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Old 06-09-2008, 05:17 PM   #1
MS WRX
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Join Date: Jun 2006
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Location: Jackson, MS
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Aspen White

Default STi head built

Tell me what ya'll think:

04 STi heads (keeping the AVCS)
3 angle valve-job
v.7 Spec C cams
Crower Valve springs
Mild port/polish

Prolly gonna run with a 20G

ideas? Critiques?
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Old 06-09-2008, 05:26 PM   #2
03WRX-WRB
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not really going to gain much, i dont know why your spending the money on the sti heads when they flow pretty good as it is. the 20g on an sti will make 380+ whp with good supporting mods

the stock WRX 2.0 head ive seen run well into the 400 whp range and work fine but yes an upgrade at 400 whp on the wrx heads is recommended but the sti heads flow more than enough and you probable wont see much of a gain
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Old 06-09-2008, 05:43 PM   #3
blowbyu24
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E85 pro comp sti

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if i have learned one thing about sti heads, its that the valves are the bottle neck....if you want just +1mm valves and do the springs and retainers with the cams...forget the porting
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Old 06-10-2008, 06:53 AM   #4
MS WRX
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^^^Thank you sir! Thats some handy information indeed
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Old 06-11-2008, 09:33 PM   #5
FuJi K
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NF Performance

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The valves are not the bottleneck. The INTAKE PORTS are the bottleneck on the USDM heads. Seems my power is holding all the way up top from 6400-7400rpms on my WRX heads w/ my EVO3-16G-8cm. Yes a bigger hotside, but my power doesn't taper off. I've also got 4-1 headers.

Of course the motor has all bolt-ons, but enlarging the intake ports will free up some more breathing up top. I always see WRX's with ALMOST the same MODS drop power up top. Ones with USDM STi cams help with that upper end, but mine made it there without STi cams.
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Old 06-12-2008, 06:41 PM   #6
kay95
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Ahh hate to say it but the bowl and seat areas are the biggest areas of improvement. The port area above the bowl and seat dont mean much because they flow alot more than the bowl and seat areas do. Just look at the size between the upper part of the port and the lower part of the port.


What you need is to get air by the seats in the mid lift range. That is where the valve spends most of its time. A good seat job on a motor without one stock can get a instant 15%-20% flow increase. Thats if its played with to get the most from the heads. You can still get a nice bump from the generic 30-45-60 most places put on.
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Old 06-12-2008, 07:24 PM   #7
MS WRX
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This is great info!! Thanks everyone
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Old 06-13-2008, 01:45 AM   #8
FuJi K
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Quote:
Originally Posted by kay95 View Post
Ahh hate to say it but the bowl and seat areas are the biggest areas of improvement. The port area above the bowl and seat dont mean much because they flow alot more than the bowl and seat areas do. Just look at the size between the upper part of the port and the lower part of the port.
Or say the FLOOR of the port runner. Opposite wall from the injectors.
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Old 06-13-2008, 05:49 PM   #9
kay95
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No not the floor. The bowl is the area just at the start of the short side radius to the seat. Its not just a wall its the entire area/volume. This is the bigggest choke point in any head out there next the the valve seat.
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Old 06-15-2008, 11:34 PM   #10
slowmike
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Quote:
Originally Posted by kay95 View Post
No not the floor. The bowl is the area just at the start of the short side radius to the seat. Its not just a wall its the entire area/volume. This is the bigggest choke point in any head out there next the the valve seat.
Is it best to open up the bowl around the valve guide or work on the floor at the short side radius?
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Old 06-16-2008, 04:30 PM   #11
FuJi K
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ah yes, the bowl. That's a important spot. There's usually a step there where the machine cut meets the port casting. Some heads come from the factory with a very bad bowl, some are fine. Subaru WRX/STi heads come pretty good, just touch it up a little bit to remove the step and you can also enlarge the FLOOR a bit to free up some up top. You can also take a bit out of that fat splitter too if you want.


The Integra Type R and Civic Type R get this part hand ported from factory before going into the car. Purchase a Type R head from HONDA and it will NOT be ported.


Quote:
Originally Posted by kay95 View Post
No not the floor. The bowl is the area just at the start of the short side radius to the seat. Its not just a wall its the entire area/volume. This is the bigggest choke point in any head out there next the the valve seat.
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Old 06-24-2008, 11:47 PM   #12
kay95
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Ya the valve guide is normally a good place to improve upon. There was a guy that did GT40 heads that saw a good gain from making the valve guides flush with the port wall. When he did that he got another 15% without any lost of flow anywhere. The guides stuck out a good bit though. I know the P1 2.2 heads I would have liked to do that to them because they stick out alot but its going into a DD.


If I could get one of those mini flow benches that would be awesome but I can only go off of others with different heads and setup til that happens.


Ahh here is the site. Its not a subaru head its a Ford 302 head but still same principles. Its a good read.

http://www.cmc.net/~xero/Mousesporting.html

Last edited by kay95; 06-25-2008 at 06:12 PM. Reason: forgot to add the web site
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