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Old 06-01-2004, 05:50 AM   #1
awd4ever
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Default intake manifold improvements over the years

I've searched, but was unable to find any benefits to using an STI intake manifold over a 98rs one for my project. Are there are benefits to having STI manifold (besides the color)?

Thanks
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Old 06-01-2004, 07:07 AM   #2
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No, unless its a ver 8, they are a different design. Side note the ver 8 STis run the same plug in all 4 holes, while the ver 7 with the older manifold runs a hotter plug in number 4...
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Old 06-02-2004, 02:08 AM   #3
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i am not sure i follow you.. are you talking about spark plugs? they dont go into intake manifold

Reason i am asking, is i am trying to get the calculations out of the way before I start spending money on parts, and with ~20-22psi planned I want the most volume from intake mani.

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Old 06-02-2004, 03:24 AM   #4
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well an sti intake manidold would give you more room for an intercooler.

will the v8 sti manifold fit onto a set of 98 dohc heads? i dont think they will, but what ever.
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Old 06-02-2004, 02:59 PM   #5
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Quote:
Originally posted by awd4ever
i am not sure i follow you.. are you talking about spark plugs? they dont go into intake manifold

Reason i am asking, is i am trying to get the calculations out of the way before I start spending money on parts, and with ~20-22psi planned I want the most volume from intake mani.

Thanks
Get a worked manifold...

I was talking about the plugs... number 4 runs hotter then the other cylinders. And some belive its becase of the old manifold.
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Old 06-02-2004, 08:26 PM   #6
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so does the v 8 sti manifold fit into a set of dohc heads?
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Old 06-02-2004, 08:38 PM   #7
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Quote:
Originally posted by subiekid
so does the v 8 sti manifold fit into a set of dohc heads?
DOHC heads, well the sti has DOHC heads... I dont know how different they are vs the older DOHC heads. Other then the AVCS...
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Old 06-02-2004, 10:49 PM   #8
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Hmm, I always thought the new intake manifolds for the wrx/sti would not fit onto the older DOHC heads. I might have to do some research.
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Old 06-02-2004, 11:42 PM   #9
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I have it from a pretty good source that the USDM '98 DOHC EJ25 heads use the same cores as the '97-99 JDM EJ20K's. They are a big bore with different cams, springs and valves. I can't tell you if they used the same manifold or not, but it wouldn't make much sense to make a new manifold for old cores.

I have also been told that EJ207 manifolds do not line up correctly to EJ20K heads, so a V7 or V8 manifold would likely not fit. But the fact of the matter is that on a FI build, the stock manifold is not going to be a major restriction and doesn't neeed any time or money spent trying to figure out a solution for running 20-25psi...
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Old 06-03-2004, 11:13 PM   #10
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Extrude honing your existing manifold is really the way to go. Plus with the older manifolds you don't have to deal with all that TGV crap.
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Old 06-03-2004, 11:53 PM   #11
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I thought I remembered cobb doing some flow bench stuff on the old manifolds and saying that modifying the manifold is not really worth it for the minimal power gains. I also seem to remember something about the unequal length of the runners causing different cfm's at each runner making certain cyliners run hotter. Maybe a custom equal length runner manifold is in order- but not for 20 psi. YOu should be fine with the stock manifold at those boost levels.
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Old 06-04-2004, 07:41 PM   #12
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Quote:
Originally posted by Drac9
I thought I remembered cobb doing some flow bench stuff on the old manifolds and saying that modifying the manifold is not really worth it for the minimal power gains.
I spoke with Josh at Cobb about this last weekend regarding my NA build and that is exactly what he said. He said that when they cut a manifold to access all parts of the runners during porting and then re-welded it together they saw about a 3% gain in flow. Not worth the effort in my mind, especially on a boosted build...
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Old 06-05-2004, 01:25 AM   #13
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Quote:
Originally posted by totoherbs
Get a worked manifold...

I was talking about the plugs... number 4 runs hotter then the other cylinders. And some belive its becase of the old manifold.

I thought it was fuel related, what with the rails being parallel and all that.
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Old 06-05-2004, 01:38 AM   #14
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I think you're referring to series. The third cylinder is last in the series configuration. Parallel is what you want in ragards to fuel distribution.

-Brett
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Old 06-06-2004, 09:22 PM   #15
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thank you guys, this info has been really helpfull. And it goes in line with what local shops told me.
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Old 06-07-2004, 04:35 PM   #16
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I wanna see someone get the 04 2.5 RS/TS manifold and take some intake temp readings.....it's GOTTA be colder since it is plastic!

I'd be REALLY interested in the comparison results.
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Old 06-07-2004, 05:07 PM   #17
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One thing that does help these manifolds a lot is phenolic spacers. Cuts manifolds temps a lot.
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