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Old 05-31-2009, 12:15 PM   #1
billydekid87
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Default 2.5 Boost

Ok simple question here. How much HP can a stock 2.5 hold.I know they are fragile. I just want an estimate.


Reason I am asking is I have a bud that wants to get rid of his WRX turbo. And I was looking for one
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Old 05-31-2009, 03:36 PM   #2
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its reallly reallly risky because of the high compression other little factors. it can definitely be done tho. i wonder if you can just bolt on the exhaust manifold, up pipe, intake, etc to make it easier. good luck
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Old 05-31-2009, 05:25 PM   #3
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True about the higher compression, any other advice? I am still on the fence about it..

I am not sure if they would bolt up, it would be nice. If not I can weld. lol
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Old 06-01-2009, 03:20 AM   #4
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2.5i or RS open deck blocks can take about 350 to the wheels thats about close to 400HP I'm sure sleeved block will yeild you more and still be opendeck..as for STI internals it'll work rememeber its still 99.5mm pistons eve nif compression is lower just remember t ojust get forged 9.0:1 pistons for that turbo less boos still more power means turbo running better and longer.
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Old 06-02-2009, 03:17 AM   #5
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I wish everything like the intak mani, and exhaust just bolted on to our blocks, I would pry be boostin right now. Idk if I was you it would be easier to do a swap I have came to this conclusion. I mean the Aveo turbo kit is 4k ALONE. Yea screw that I can pick up a rear ended wrx for about 6k and do suspension and drivetrain to. I mean look at your choices and the up's and down's. You throw a turbo on your stock motor and pop it. Your out of a car for a while unless you have more than one. But if that's the case i would just say take your time and swap it. Just my 2 cents. Just fallow your heart and your waller But either way have fun and let me know what you do.
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Old 06-02-2009, 07:41 PM   #6
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Exhaust does bolt right on, but the uppipe doesn't clear the crossmember. But you can get the turbo crossmember, it bolts right up.
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Old 06-03-2009, 02:48 PM   #7
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why don't you force feed the bitch and find out ???
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Old 06-03-2009, 06:46 PM   #8
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Quote:
Originally Posted by VIsubi View Post
2.5i or RS open deck blocks can take about 350 to the wheels thats about close to 400HP
where did you get this information from? i'm just curious because i want to turbo my 2.5i, but i do not want to touch the internals. hence i think realistically i can only make 260 at the CRANK. do you mean a built 2.5i block?

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Exhaust does bolt right on, but the uppipe doesn't clear the crossmember. But you can get the turbo crossmember, it bolts right up.
would it be easier and cheaper to just have the stock up pipe modified to fit rather than installing a new cross member? I saw someone use a legacy turbo cross member on a 2.5rs i think, but i thought it would be trivial and reasonably cheap to have someone make the up pipe fit. is there some reason why this can't be done?
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Old 06-03-2009, 07:12 PM   #9
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where did you get this information from? i'm just curious because i want to turbo my 2.5i, but i do not want to touch the internals. hence i think realistically i can only make 260 at the CRANK. do you mean a built 2.5i block?



would it be easier and cheaper to just have the stock up pipe modified to fit rather than installing a new cross member? I saw someone use a legacy turbo cross member on a 2.5rs i think, but i thought it would be trivial and reasonably cheap to have someone make the up pipe fit. is there some reason why this can't be done?
you REALLY need to SEARCH !!! This has been covered only about 1,000,000 times.... give or take.

Most people feel that an otherwise unmodified NA phase 1,2 whatever EJ25 will reliably handle up to around 10lbs of boost before you want to start upgrading internals. The ej25 has the weakest rods of any ej series engine as it has the longest stroke. The ej22 and 18 have been known to handle a little more boost, but simply don't have the bottom end, or torque of the RS block.

The open deck nature of our blocks is quite a controversial subject, as few have had failure caused by "ovaling" of their cylinder walls at high combustion chamber pressures....IE 20+lbs. This is very rare though because it is much more cost effective to simply do a swap or buy a semi closed deck STI block than to even bother swapping internals on their open deck block anyway.

