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Old 10-31-2010, 06:28 PM   #76
07ImprezaMB
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Would a stock ej257 match fine with my heads? or do i HAVE to get custom pistons made?
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Old 10-31-2010, 07:10 PM   #77
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the valve reliefs are in the wrong areas, there are no quench pads and I don't know your combustion chamber volume.

Without getting another one of those heads here to measure the volume and verify no piston to valve contact I cannot answer that question.
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Old 03-01-2011, 10:45 AM   #78
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bump from the dead
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Old 08-25-2011, 04:24 PM   #79
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I have a 2000 RS and I'm contemplating the idea of using the STI block with forged internals and my stock heads with upgraded valves and valve train. Today I was told that that was a very bad idea because the SOHC heads don't like boost and it wont be reliable. That I was better of doing a swap which i rather not because of all the wiring hassle. I will probably use the Hydra for EM and hope to get around 300 hp and tq. From what I read here it seems like it will work now what has me worried is the valve relief issue of the pistons. I know the pistons and rods are not interchangeable. I was planing to buy 8.0:1 STI pistons with STI forged rods. Will that work or will I need custom pistons to match the valve relief on the head plus corresponding rods?
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Old 10-25-2011, 07:35 PM   #80
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Quote:
Originally Posted by kaos200
making this for all the newbs

Specs
EJ257 with SOHC heads approx 8.4:1 (since the sohc has 3cc more volume then the wrx heads according to Cobb)
EJ257 with WRX heads approx 8.6:1
EJ257 with STi heads approx 8.2:1

Good to atleast 7500rpm (from personal experience, others may go higher, im not that crazy)
Are holding up to 20+psi boost, and 450whp so far without much trouble (again, its all in the tuning/setup)

If installing into RS with sohc. parts needed are...
- STi headgaskets

-WRX upper coolant pipe... requires the following
-- coolant line from pepboys/kragen to go to heater core, stock prerouted piece will not work
-- you need to grind some metal off the passenger side cylinder head near where the upper radiator hose attaches to the upper coolant pipe. A die grinder makes quick work of this.
-- you need to lengthen the wires for the coolant temp sensor, since it sits in a different location.
-- you need to do the coolant through throttle body bypass mod, AND remove the little piece of metal that sticks into the throttle body that the coolant goes through, or else it will hit the new upper coolant pipe where it meets the heater core hose. (yank out or cut off, your choice)

OR, use the stock upper coolant pipe, but you need to measure where to cut out a chunk of it since the block has that extra breather, then weld the hole in the pipe shut.

If installing with dohc, you can use either upper coolant pipe, and if using the one meant for the wrx, you do not need to grind the heads, but the other mods must be done. INCLUDING....

-DOHC Oil dipstick tube, it mounts to the head differently.

-You still need the STi head gaskets.

If using wrx heads, you can use the stock RS intake manifold, and everything else but you must drill out the manifold bolt holes, and shave some of the plastic on the driver's side valve breather piece (hard to describe, black plastic piece that attaches to top of valve cover, well, guess its not THAT hard to describe)

If using STi heads, you MUST use the sti/wrx intake manifold, and rails etc. I had an adaptor made to use my stock RS throttle body, but that was such a pita
So using STi heads, pretty much means you've gone and changed the entire motor setup, and you're going to probably do an ecu swap as well.

If im missing anything just post it and Ill add it so people doing a search can just find it all here.
So. Are you saying that if you use wrx heads in an rs that you do not have to do an eclub/harness swap? Just em?
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Old 10-25-2011, 07:36 PM   #81
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Ecu not eclub. Lol. Damn android spell check.
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Old 10-25-2011, 07:43 PM   #82
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Quote:
Originally Posted by tplumsti View Post
So. Are you saying that if you use wrx heads in an rs that you do not have to do an ecu/harness swap? Just em?
Holy old thread. I should probably update my first post.

How are you surmising that?
I'm confused by your post. You're asking if you do NOT have to do an ECU swap, but just an EM (engine management) change? Sorry I'm just confused by your wording here.

In any case. No, if you switch from SOHC to DOHC, you must change the ecu somehow. Either do a wiring swap and go OEM or use a standalone system.
That being said, I had moved away from recommending piggybacks and standalones years ago. I've done so many wiring mergers for people now it's not even funny. Another benefit of that is that for those in smog strict states (like good ol' CA) the swap would be legal.

EVERYONE NOTICE THE ORIGINAL POST WAS FROM 2004!
I INTENDED IT FOR GC MODEL 2.5RS, NOT NEWER MODELS.

Last edited by kaos200; 10-25-2011 at 07:56 PM.
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Old 10-25-2011, 08:49 PM   #83
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Yes. That's what I was asking. I have a 99rs and the way I was reading the original post was basically, unless you are using sti heads you could get by without rewiring. I don't really want to go the full swap route .... wiring harness especially. I do have an sti block though that I could use. I will do some more research as far as using the stock rs heads /sti block then. Ty
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Old 10-25-2011, 09:04 PM   #84
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Quote:
Originally Posted by tplumsti View Post
Yes. That's what I was asking. I have a 99rs and the way I was reading the original post was basically, unless you are using sti heads you could get by without rewiring. I don't really want to go the full swap route .... wiring harness especially. I do have an sti block though that I could use. I will do some more research as far as using the stock rs heads /sti block then. Ty
I see. Well, I'd still recommend doing atleast a full engine swap. You don't have to wire in the DCCD setup if you don't want to (standalone DCCD controllers exist, and those are actually quite good).
Up to you! If you ever need help with the merger let me know.
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Old 10-25-2011, 09:07 PM   #85
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Ty sir!
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Old 11-15-2011, 06:36 PM   #86
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Is there a way to calculate CR? I'm dropping a built 257 block into my 04 RS this weekend with manley 8.5:1 pistons, OEM headgasket and the SOHC 251 heads.
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Old 11-15-2011, 06:44 PM   #87
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Quote:
Originally Posted by Burks569 View Post
Is there a way to calculate CR? I'm dropping a built 257 block into my 04 RS this weekend with manley 8.5:1 pistons, OEM headgasket and the SOHC 251 heads.


