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Old 09-29-2016, 10:50 AM   #1
Slynder
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Default 04 sti block with 07 sti head

Just did a leak down test and the head is bad instead of the block. Saved me a chunk of money to fix the head. The head will need either a new valve seal or valve.

Someone is selling a rebuild 07 sti head and I was just wondering if the head will fit the 04 sti block directly without modifying anything.

I would assume that if I do get the head I'll be needing a 07 sti head gasket, and different spark plug (Longer)?
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Old 09-29-2016, 11:03 AM   #2
Titter
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EJ207 Spec C 4EAT

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check the casting numbers. pre 2008 EJ257's use B25 heads. just make sure its the same B25 head you are buying.

B25 is single AVCS
W25 is dual AVCS

2008+ sti's should have W25 heads.

ensure the mating surface if perfectly flat. if not have it machined.

Last edited by Titter; 09-29-2016 at 11:09 AM.
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Old 09-29-2016, 12:36 PM   #3
mrsaturn7085
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There's more to it than this...

The AVCS system on the 2007 models was different. The center value of the PWM control was very different and I don't know if the 2004 ECU could accommodate the 2007 heads (w/o a standalone).

I'm not saying it *won't* work... but I'd be very careful with 2007 STI parts, in general. The 2007 was the black sheep of the USDM GD models.
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Old 09-30-2016, 07:20 AM   #4
Titter
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well if its just an ECU issue, couldnt he swap all his 04 sensors to the 07 head?
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Old 09-30-2016, 11:59 AM   #5
mrsaturn7085
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Again, more to it than this. The AVCS systems are different... in fact the whole 2007 engine is an oddball.

I wrote a lengthy explanation of this in an AVCS tuning thread, but I really doubt this will work. You could try swapping the ENTIRE AVCS system from the 04 to 07 heads and hope the cams are the same (again, I'm not sure - the AVCS tables are VERY different).

The center value I was referring to is a hard-coded PWM value that holds the cam position in a single locked level of advance. For the 04-06 EJ257, I believe it was 41% and held around 10-15 deg. Step a single % in either direction and the cam position will wildly change (i.e. 40% drops to 0 deg slowly, 39% slams the cam against the zero stop; 42% makes the cam climb to 50 deg slowly, 43% slams the cam against the 50 deg stop). The early EJ257's tendency to center around 10-15 deg is also why AVCS tuning past approximately 30-30 deg is not possible with these engines - the cam WILL advance to 50 deg, but cam movement is too quick past 30 deg to reliably select any position/advance value aside from 30 -or- 50; trying to pick something like 42 deg will cause instability as the ECU ends up hunting for the correct cam position and absolutely wrecking your VE stability (this is BAD and impossible to tune).

If this hard-coded value could be modified by the end-user, this would not be as much of an issue... unfortunately, none of the open source or Cobb maps have this open for tuning.

The problem here is the AVCS system is a dynamic VE adjustment to the engine. If you can't get the new heads (cams) to operate within about 5 degrees of the old cams at every position on the mapping, you will run into serious drive-ability (power, fuel economy, etc.) problems until you get it tuned (and even tuned, it will be sub-optimal if the ECU cannot accurately control the cams... you'd just be tuning around the electromechanical issue as a crutch).

Again, I'm not saying it 100% will not work... but from my experience setting up AVCS systems on standalone ECUs, the 04-06 EJ257 vs. 07 EJ257 vs. 06+ EJ255 vs. EJ207 are all different enough to need careful attention when using a standalone, and when using OEM ECUs for tuning, mixing and matching between these motors can be futile.

Last edited by mrsaturn7085; 09-30-2016 at 12:07 PM.
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Old 09-30-2016, 01:30 PM   #6
SoloWRXSTi
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To answer your question, yes it will. But the V25 heads are unique for 2007 (as mrsaturn eluded to above) in that they do not get the sodium filled exhaust valves. In my opinion, you'd be taking a step back from the 04 heads by going with the 07 heads. I would just send them to a reputable shop for rebuild.
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Old 10-06-2016, 09:22 PM   #7
Subie_
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Default 04 sti block with 07 sti head

Quote:
Originally Posted by mrsaturn7085 View Post
the whole 2007 engine is an oddball.
I have an 07 and this is 100% true. It's mostly the intake manifold, heads, engine harness and some quirks with the AVCS. The differences are fairly nuance and parts across years are generally interchangeable, however you're very likely to run into irritating and/or nearly inexplicable issues.

Quote:
Originally Posted by mrsaturn7085 View Post
You could try swapping the ENTIRE AVCS system from the 04 to 07 heads and hope the cams are the same (again, I'm not sure - the AVCS tables are VERY different).
I would venture to guess it will work, but it might not be optimal. I've noticed OCVs and cam caps between 06 & 07 matter significantly.
As far as cams are concerned, I can't speak to earlier years, but I've run 06 cams in my 07 heads no problem. I noticed 06 cams have a closed end cap whereas the 07 cams are "hollow" with an open end. I doubt this matters much though.
I don't recommend running one 04 head and one 07 head if that's what OP is suggesting.
Quote:
Originally Posted by mrsaturn7085 View Post
from my experience setting up AVCS systems on standalone ECUs, the 04-06 EJ257 vs. 07 EJ257 vs. 06+ EJ255 vs. EJ207 are all different enough to need careful attention when using a standalone, and when using OEM ECUs for tuning, mixing and matching between these motors can be futile.
I underestimated mixing & matching and learned the hard way... don't mix and match with 07. Parts are physically interchangeable, however this is potentially just the first circle of hell you're about to enter

Last edited by Subie_; 10-06-2016 at 09:39 PM.
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