As far as running a wrx settup, if you want to go 100% wrx bolt on, you will need a wrx waterpump & crossmember if you go that route. BUT installing the wrx crossmembers is quite a PITA due to having to add spacers to get it to fit correctly. The best way to go would be to find yourself a nice set of up & down pipes designed for your RS, this will allow you to place your turbo in a better position for fabricating your own intake. Remember the WRX has tumble valves which raise their intake manifold quite a bit, allowing their intake to run right under it.....horrible idea IMO. You would not be able to run a wrx intake anyway...

Another route that people go is to Notch their cross members. You simply cut out a half circle allowing room for the up pipe. Then find some NICE thick tubing a little bigger than your uppipe. You cut it in half, and weld that small section inside the circle you cut in your xmember. This actually strengthens your xmember quite a bit. IIRC, this way allows you to use a wrx up pipe on your headers without needing to replace your waterpump. I don't remember if the flange had to be clocked or not... again, you might wanna do a search.

ALL the info you want is in this forum.... SEARCH !!!
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Old 06-03-2009, 07:29 PM   #10
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I have been, but thanks, that helped a lot. I get lost in a single thread for 2 hours... I've decided to back off anyway and buy some books instead. I need to learn more about engines first because while I might be able to pull off installing the basics, I doubt I could fix anything that goes wrong.
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Old 06-03-2009, 09:03 PM   #11
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Great info! Thanks guys, I had a HP limit in mind of around 220. Which would be enough for me. So I could probably safely run a wrx setup , with modification, to about 10lbs of boost. I plan on getting another engine probably ej20 later on. But I want to plug and play haha.

I can figure something about about the fitment, Nothing a little cutting and rewelding cannot fix.
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Old 06-07-2009, 03:37 PM   #12
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Quote:
Originally Posted by billydekid87 View Post
Great info! Thanks guys, I had a HP limit in mind of around 220. Which would be enough for me. So I could probably safely run a wrx setup , with modification, to about 10lbs of boost. I plan on getting another engine probably ej20 later on. But I want to plug and play haha.

I can figure something about about the fitment, Nothing a little cutting and rewelding cannot fix.
If you want 220 horse at the crank, you don't need any WRX internals, any stock 2.5 NA block will do that (you're looking at 5 pounds to achieve that power with high compression). If you run 10 pounds at high compression you're looking at closer to 260+ horsepower at the crank, and even more torque, while of course being at a higher risk for kaboom
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Old 06-07-2009, 10:57 PM   #13
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you can get 220 @ the crank without a turbo... throw in some high compression pistons, Light weight EVERYTHING, Flywheel, crank,PS & alt pulleys along with a nice high reving valvetrain with some high lift/duration cams and you'll be all set !
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Old 06-08-2009, 03:18 PM   #14
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Quote:
Originally Posted by IllNastyImpreza View Post
you can get 220 @ the crank without a turbo... throw in some high compression pistons, Light weight EVERYTHING, Flywheel, crank,PS & alt pulleys along with a nice high reving valvetrain with some high lift/duration cams and you'll be all set !
Please PLEASE trust me on this one...leave the crank pulley alone. Just upgrade the accessory pulleys but for gods sake...leave the crank pulley as it is.

Trust me
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Old 06-08-2009, 06:24 PM   #15
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why leave the crank pully alone?
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Old 06-09-2009, 12:37 AM   #16
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why? I've had ALL lightweight pulleys, and a 14lb flywheel for years without any problems.... Then again my motor is balanced and blueprinted
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Old 06-09-2009, 01:39 AM   #17
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The crank pulley is also a torsional vibration damper. just look at the rubber piece, it seperates the belt surface from where it bolts to the crank. it prevents crank twist which saves bearings. you don't have to have them its just a good idea
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Old 06-11-2009, 04:03 PM   #18
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The crank pulley is also a torsional vibration damper. just look at the rubber piece, it seperates the belt surface from where it bolts to the crank. it prevents crank twist which saves bearings. you don't have to have them its just a good idea
Though I think the general consensus around here is that on a 200hp NA motor you won't be breaking anything by not having the vibration dampener.
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Old 06-11-2009, 05:13 PM   #19
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The crank pulley is also a torsional vibration damper. just look at the rubber piece, it seperates the belt surface from where it bolts to the crank. it prevents crank twist which saves bearings. you don't have to have them its just a good idea
This has been discussed THOUSANDS of times. With the design of our horizontal motors being much more balanced than any inline, or V design, the harmonic and other vibration dampening effect of our pulleys is simply NOT an issue.