9:1 ish.
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Old 11-22-2012, 04:19 AM   #88
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Old thread but it's full of knowledgeable people. I'm in the process of doing small boost on my stock SOHC 2.5rs. 10.1 Compression, only planning on running 5-8psi until I find a suitable STI that been wrecked for a full drivetrain donor. I'm going through and doing the headgaskets along with just about every other seal and wear item short of tearing into the short block. Just have a couple questions as the contributors to this thread seem to be well versed.

What are my options for Valve Springs? What would you recommend given my high compression / low boost application?

I'm using a TD04 turbo, at least initially. I know it was said that this was not the best turbo for the job earlier in the thread. Is there any resources I can use to learn more about this? Is this anything I can do in the fabrication of my up and down pipes, or the rest of the installation to make reduce the ill effects of using this turbo in my High Compression stock motor?

Thank you in advance, and I apologize to those of you who don't like old threads being brought up.
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Old 11-30-2012, 02:33 AM   #89
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For the amount of boost you are looking at running, you can leave your stock springs. I run almost 3 times the amount of boost and haven't had any issues.

I am sure you can find somebody selling UP and DP from Turbo Kits. Otherwise you need to look into getting a Turbo X-member and getting WRX pipes.

When getting into a project like this my recommendation is: Do it right the first time. If you cheap out on certain steps, you will end up paying for it afterwards. Buy quality and get the right parts from the beginning. A lot of custom fabrication can end up in headaches in the end.

When you add everything up, it may be cheaper to just buy a car that has already been done (granted you won't have the learning experience, but it will be cheaper)...

Hope this helps
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Old 11-30-2012, 09:38 AM   #90
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Quote:
Originally Posted by maxiav View Post
For the amount of boost you are looking at running, you can leave your stock springs. I run almost 3 times the amount of boost and haven't had any issues.



Hope this helps
That's what you think.

when you take the engine apart you'll find pits in the tip of your valve stems. if you run it you long you'll find your valve lash increases over time and your heads get noisier and noisier until you have a failure.
10 is enough to minutely float the valve and start pitting.
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Old 11-30-2012, 10:38 PM   #91
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raptorsc has been running supercharged kits with 6-11 psi on dozens of cars/10's of thousands of kilometres for years without issues. but psi isn't psi...

Last edited by vicious_fishes; 12-01-2012 at 07:11 AM.
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Old 12-01-2012, 09:46 AM   #92
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Actually it isn't.
Turbochargers create exhaust back pressure in addition to manifold pressure, where super chargers only create manifold pressure.

Boost on the back side of a valve tries to blow the valve open and/or hold it open. The higher the rpm, the less boost is required. So if you have two owners with ten psi, one might not experience any pitting because he drives the car easier by not red lining the car.
Also, if you have a small turbo that makes ten peak, but tapers toward red line, you're more likely to float exhaust valves due to high exhaust pressure than intake valves because boost is lower as rpm increases.


You guys can argue all you want and point to other people's experience if you want. The fact remains that you haven't taken apart as many turbocharged rs's as I have. I had three of my own engines that I took apart, my business partner had his that I worked on, at least five customers' engines and two other friends. All were a little different and all showed a similar trend if the boost was higher. Only two had actual failures, but many of them showed the damage presented by valve float or excessive lash.

I'm trying to express a word of caution for a user and potentially help keep him from a premature failure.
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Old 12-01-2012, 04:24 PM   #93
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Quote:
Originally Posted by Maxwell Power View Post
Actually it isn't.
Turbochargers create exhaust back pressure in addition to manifold pressure, where super chargers only create manifold pressure.

Boost on the back side of a valve tries to blow the valve open and/or hold it open. The higher the rpm, the less boost is required. So if you have two owners with ten psi, one might not experience any pitting because he drives the car easier by not red lining the car.
Also, if you have a small turbo that makes ten peak, but tapers toward red line, you're more likely to float exhaust valves due to high exhaust pressure than intake valves because boost is lower as rpm increases.


You guys can argue all you want and point to other people's experience if you want. The fact remains that you haven't taken apart as many turbocharged rs's as I have. I had three of my own engines that I took apart, my business partner had his that I worked on, at least five customers' engines and two other friends. All were a little different and all showed a similar trend if the boost was higher. Only two had actual failures, but many of them showed the damage presented by valve float or excessive lash.

I'm trying to express a word of caution for a user and potentially help keep him from a premature failure.
i actually agreed with you... as i said and you implied, psi isn't psi. especially supercharged vs turbocharged.

i'm well aware of how well you guys know your stuff. in fact im kind of in awe of it
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