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Old 06-18-2005, 02:18 PM   #1
Impreza2003
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Default this might be dumb: but would an STi intake manifold fit on an NA 2.5RS?

I've seen a lot of people parting out their sti intake manifolds, im wondering if they would fit on my 2.5RS, we both have 2.5 liters but one is turbo one is not.

would it fit with out a lot of custom modification?

I guess the manifold would increase some more power and its really bling!

thanks
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Old 06-18-2005, 02:18 PM   #2
Impreza2003
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BTW my RS is an 03
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Old 06-18-2005, 02:25 PM   #3
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My guess? Fit, no. Power, unlikely. Bling, definitely, but at what cost? Paint your stocker red and call it a day, methinks.
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Old 06-18-2005, 03:17 PM   #4
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I don't believe it'd fit. Yea, just get your's powder-coated. Even if it'd fit, it would indeed be a waste of money without any substantial power gains.
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Old 06-20-2005, 06:47 PM   #5
Matt Monson
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Well,
It depends on what year. I have an STi v6 (MY00) intake manifold that will eventually make it's way onto my car. From '99 on, the Ej25's and Ej20's got the same bolt pattern. And the v6 one I have has larger runners that are going to flow better. But I won't be doing this until I have finished my 250+hp engine.

And one thing to be aware of with this is that you will need to switch the throttle cable over to the other side of the manifold, and find a place to put your coil pack...

And lastly, no you cannot use a USDM v8 EJ257 intake manifold. It is not the bolt pattern that is an issue. It is the throttle body. Your throttle body will not fit, and you cannot use the STi one because of the drive by wire...
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Old 06-21-2005, 12:20 AM   #6
Caplin 2.5
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even if you could fit it the diameter of the piping of the STi intake manifold is designed for a turbocharged vehicle and as i read somewhere ont his forum you will lose power on an N/A ej25 unless you got some serious mods and are pulling out 250+ hp
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Old 06-21-2005, 12:56 AM   #7
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interesting, thanks everyone

there goes another cool modd trampled down by the EJ25 engine!

im getting an STi next
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Old 06-21-2005, 03:21 PM   #8
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I feel you brother
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Old 06-21-2005, 04:44 PM   #9
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If you're any bit interested, look into intake manifold design. The runners are the length they are for a reason - it has to do with air pulses bouncing up and down the runners at a certain rate, and pushing or pulling other ones past the valves. Technically, every car has "ram air".
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Old 06-21-2005, 06:07 PM   #10
Caplin 2.5
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As I've found out by first hand experience making things specifically for your car is the best way to make power. First thing I would do is find out what the diameter of the stock STi manifold is, then find out the diameter of the stock RS manifold, then look up an aftermarket STi manifold copy the design with the RS diameter. You might be able to make your own custom intake manifold.
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Old 06-21-2005, 10:47 PM   #11
Patrick Olsen
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Quote:
Originally Posted by Caplin 2.5
even if you could fit it the diameter of the piping of the STi intake manifold is designed for a turbocharged vehicle and as i read somewhere ont his forum you will lose power on an N/A ej25 unless you got some serious mods and are pulling out 250+ hp
Not sure where you read that, but I beg to differ. Unless the STi intake manifold has more restrictive runners than the N/A 2.5L intake manifold (highly unlikely), there's no way you would lose power with an STI manifold. The power peak and power band may shift, but you certainly wouldn't lose power.

Quote:
Originally Posted by Caplin 2.5
...then look up an aftermarket STi manifold...
Can't say I've ever seen an aftermarket intake manifold for any of the various Subie engines. Is there something I've missed?

Pat Olsen
'97 Legacy 2.5GT sedan
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Old 06-22-2005, 01:28 AM   #12
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Magnus Motorsports makes an aftermarket manifold.....Maybe you missed it? :P

Their design may lend itself well to the NA crowd too (if it weren't so dam expensive)...


Jay Storm
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Old 06-22-2005, 06:13 AM   #13
X4 SRT
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Instead of using an STi intake manifold on our cars (which we can't) why don't we consider using the new intake manifolds on the 05 RS. From what I know they flow better than any of the other previous manifolds on RS's. If you look at them you can see that the runners are larger, and will obviously flow better. I think if you want to flow more air looking at this option is a very good idea. Then all you have to do is see if you can find some AVCS heads and an ECU to run them and your set. From another post I think it would be possible to find heads with AVCS for our cars. Think of all the possibilities.
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Old 06-22-2005, 06:15 AM   #14
Patrick Olsen
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Thanks, Jay, I had missed that. Wowzers!! $1200 for an intake manifold!!

Sure looks purty, though.
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Old 06-22-2005, 10:56 AM   #15
Matt Monson
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Quote:
Originally Posted by X4 SRT
Instead of using an STi intake manifold on our cars (which we can't) why don't we consider using the new intake manifolds on the 05 RS. From what I know they flow better than any of the other previous manifolds on RS's. If you look at them you can see that the runners are larger, and will obviously flow better. I think if you want to flow more air looking at this option is a very good idea. Then all you have to do is see if you can find some AVCS heads and an ECU to run them and your set. From another post I think it would be possible to find heads with AVCS for our cars. Think of all the possibilities.
Why do people always treat variable valve timing as some sort of magic pill? It is not a performance feature, it is an emissions feature. For the cost of getting AVCS to work, you can get a set of cams properly ground for real performance. Take the path of least resistence. Do you guys realize that the Rigolis have started using the SOHC EJ25 heads for their drag cars instead of the v8 STi heads they had been using before?
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Old 06-22-2005, 11:58 AM   #16
Patrick Olsen
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Quote:
Originally Posted by Matt Monson
Why do people always treat variable valve timing as some sort of magic pill? It is not a performance feature, it is an emissions feature. For the cost of getting AVCS to work, you can get a set of cams properly ground for real performance. Take the path of least resistence. Do you guys realize that the Rigolis have started using the SOHC EJ25 heads for their drag cars instead of the v8 STi heads they had been using before?
Welllll, it's not just an emissions feature. From what I've gathered with all of these variable valve timing and lift systems (Variocam, VVT, VVTi, VTEC, etc etc) one of the biggest benefits is a broadened power band. So, I guess I agree with you in that peak power won't change much, if at all, but the good ol' "area under the curve" can be substantially better.

Pat

PS - empty some space in your PMs, compadre, so I can respond to your response.
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