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Old 06-01-2012, 10:06 AM   #26
Nuul
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Thanks for posting this, good info for those of us about to start a hybrid project.
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Old 06-01-2012, 02:55 PM   #27
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Quote:
Originally Posted by Jirv311 View Post
So if stock STi compression is 8.2:1 and I use 8.5:1 pistons with 02 WRX heads undecked, stock STi head gaskets, what CR am I looking at? I've heard with stock STi pistons (at 8.2:1) it's around 8.96:1-ish so would 9.26:1 sound about right?
Probably around there. The big problem with a 257 block and 205 heads is not the higher CR IMO, but the weird knock issues you run into as the 205 combustion chambers are not designed for the 257 pistons. Homemade WRX brought up the point that custom pistons designed for the 205 combustion chambers should work, but I don't know of anyone that's tried it yet.
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Old 06-01-2012, 08:19 PM   #28
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Originally Posted by KpT KiM View Post
Probably around there. The big problem with a 257 block and 205 heads is not the higher CR IMO, but the weird knock issues you run into as the 205 combustion chambers are not designed for the 257 pistons. Homemade WRX brought up the point that custom pistons designed for the 205 combustion chambers should work, but I don't know of anyone that's tried it yet.
I think the knock issues probably come more from the sharp edges of the combustion chambers and are more prominent due to their position within the cylinder on a hybrid. I'll be rounding mine out.
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Old 06-01-2012, 08:47 PM   #29
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I'd seriously consider cnc work on the heads. Any unevenness will create hot spots, and minor differences between cylinders is problematic as well. Another thing to keep in mind is the quench surface dimensions and difference between 92mm and 99.5 mm piston quench area.
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Old 06-01-2012, 08:49 PM   #30
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Originally Posted by Jirv311 View Post
I think the knock issues probably come more from the sharp edges of the combustion chambers and are more prominent due to their position within the cylinder on a hybrid. I'll be rounding mine out.
Let me know how that works i bet if you take your 257 head gasket and lay on the heads and scribe a line you could carefully smooth out the sharp edges of the mismatch and be ok.
I work in a CNC shop so when i get to doing my build i am going to mill out the sides of the head where the gasket lines up to and make it close to the 257 heads. if i get crazy i will make up a plexi glass head chamber tester to see what the CC's are.
And I would say you would be safe with running 8.5:1 pistons or 9.0:1 if you are going to smooth out and remove some material on the heads. i read that a 257 block with 205 heads is more like 8.8:1 so with 8.5:1 pistons you would be like 9.1:1 which would be good. remember factory subarus run very low cr for being turbo and as others have said they run 9.5:1 and love it probalby give more low end power.
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Old 06-01-2012, 09:39 PM   #31
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My last hybrid motor was a basic 257 SB with my shops custom Wiseco pistons and the CR was 8.5:1 with WRX heads. I did have cams which lower your effective CR and the combustion chambers, valve faces, and exhaust ports where ceramic coated. On 91 California octane I had no knock issues, made great power, and the car was the smoothest revving Subaru engine I personally have ever driven.

That same engine is in my STi currently just waiting for my turbo so I can get the car running. The only difference this time around is the heads aren't ceramic coated this time. Will I be more prone to knock now? Probably just not sure by how much, I'll report back for a comparative data point.


Those who have been around have been running hybrids for some time know that there are more than one way to skin a cat and while the combustion chamber mod is good and does work there are also other effective ways to get a great running hybrid.
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Old 06-02-2012, 03:11 AM   #32
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Quote:
Originally Posted by wrxkid2003 View Post
Let me know how that works i bet if you take your 257 head gasket and lay on the heads and scribe a line you could carefully smooth out the sharp edges of the mismatch and be ok.
I work in a CNC shop so when i get to doing my build i am going to mill out the sides of the head where the gasket lines up to and make it close to the 257 heads. if i get crazy i will make up a plexi glass head chamber tester to see what the CC's are.
And I would say you would be safe with running 8.5:1 pistons or 9.0:1 if you are going to smooth out and remove some material on the heads. i read that a 257 block with 205 heads is more like 8.8:1 so with 8.5:1 pistons you would be like 9.1:1 which would be good. remember factory subarus run very low cr for being turbo and as others have said they run 9.5:1 and love it probalby give more low end power.
Low end is definitely something I'm hoping for on this one. It's a bit pathetic how weak the 2.0 is by itself right now.

