I was not as quick in a few corners as I used to be, but I still dropped 2 seconds off my best lap time. Time to grow some huevos with the new power and speed.

There was no photographer out on track (likely because of the weather), so I don't have any new eye candy to share. But there were a few interested parties who ended up taking photos of the engine bay. There were others still who took a look and only noticed the Odyssey battery and POM Juice coolant reservoir, haha!!


As for fuel economy, I netted 20mpg highway on the way to/from the track. Mind you, I was averaging somewhere in the ballpark of 4k rpm going about 78 mph because of my 4.44 FD gear; fuel economy isn't exactly my primary concern.
This may improve (a little) as we continue to refine and massage the tune, but I hope moreso that it eeks out a few more ponies instead.

Overall, a VERY successful weekend. My thanks go out again to the guys at Lifted, Inc. for all their work getting it ready!

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[LucasBlack]

Just realized I hadn't posted a 'final' engine bay photo (FAIL!), so here you go.

[Patrick Olsen]

Glad to hear the track event went well.

When I still had a 5MT in my car, I had stuck with the 4.11 gears but had swapped 5th gear from the stock 0.78 to the 0.87 that the Outbacks had (due to their taller tires). I was spinning ~4k at 80mph; I actually don't recall seeing much of a fuel mileage penalty. However, having a "useful" 5th gear definitely made a difference on the long straights at track events - I picked up 5-10mph on the front and back straights at VIR, for instance. Since my car shares DD duty (well, when it's not broken for over a year ), I figured I wouldn't want the H6 to be spinning those sorts of RPMs on the highway, hence the shift to a 6MT.

Other than your POM-wonderful bottle, it looks damn near OEM!

[LucasBlack]

OEM-like was definitely the desired end result; I prefer understated performance.

Yeah, with the 4.44 FD in there now, I do still feel that 5th gear is a bit of a dog out on track, though swapping it out would make for an even worse highway cruising RPM -- while not my DD, it still sees street time to get me to/from the track, some of which are 3.5 hours away.

A 6MT with an R180 would be nice; I consider it to be on my wishlist.

[ajracerfan]

What all did you have to do for the tranny? It really bolted right up? I've always been interested in doing this and it seems it's a little more of a possibility than I originally thought

[FuJi K]

I respect this!!!!

Originally Posted by LucasBlack

Installed a 4.44 FD from an auto-trans Forester; marks on LSD carrier are from when it was initially installed (by a different shop).

[Patrick Olsen]

Originally Posted by ajracerfan

What all did you have to do for the tranny? It really bolted right up? I've always been interested in doing this and it seems it's a little more of a possibility than I originally thought

If the same automatic trans will bolt up to either an EZ30/36 or an EJ25, and a manual trans will bolt up to an EJ25, then the manual trans will also bolt up to an EZ30/36. A 5MT or 6MT bolts up without issue - just have to remove the flexplate and install a flywheel and clutch.

[LucasBlack]

Originally Posted by FuJi K

I respect this!!!!

Thanks!

[LucasBlack]

Originally Posted by ajracerfan

What all did you have to do for the tranny? It really bolted right up? I've always been interested in doing this and it seems it's a little more of a possibility than I originally thought

As Pat has already stated, the mating of the engine/manual transmission is not complicated.

As for the swap overall, my main word of caution would be the electronics/ECU. Do your best to sort out your approach to this (considering the end goal/use for the car, desire to keep it street legal, etc.) before jumping in to this project. Otherwise, enjoy.

[ajracerfan]

Originally Posted by Patrick Olsen

If the same automatic trans will bolt up to either an EZ30/36 or an EJ25, and a manual trans will bolt up to an EJ25, then the manual trans will also bolt up to an EZ30/36. A 5MT or 6MT bolts up without issue - just have to remove the flexplate and install a flywheel and clutch.

Originally Posted by LucasBlack

As Pat has already stated, the mating of the engine/manual transmission is not complicated.

As for the swap overall, my main word of caution would be the electronics/ECU. Do your best to sort out your approach to this (considering the end goal/use for the car, desire to keep it street legal, etc.) before jumping in to this project. Otherwise, enjoy.

Excellent! Gotta keep my eyes open for a salvage or something then. I was just curious about the increased stress on the tranny due to the extra torque.

[LucasBlack]

Here's a shot of me getting close to being a little over-invested into Turn 5A at Thunderhill Raceway, haha!



Based on tuning and testing from a few days there, I'm looking to make some changes to my damping and spring rates. It has been fun relearning the car in its current state and finding out what all it can do again: the RWD proving to be more of a bear now that I actually have some power. I did finish Second in class for the SpeedSF Challenge time trial on Sunday, so that felt pretty good! My best time there now (for the 3-mile Bypass config.) is a 2:05.72.

And thanks to BillWangPhotos for a whole series of great shots on Sunday!

[ajracerfan]

Thunderhill!? The Thunderhill Raceway in Kyle, TX?

[LucasBlack]

Originally Posted by ajracerfan

Thunderhill!? The Thunderhill Raceway in Kyle, TX?

Thunderhill Raceway in Willows, CA.

[ajracerfan]

Damn I got really excited for a second. That's literally 6 minutes from where I live. Still, looks good dude! Keep the updates coming! Especially any more videos so we can hear it

[Kostamojen]

Wow someone local pulled off this swap! I've been waiting sooo long for someone to do it...