Does the pulley dampen vibration and whatnot? YES it does...

Does removing it for a pure aluminum pulley vastly effect the longevity of your motor? No it doesn't. Tons of people have had lightweight pulleys on their Subarus for decades without problems !

Again... I have both a 14lb flywheel, AND ALL aluminum pulleys...with ZERO problem
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Old 06-12-2009, 03:27 AM   #20
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Balance isn't the issue because the pulley is not an external balancer. I'm talking about harmonic frequency, not balance vibrations...i.e. on a swing, you kick your legs around and hit the right frequency...you're swinging. a firing cylinder is not a smooth event, rather a controlled explosion. The crank deflects and reflects at every firing event and at higher rpm's those deflections get pile on and create greater flexing. And why are some of those inferior inline and v engines able to spin up to 9k in stock trim while not many subarus live long up there....and yes, way off the point of a 2.5 with 200hp. it probably couldn't care less if there even weren't a pulley on there but I'm just trying to get a small point across...."you don't have to but it's a good idea" and for some odd reason, high end dampers can and have increased horsepower.

Last edited by front runner; 06-12-2009 at 03:33 AM.
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Old 06-12-2009, 08:10 AM   #21
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Quote:
Originally Posted by front runner View Post
Balance isn't the issue because the pulley is not an external balancer. I'm talking about harmonic frequency, not balance vibrations...i.e. on a swing, you kick your legs around and hit the right frequency...you're swinging. a firing cylinder is not a smooth event, rather a controlled explosion. The crank deflects and reflects at every firing event and at higher rpm's those deflections get pile on and create greater flexing. And why are some of those inferior inline and v engines able to spin up to 9k in stock trim while not many subarus live long up there....and yes, way off the point of a 2.5 with 200hp. it probably couldn't care less if there even weren't a pulley on there but I'm just trying to get a small point across...."you don't have to but it's a good idea" and for some odd reason, high end dampers can and have increased horsepower.
1) where would you purchase one
2) in another thread about the perrin pulley someone contacted SOA and they said it wasn't a damper of any sort (assuming the letter was real of course) http://forums.nasioc.com/forums/showthread.php?t=437237 go down to post 25.
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Old 06-12-2009, 09:26 AM   #22
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Hmm! I needed to mount a dry sump drive on my pulley and the dampening material was in the way. I got on ebay and found a WRX pully for 5 bucks and it did not have the rubber at all. So why on the RS and not on the WRX.
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Old 06-12-2009, 10:18 AM   #23
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i have a built open deck ej251 block with mahle 8.5:1 pistons in it, sti rods, arp rod bolts, cometic head gaskets, and arp head studs. head work i have all stock head with delta turbo regrind cams. Im running 15 psi right now on a GReddy T518z 18G with a tial 38mm ewg and its a fun car!!! ive seen no problems n its been driven hard for the last 5 months or so on this setup. Ive got a Greddy profec B-II ebc awaiting installation and i plan on running 20+ psi. i know guys on rs25 have pushed the open deck N/A block past 500awhp!!! i would think as long as your block is in good condition and you have the proper cooling system, oiling system, and tight clearances then open vs. closed deck shouldnt be of concern to most on this board. obviously if you have access to a semi closed or fully closed setup its ideal - but open deck can be done just fine.
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Old 06-12-2009, 10:45 AM   #24
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... And why are some of those inferior inline and v engines able to spin up to 9k in stock trim while not many subarus live long up there.......
some day the brilliant engineers @ Subaru might be able to figure out a crank oiling design that DOESN"T starve @ high rpm

Right now just about the only thing you can do is cross drill your crank... or run a dry sump system. Personally I don't care for an engine that runs 20 quarts of oil and takes 1/2 hour to warm up
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Old 06-13-2009, 12:44 AM   #25
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Ati currently makes a internal o-ring damper and Fluidampr listed subaru in some of their adds but not on their website. And for some reason, wrx's like to spin rod bearings.
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