I'll throw some pictures up once I clean up the heads and we'll see how it works.
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Old 06-12-2012, 06:10 PM   #33
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i had a pnp'd sti heads with 272s springs valves and retainers in my car but recently removed them so i could daily the car now so im putting 02 wrx heads on a fully built ej257 bottom end, timing setup is from an 02 wrx, heads are stock. ill be firing the car up for the first time on friday after school lets hope all goes well haha
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Old 06-12-2012, 06:41 PM   #34
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Quote:
Originally Posted by swagwag92 View Post
i had a pnp'd sti heads with 272s springs valves and retainers in my car but recently removed them so i could daily the car now so im putting 02 wrx heads on a fully built ej257 bottom end, timing setup is from an 02 wrx, heads are stock. ill be firing the car up for the first time on friday after school lets hope all goes well haha
Why couldn't you DD the car with the 272s in it?
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Old 06-12-2012, 07:20 PM   #35
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^Bad tune maybe?... 272's are perfectly streetable.
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Old 06-12-2012, 08:16 PM   #36
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not that the tune was bad but the car wasnt the best on gas...especially in boost which you cant help but hit lol, i actually have the heads forsale now if you huys know anyone thats interested. i really need some cash as well
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Old 06-13-2012, 12:05 AM   #37
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Quote:
Originally Posted by swagwag92
the car wasnt the best on gas...especially in boost which you cant help but hit lol
that's not the cam's fault, that's you. lol your right foot determines how much gas the engine is going to suck up.
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Old 06-13-2012, 11:16 AM   #38
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subscribe
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Old 06-13-2012, 11:56 AM   #39
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Quote:
Originally Posted by ronzogonzo View Post
2L heads use 2L plugs

-Phil
...And if your ej205 heads are cut to match the ej255 combustion chambers...you still use spark plugs from the ej205.

Just in case anyone wanted to know.
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Old 07-07-2012, 08:25 PM   #40
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Quick question about my build. I'm moving to the 06 STi oil pan and pickup and wondering if I have to use the STi windage tray or can I still use my 02 WRX one?
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Old 07-08-2012, 11:56 AM   #41
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Quote:
Originally Posted by Jirv311 View Post
Quick question about my build. I'm moving to the 06 STi oil pan and pickup and wondering if I have to use the STi windage tray or can I still use my 02 WRX one?
I actually went with the Killer B windage tray, it's a really nice piece for a reasonable cost. I'd go that route personally.

I just finished putting about 3k on my new hybrid build, and it's been fantastic. Doesn't burn a drop of oil, it's quiet, and makes good power. I'm running:

09 EJ255 LGT block, 99.75mm Mahle 4032 pistons, ACL bearings, Eagle rods, STi nitrided crank, CnC'd 205 heads done by ASF machine, stock STi HGs, and a VF34. It's a fun DD!
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Old 07-08-2012, 01:31 PM   #42
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Quote:
Originally Posted by 03SubyWRX

I actually went with the Killer B windage tray, it's a really nice piece for a reasonable cost. I'd go that route personally.

I just finished putting about 3k on my new hybrid build, and it's been fantastic. Doesn't burn a drop of oil, it's quiet, and makes good power. I'm running:

09 EJ255 LGT block, 99.75mm Mahle 4032 pistons, ACL bearings, Eagle rods, STi nitrided crank, CnC'd 205 heads done by ASF machine, stock STi HGs, and a VF34. It's a fun DD!
That build does seem fun!! Very close to what I'm currently building (except a 05 STi block and a precision 5858)

What power do you put down? Are you in the power band or top end? Either way... watch out for those pestering po-po!!
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Old 07-09-2012, 08:20 PM   #43
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Originally Posted by Jirv311 View Post
Quick question about my build. I'm moving to the 06 STi oil pan and pickup and wondering if I have to use the STi windage tray or can I still use my 02 WRX one?
You could use your '02 WRX one, but the '02 WRX windage tray is very restrictive. Oil doesn't return to the pan quickly.

The KillerB version is only ~$70 and will let oil flow back the pan quickly, which is the way it was deliberately designed.
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Old 07-16-2012, 08:35 AM   #44
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Ok, i realised that there are 2 different Front 02 sensors, theres one for the JDM 207 and then theres a different one for the US ej257.
AFter having rebuilt my ej207 using a the 257 bottom end, with my jdm heads, im now wondering which 02 sensor to USe.
Do i go with the 2.0jdm sensor (22641AA042) or do i use the 2.5US sensor (22641AA211), i have been having idling issues and was wondering if this could be the ONE of the causes.
Any thoughts?
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Old 07-16-2012, 09:01 AM   #45
kellygnsd
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It all depends what ecu and wire harness you have. The engine/head combo matters not.
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Old 07-16-2012, 09:18 AM   #46
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still running my stock 2004 jdm ECU, i had a ej207 in there and simply swapped out the bottom end for an ej257 with forged pistons.
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Old 07-16-2012, 10:39 AM   #47
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You need the jdm sensor. If that's the one you have maybe your idle problems are tune related
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Old 11-24-2012, 11:22 PM   #48
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i was looking for a ej257 short block and found a complete longblock for a good price. it has single avcs. so is it possible to still use these heads and maybe change out the cams for non avcs 2.5L cams? or would it be best to just part the heads complete, cnc the 2L heads and get somethign like a Crower 272 for a 2L
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Old 11-25-2012, 12:32 AM   #49
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Run as is without AVCS
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Old 11-25-2012, 12:43 PM   #50
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i was told that wouldnt work..hmmm
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