[Chromes]

all i have to say is WOW !

Owning a Legacy 3.0R 2009 i can vouch about the ''new style'' h6...
I've been trough STi,Xt,Wrx... Sure brute power wise and aftermarket wise, turbo h4 will always be a step ahead, but once you taste the ''smoothness'' and linear power delivery of the R it's hard to go back...As someone stated in a earlier post, looooong and smoooth snow drift is something really fun to do with the flat six :-)

The only downside with my legacy is the Automatic transmission that takes away a bit of the ''fun'' part :-/

I am happy to see that someone had to balls to do such a nice and different swap :-)

That's something i have been looking for to do in a forester 06-08 for a certain time...if you dont mind i would like to discuss in PM about technical/wiring part of the process :-)

Again Bravo my friend niccest project i've seen in a while !

[LucasBlack]

Originally Posted by Chromes

all i have to say is WOW !

Owning a Legacy 3.0R 2009 i can vouch about the ''new style'' h6...
I've been trough STi,Xt,Wrx... Sure brute power wise and aftermarket wise, turbo h4 will always be a step ahead, but once you taste the ''smoothness'' and linear power delivery of the R it's hard to go back...As someone stated in a earlier post, looooong and smoooth snow drift is something really fun to do with the flat six :-)

The only downside with my legacy is the Automatic transmission that takes away a bit of the ''fun'' part :-/

I am happy to see that someone had to balls to do such a nice and different swap :-)

That's something i have been looking for to do in a forester 06-08 for a certain time...if you dont mind i would like to discuss in PM about technical/wiring part of the process :-)

Again Bravo my friend niccest project i've seen in a while !

Thanks, Chromes! I really appreciate hearing about others taking joy from this build. I happened to hit up the Figure-8 set up at a recent track day, and I would like to confirm that yes, a RWD EZ36 Impreza can drift and it was fun, haha!

As for talking about the swap, feel free to PM me, and we can perhaps switch to email to keep the PM box from maxing out if the conversation gets lengthy.

[DougNuts]

I'm not familiar with the RWD Subaru conversions, do you have any concerns regarding the longevity of the rear differential now that it's not sharing the load?

Edit: Cool car BTW, this is the only direct-to-thread bookmark on my phone.

[LucasBlack]

Doug, funny you mention the rear differential -- my ring gear was apparently unhappy and lost a couple teeth while I was tracking the car at Laguna Seca this past weekend.

Interestingly, Impreza RWD conversions typically seem to call out the axles and the small pair of spider gears in the OEM diff as the typical weak points. I have a Cusco 1.5-Way Clutch Type LSD which I think is eliminating the weak spider gears as a possible breaking point, and I haven't had issue with the axles, though I'm not doing crazy clutch kicks and I don't have a huge amount of power.

My belief about the ring gear is that fluid temps in the diff were operating too high (not enough fluid capacity and no cooler for the high stress it was seeing from trackdays) and I think the ring gear just happened to be the first thing that fatigued from the heat to the point of breaking. I believe the fluid was reaching well North of 260*F, when a cap of 230*F is recommended from what I've read. We'll see if the actual diff is salvagable.

Glad you like the car!

[Seahawk]

Great build, very purpose built. Love the coolant overflow tank.

[LucasBlack]

Originally Posted by Seahawk

Great build, very purpose built. Love the coolant overflow tank.

Thanks! Yeah, the POM Juice gets the most attention from people glancing, ha!

[Patrick Olsen]

Maybe look into an R180 diff? I know it would kind of suck to have to make that step, since you've already put good money into the R160 in the form of the Cusco diff. I believe with some Legacy Spec B axles you could keep your 5x100 hubs, and as long as it comes from an STI the R180 will have some sort of fancy diff, so you wouldn't necessarily have to buy another Cusco.

[LucasBlack]

Pat, indeed, an R180 would be a step in the right direction, and I believe there are one or two ways to work out axles to be able to keep the 5x100 hubs (but would I also need a new driveshaft?)

And, I am unsure what sort of FD options I would have with the R180. I would hate to be stuck with a 3.90 FD with my 5 speed.

[Patrick Olsen]

You may be right on the R180 requiring a different driveshaft; since I stuck with my R160, I didn't have to worry about that when I went to the 6MT.

As for the final drive, I found one thread in which Rallispec said there is a 4.44 for the R180. Looking around online it appears there may be some Nissan options, as they used a version of the R180 in multiple vehicles "back in the day" (this site shows 4.11, 4.38 and 4.63). I say "may" because according to this thread there are different R180 versions (long vs short snout, plus different ring gear inner diameters), and that thread doesn't really make it clear which (if any) Nissan gears are actually compatible with the Subaru diffs.

[LucasBlack]

Originally Posted by Patrick Olsen

You may be right on the R180 requiring a different driveshaft; since I stuck with my R160, I didn't have to worry about that when I went to the 6MT.

As for the final drive, I found one thread in which Rallispec said there is a 4.44 for the R180. Looking around online it appears there may be some Nissan options, as they used a version of the R180 in multiple vehicles "back in the day" (this site shows 4.11, 4.38 and 4.63). I say "may" because according to this thread there are different R180 versions (long vs short snout, plus different ring gear inner diameters), and that thread doesn't really make it clear which (if any) Nissan gears are actually compatible with the Subaru diffs.

Good point about checking in with other manufacturers with regard to finding alternate FD gearsets; thanks for the leads!