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Old 10-11-2004, 12:11 PM   #1
BrysImpreza
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Default STi Intake Manifold on NA 2.5?

Just a question about the sizing and fit of an STi intake manifold. I know the 2004 NA 2.5 block is different from the STi's EJ257, but I was curious to see if the intake manifold would be a direct fit / swap onto a NA 2004 2.5

I was just hoping to let my TS breathe a little better with the bigger manifold. Will it cause any problems?

Thanx!

Bry.
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Old 10-11-2004, 02:20 PM   #2
Tim Sanderson
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There is no provision for the coil pack or the throttle cable bracket. You will also lose the holes for the injectors unless you use the tumble generator valves. Our n/a ecu's have no control for them so they will not open. You could use the tgv deletes and solve that problem, but then I think you would need a different fuel rail system.

The 04/05 us sti have coil on plug and throttle by wire.

By the time you add up the cost of making that work you could probably have it extrudehoned and powdercoated red.

Good luck

Last edited by Tim Sanderson; 10-11-2004 at 02:26 PM.
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Old 10-11-2004, 02:49 PM   #3
BrysImpreza
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Shoot, I forgot the STi and FXT were throttle by wire, ah well.

I'll stick with the stock PLASTIC intake manifold
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Old 10-11-2004, 03:05 PM   #4
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whats wrong with the plastic manifold, it has smoother inner walls, allowing for higher air velocity into the cyclinders, stays far cooler then a metal manifold would, cooler intake air, more hp, and its lighter to boot

theres not 1 disadvantage to having a plastic intake manifold, its actually a good thing
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Old 10-11-2004, 05:05 PM   #5
Tim Sanderson
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Ya, I'd take a plastic one.
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Old 10-11-2004, 05:12 PM   #6
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How about using a new plastic intake manifold in an old school impreza; would it fit, and would it provide any performance gains?
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Old 10-11-2004, 06:13 PM   #7
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Don't forget weight! . New Legacy GTs/ OB XTs have the plastic intake manifold and other plastic goodies

-paK +5
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Old 10-11-2004, 06:33 PM   #8
Tim Sanderson
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It's (i'm guessing) probably in the neighborhood of 5 pounds of weight savings. I think the benefit would be the smoother more consistant runners. The aluminum castings always have seems/flashing and are pretty rough to the touch. This may or may not create unwanted turbulence. I don't have a degree but something tells me that smoother is better in this instance.

Not sure if they would bolt up to older heads but I don't see why not.
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Old 10-11-2004, 08:12 PM   #9
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Quote:
Originally Posted by Tim Sanderson
There is no provision for the coil pack or the throttle cable bracket. You will also lose the holes for the injectors unless you use the tumble generator valves. Our n/a ecu's have no control for them so they will not open. You could use the tgv deletes and solve that problem, but then I think you would need a different fuel rail system.

The 04/05 us sti have coil on plug and throttle by wire.

By the time you add up the cost of making that work you could probably have it extrudehoned and powdercoated red.

Good luck
I always thought the STI didnt have TGVs?
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Old 10-11-2004, 09:05 PM   #10
Tim Sanderson
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I believe you are correct. I was mistaken in my first reply. I think the coil pack and perhaps the pcv and/or vacuum lines are different. And the fuel delivery problem.
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Old 10-11-2004, 09:07 PM   #11
subiekid
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and i think the mounting bolts are much different.
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Old 10-11-2004, 10:03 PM   #12
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Quote:
Originally Posted by powerlabs
How about using a new plastic intake manifold in an old school impreza; would it fit, and would it provide any performance gains?

it would fit afaik, but theres a cheaper easier way to get most of the performance gains (new manifodl is $$$). hondata intake manifold gaskets & throttle body mod.
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Old 10-12-2004, 12:26 AM   #13
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It fits on the 99+ SOHC heads. It will not fit the DOHC heads.....but an EJ20G manifold will!!!


Jay Storm
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Old 10-12-2004, 08:44 AM   #14
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spacers will help, but even with spacers your intake manifold will still get warm from the surrounding air in time, however i can touch my manifold even after 2 hours of highway cruising
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Old 10-12-2004, 01:38 PM   #15
Matt Monson
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I have an STi v6 intake manifold that I would consider parting with for the right price. It was going to be part of my NA build, but $$$ are short these days. As Jay mentioned, any of the post '99 EJ20 manifolds will fit post '99 EJ25 heads. The only trick I can see is plug wires, as the coil pack is offset like the older EJ25's. I do also have the wires that I would sell with it. I have the coil pack as well, but unless you want to cut and splice the connectors, it won't work with your stock harness. If you have an interest, send me a PM and we will take it from there...

EDIT: I almost forgot, getting the rails to fit will take a little rigging. The holes are much larger than yours and a thicker O-ring would need to be sourced to make it secure and sealed...
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Old 10-13-2004, 01:27 PM   #16
Tbird Man
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What about the 95 1.8L, ant plastic manifolds that fit that, also plastic is easier to modify to add things like NO2 and extra injectors.
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