Boring and Stroking - Page 2 - Subaru WRX Forum
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#16 Old 04-06-2011, 11:02 PM
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I always though that stroked motors would rev slower, read: lower redline anyway. I get that it gets programmed for it, but wouldn't you want to lower the rev limiter for safety's sake? You're starting to get into the realm of, "Yeah, it's possible, but why would you do that?" If you're dumping that amount of money into it, you could start off with an STi motor (which has a semi-closed deck already) and build it up, like Chris is doing. You're already increasing from the 2.0 to 2.5, and you're really accomplishing much more by getting a setup designed to work together. You can get blocks that are pre-built for $2600, including forged pistons already installed. That's for the EJ257 STi motor. I know because I looked into it for my build. If you're really going crazy, look into blocks like Cosworth builds but know you're paying a little for the Cosworth name.

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#17 Old 04-07-2011, 08:13 AM
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The rev limit all depends on the components used, and your general theory that longer stroke=lower redline is true if stroke is the only thing changed.

And the reason I suggested sleeves is they are almost as cheap as an STi short block but infinitely stronger at least in my neck of the woods, getting a set of sleeves installed will run about $1000 including parts vs a used short block $600-700 that you still need to send to the machine shop and get cleaned up for another $200-300 plus sleeves allow you to have what ever bore you want

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#18 Old 04-07-2011, 09:04 AM
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My used SB was $300

All in the short block cost me $580 to purchase and get worked on. Not trying to argue but deals are out there. Now, if you can pick up a junk short block for free and sleeve it... It'll be cheaper but in my research Darton charges about $1,200 to sleeve the block, and then you still need to get it machined to fit your pistons.

Add that to the fact that I've seen a couple 100mm EJ25's blow/melt pistons and still have intact cylinder liners, I'm not worried about going to 100mm on my block.

To discuss rev limiter, generally a longer stroke, resulting in a lower rod/stroke ratio doesn't like to rev has high. That and they really don't need to as a stroker kit is great for making low to mid end power.

Other things to consider for your rev limiter is really just your overall rod/stroke ratio (higher than 1.65 is better, stock EJ25 is about 1.66 or so), main/rod bearing clearances, valve springs (need better springs to keep the valves from floating at high rpm's). A bit larger bearing clearance will give you a bit more margin of safety to spin the crank higher, but you also need to allow more oiling to keep up with the extra volume needed to fill those larger clearances. Going with larger clearances and not upgrading your oiling system is a bad idea.

Check out a 2.35L longrod destroked 2.5... They're really gaining popularity for their ability to have the piss revved out of them and make big power on big turbo's that like the high rpm's. They're basically a 2.5L case, 2.0L crank, and longer rods to make up for the reduction in stroke.

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#19 Old 04-07-2011, 10:23 AM
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Chris you've basically described the motor in my car now, except I'm using a custom bore I'm slightly smaller pistons total displacement is 2.25L Rev limit is 8500 and the turbo is still pulling all the way to redline

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#20 Old 05-16-2011, 08:01 AM
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I would like to ask something here, the only engine I ever contemplated stroking was a Mk2 Escort, when I blew the 1600 & was given a 1300 & really wanted a 1600, but they are different hights so this wouldn't have worked... but will it with a Subaru?
No matter where I look I cant find anything to tell me... but would the little EJ15 happen to be the same width as an EJ20? & can I put an EJ20 crank & rods into the 1500 to make it 1700cc? (or even 1800cc with 1600 pistons)
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#21 Old 05-16-2011, 08:27 AM
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no, the EJ15 is a different case

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#22 Old 06-21-2011, 08:40 AM
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Check out a 2.35L longrod destroked 2.5... They're really gaining popularity for their ability to have the piss revved out of them and make big power on big turbo's that like the high rpm's. They're basically a 2.5L case, 2.0L crank, and longer rods to make up for the reduction in stroke.
That would be the route I went. Although I went with Stock STi rods and wound up with a 7.2:1 comp ratio. Sucks off boost sometimes, but it has provided alot of smiles...

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#23 Old 06-21-2011, 09:18 AM
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what pistons are you using? I've decided that if/when my current 2.2L stroker fails I'm likely to sleeve my current block and build a 2.35 but I could not deal with that low of a compression ratio

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#24 Old 06-21-2011, 09:41 AM
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what pistons are you using? I've decided that if/when my current 2.2L stroker fails I'm likely to sleeve my current block and build a 2.35 but I could not deal with that low of a compression ratio
Wossner pistons (100mm). My old 91 DSM had 7.5:1 compression, so it's not to bad, but where I live I drive 3 miles to work and back and boat loads of stop lights and that's the only bad thing. I basically bought a used STi block had it machined and went from there. Although I did run into a few issues, like which oil pump to go with since i'm running non avcs heads but revving to 8700. It has been fun though. When I blew a hole through the stock 2.0 piston I had thought of going with a 2.2L rebuild with lower compression, but then I saw the idea for this motor and went with it.

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#25 Old 06-21-2011, 09:55 AM
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Wossner, NICE! my old man runs those in his Porsche, do you happen to know the compression height on them? If I do a 2.35 I want to run stock length rods to keep the ability to rev but I can't seem to find any setups similar to what I want to build in the future

I had the same oil pump debate when I first built the motor, I wanted to be able to spin up to 9K with EJ205 heads I ended up consulting Lim Tan who recommended me to go with the Cosworth pump so I feel safe with my 8500 limit

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#26 Old 06-21-2011, 10:44 AM
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Wossner, NICE! my old man runs those in his Porsche, do you happen to know the compression height on them? If I do a 2.35 I want to run stock length rods to keep the ability to rev but I can't seem to find any setups similar to what I want to build in the future

I had the same oil pump debate when I first built the motor, I wanted to be able to spin up to 9K with EJ205 heads I ended up consulting Lim Tan who recommended me to go with the Cosworth pump so I feel safe with my 8500 limit
Porsche forums were how I found out about them....haha

30.7 comp height I believe I'd have to dig up the spec sheet. On a stock STi 100mm bore they are suppose to be 8.6:1 but with the piston being 2mm farther down the bore it drops it alot. What brought it up was the CC of the WRX heads. I HIGHLY, HIGHLY recommend going with a longer rod to make up the compression. You could still get the high revs if it's balanced properly. I've followed a few threads about these motors and that seems to be the overall consensus. Again when I did mine only a few people had build them, so we were bounce ideas off each other...

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#27 Old 06-21-2011, 12:06 PM
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like I said I'm only in the preliminary stages of planing this monster out, just curious why your recommending the longer rods over a slightly taller piston?

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#28 Old 06-21-2011, 12:51 PM
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Higher rod/stroke ratio = more rev happy. More time to dwell at T/BDC, less sidewall loading, etc.

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#29 Old 06-21-2011, 01:39 PM
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like I said I'm only in the preliminary stages of planing this monster out, just curious why your recommending the longer rods over a slightly taller piston?
Don't you want to tell everyone you have a long rod????
In all seriousness this little page will explain alot. Granted it's based on V8 motors, but it gives you the general idea. Lots of math and good stuff like that.
Connecting Rod vs. Stroke Analysis: panic Tech Paper No. 1

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#30 Old 06-22-2011, 06:00 AM
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I always thought a longer rod was asking for problems in any setup (high reving).

Nice to know.

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