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Old 03-31-2005, 10:55 PM   #1
Discjoshie
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Default Ported Intake Manifold

I am deciding what to do for a higher power and torque NA build for my 2000 RS. I am definitely going to go for TWEs stage II heads, stage II cams, and valvetrain upgrade. I will probably get some sort of built shortblock, hopefully with a larger displacement, in the future (going for a torquey street motor). I was originally not going to touch the intake manifold because of what I read in one of Cobb's older tech articles about building up a reliable street motor (precisely what I am going for). They said that it could use some polishing but it doesn't pay to crack it open and then reweld it. The gains would not be worth it. Elsewhere I have read that the intake manifold is actually the bottleneck of airflow in the SOHC ej25. Would it actually be worth having the manifold ported and polished etc. considering the trouble? What about the P&Ped red powdercoated manifold that xcceleration is offering for $300? What sort of gains would this yield with TWE heads and cams, Cobb intake, Cobb equal-length headers with cat and catback?

-Josh
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Old 03-31-2005, 10:59 PM   #2
Tim Sanderson
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The newer rs's use a plastic intake manifold that have smooth runners. I'd look into that. Otherwise the best option which is also one of the most expensive is to have it extrudehoned. I believe it's about 375$ to have it done.
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Old 04-01-2005, 01:03 AM   #3
Honkey3k
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uhm, i think my rs is pretty new..... 2005.... and i dont have a plastic manifold. However, the 05 manifold is much bigger than previous years
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Old 04-01-2005, 01:47 AM   #4
zzyzx
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Hmm, the plastic intake manifold must have been an experiment of sorts for '04. I've got one on my '00. It's so much smoother than the cast one it's not even comparable...
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Old 04-01-2005, 11:33 AM   #5
Honkey3k
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hmm. Anyways, I suggest looking into 05 manifolds, they have different crap running different places, like my ignition dingy is on the back side of the manifold rather than on top. Ill get a pic tonight after work.
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Old 04-02-2005, 12:51 AM   #6
HamFist
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I think the runner placement changed if I remember looking at it right. The runners sit differently in relation to each other. It makes a circular swirl pattern in the manifold plenum, I think...
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Old 04-03-2005, 11:06 AM   #7
Slack
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I was looking under the hood of an 05 OBS yesterday, and while the manifold was not plastic, it was a totally different design than what I'm used to seeing. The tubes didn't spread out like a spider, but were stacked two on top, two on bottom. I wish I had taken a pic with the camera phone for reference. Maybe next time I'm at the dealership.


Mick
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Old 04-03-2005, 11:52 AM   #8
AutoAviat
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Quote:
Originally Posted by Slack
I was looking under the hood of an 05 OBS yesterday, and while the manifold was not plastic, it was a totally different design than what I'm used to seeing. The tubes didn't spread out like a spider, but were stacked two on top, two on bottom. I wish I had taken a pic with the camera phone for reference. Maybe next time I'm at the dealership.


Mick

I've got one...my Saab 92x (same is 2005 RS).

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Old 04-03-2005, 12:25 PM   #9
Slack
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I'm getting an error when trying to access that URL.


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Old 04-03-2005, 01:56 PM   #10
Caplin 2.5
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what is "extrudehoned"?
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Old 04-04-2005, 03:36 PM   #11
Section 8
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What happens to your ass when you eat to much fiber.

Same idea with abrasive putty forced through the manifold.
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Old 04-04-2005, 03:41 PM   #12
powerlabs
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Quote:
Originally Posted by zzyzx
Hmm, the plastic intake manifold must have been an experiment of sorts for '04. I've got one on my '00. It's so much smoother than the cast one it's not even comparable...

Did you notice much difference. How much did it cost you?
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Old 04-04-2005, 03:58 PM   #13
omahasubaru
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http://www.extrudehone.com/

I know a local vendor who offers this service. May be worth while. Some coatings may help you out with heat resistance if you don't go to the plastic IM.
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Old 04-04-2005, 04:34 PM   #14
Discjoshie
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So would a plastic or extrudehoned manifold really help to unrestrict flow and result in more power? I am not just looking for smooth for the sake of smoothness. I am wondering if getting a throttle body that has been bored, ported, polished, etc. will really be worthwhile in an NA buildup.
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Old 04-04-2005, 06:58 PM   #15
Section 8
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Use a WRX manifold. It has significently larger runners than the NA manifolds to begin with.
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Old 04-05-2005, 02:58 AM   #16
poormansporsche
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I thought I heard the WRX manni wont fit unless you have WRX heads. And even then you had to custom fit stuff.

cheers

garrett
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Old 04-05-2005, 09:23 AM   #17
Section 8
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It fits fine. The poster says that he is porting the heads, and that is the only fitment problem with the WRX manifold. If you gasket match the intake port to the WRX intake gasket instead of the RS gasket you are set. TPS can be rewired(they are both 3 wires, the plugs just do not fit), stick the map/temp sensor in the manifold, and cut off the IAC from the RS throttle body and plump lines from infront of the throttle body to the manifold through it. Then mount the coil pack somewhere.

You can not just bolt it on to stock RS heads and have it work though. I don't see how this would be any more work than farting around with one of the new manifolds where things are different as well (for one, there is no MAPtemp sensor so you are already looking for a place to mount it on the new manifold anyway).
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Old 04-05-2005, 10:20 AM   #18
Caplin 2.5
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Is bigger diameter pipes for the intake manifold a good thing on a N/A?
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Old 04-05-2005, 12:01 PM   #19
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Yes. But as always... with-in reason
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Old 04-05-2005, 02:28 PM   #20
Section 8
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Quote:
Originally Posted by Caplin 2.5
Is bigger diameter pipes for the intake manifold a good thing on a N/A?
My post is only in the context of the thread and what the original poster stated he was going to do. If you are thinking of raising the redline, it will be good. If you are using stock cams you would be better off with the stock manifold. You don't HAVE to anything until you get up around 7,000 RPM or more. Cobb figuers this is the upper limit of flow of the stock manifold and DCoty figuered this as well, both with running engines.

Different parts will require different angles of attack.

Using generalizations is the devil talking. THE DEVIL TALKING!

Also, shorter rods with larger bore diameter can benifit from slightly larger than "optimal" ports/valves due to the quick acceleration of the piston from TDC.
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Old 04-06-2005, 10:38 AM   #21
omahasubaru
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Yes, but there is more to look at the intake manifold than just flow.

Increasing the inner diameter will help increase the torque as long as you aren't making the runner longer or anything (which in this case you obviously aren't).

Sure I'm thinking about DSP/FSP autocross rules and gains to get, but it wouldn't hurt by any means. There are still many better things to spend your money on, but it's an option none the less.
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Old 04-06-2005, 11:30 AM   #22
Section 8
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Huh?

SHow me where I said (or inferred) that it would be bad?

Again, the post was only in the contest of what the original poster was talking about.

You don't want to start an intake manifold discussion with one sentence, with zero qualifiers.
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