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Old 07-28-2008, 03:11 PM   #1
tooocool49723
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Join Date: Jul 2004
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Location: Belleville, MI
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3.3 I <3/h8 my GF3
1.8-2.5-2.2-2.5-2.2-3.3

Default c/r question

Ok, so i'm going to be putting my RS heads on my EJ22 and need to figure out what my CR is gonna be. Stock on the ej22 is something like 9.6, however I know the RS heads have more volume than the single port ej22's. I'll be turboing it, but need to know where i'm starting out at (and also need to decide on thick or thin headgasket). I'm hoping to get around 8.7, but I need to know what it'll be. I've tried all the compression calculators and i've gotten everywhere from 7.7 to 11.

anyone help me?!?!!

'97 EJ22 block, '99 RS heads, can get numbers from here:
http://wac.addr.com/auto/obs/turbo/ejcalcs.html
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Old 08-06-2008, 01:35 PM   #2
tooocool49723
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Default

bump?

I just calculated that at 553cc/cyl at 9.6:1 compression (stock) I should have 57.6cc's of volume at TDC, add 9cc's for the increase in volume from teh phase 2 heads and I get 562cc's of cylinder volume and 66.6cc's at TDC, which gives me 8.43:1 compression.

Is this right or am I totally off base? I know that a 2.2T block with this setup has about 7.7:1.

Please someone, teach me how to do this math! I'm not asking for an answer just point me in the direction of the right formula!

Also, just for gits and shiggles, would a 8.4:1 compression motor be daily driveable in n/a form? albeit with no powa. Debating on doing my build in 2 stages, head swap first then turbo second. or just all in one fell swoop.
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Old 08-06-2008, 10:28 PM   #3
PhilSine
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98 OBS-T, 91 Legacy SS

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How much boost do you plan on running?
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Old 08-07-2008, 01:05 PM   #4
tooocool49723
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Probably start out at about 7psi, then once i get over that learning experience turn it up.
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Old 08-07-2008, 11:01 PM   #5
PhilSine
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98 OBS-T, 91 Legacy SS

Default

From what I understand, the stock internals of your (and mine for that matter) can only effectively handle about 11 psi. That is based upon the notion that you'd be running the stock 9.7:1 CR. I'm not trying to say that more isn't possible I'm only saying that based upon my research those that have attempted more boost have experienced failures.

So don't plan on turning it up too much.
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Old 08-08-2008, 04:44 AM   #6
tooocool49723
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Default

I fully understand that, and whenever I do eventually blow up the 2.2 block, i'll probably buy a STi shortblock to replace it with the turbo setup that i'm putting on now.

But that still doesn't help in my problem of what the actual compression ratio will be. I know it'll be lower than the 9.7:1, just want to know how much lower. My calculation of 8.4 is more of a wild ass guess than anything.
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