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Old 03-26-2009, 10:42 AM   #1
patrickscycleshop
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Default ?thickest head gasket on 2.5na dohc engine?

i am redoing my forester 98 ej25 dohc engine, the heads need to be milled, i already had 210 psi on all 4 cylinders prior to dissassembly before head gaskets leaked. heads have obviously been milled before. i had to run 93 octane fuel to keep it from sparkknocking, want to ressemble with thickest head gaskets to keep compression ratio down as low as possible without replacing heads, previously had aftermarket garbage gaskets which failed, i only want to use oem parts.thanks for your advice in advance.
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Old 03-26-2009, 11:13 AM   #2
Matt Monson
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The warpage limit on those heads is 0.05mm and the grinding limit is 0.3mm. If they've been milled once already doing it again will likely put them beyond spec. You're probably going to need to find another set of heads.
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Old 03-26-2009, 11:21 AM   #3
patrickscycleshop
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Default head ccs?

does anyone know the head ccs (combustion chamber cc's of the head) for the ej25 na dohc engine? for an original unmilled set of heads?
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Old 03-26-2009, 11:43 AM   #4
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46cc.

Last edited by Matt Monson; 03-26-2009 at 11:52 AM.
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Old 03-26-2009, 11:44 AM   #5
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mm is not a fluid measurement, did you mean ml?
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Old 03-26-2009, 11:52 AM   #6
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Old 03-26-2009, 11:57 AM   #7
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great that is very helpful, now i can cc my heads and the deck height and the thickness of the head gasket and arrive at what the compression ratio should be, do you know the various head gasket thicknesses?
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Old 03-26-2009, 12:32 PM   #8
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ive got 44 cc on mine, now ive got to figure out the exact stroke and fluid ccs at tdc with my pistons and ill know what ill end up with.then i know how much i can mill off the heads. from what i have researched with high comp pistons 11.1:1 is safe with 93 octane, i dont know where mine is till i compute the figs
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Old 03-26-2009, 03:35 PM   #9
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The thing you need to be concerned with it's the compression ratio but warped and repeatedly having the head gaskets fail. If the head gets milled to thin you'll be lucky if you get 20k mi out of it regardless of headh gasket thickness.

That said, you will need to get a custom head gasket made if you want to go thicker. The 1997-1999 DOHC Ej25d engines got the thickest head gaskets Subaru has ever made. All other variants of head Ej25's had thinner, not thicker head gaskets.
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Old 03-26-2009, 03:40 PM   #10
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do you know wha the thickness of that head gasket is supposed to be? the gasket i took out of the engine was not a subaru oem gasket, i think the guy told Eristic brand, it was deteriorated and falling apart, I believe that is the reason it failed in the first place.the best measurement i can get off them is 1.26 mm, that obviously compressed being used.
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Old 03-26-2009, 04:13 PM   #11
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That's close. 1.52 is stock. That's too thick to be a phase II gasket. Those are only 0.58.
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Old 03-26-2009, 04:23 PM   #12
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thats cool, do you know of compression ratio calculator thatworks with the following sites numbers? http://www.wac.addr.com/auto/obs/turbo/ejcalcs.html
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Old 03-26-2009, 06:22 PM   #13
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came out consistent with the piston deck hieght set at 0 with what the compression ratios other people have got. based on the info from ejcalcs website info.
this appears to be a good compression ratio calculator

http://www.rbracing-rsr.com/compstaticcalc.html

Last edited by patrickscycleshop; 03-26-2009 at 06:35 PM. Reason: added wording to increase search success
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Old 03-26-2009, 06:33 PM   #14
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i should have had 10.0:1 the way my engine was assembled, i could take the head ccs down as far as 37 ccs that would yield an 11.1:1, but I dont think that much would have to be taken off the heads to level them, only way to know is to have them mill them and cc them
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Old 03-26-2009, 07:26 PM   #15
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Check TWE's compression ratio calculator, which is on my website here. Some of the numbers are a bit different than the ones on wac's website, and it's got more up-to-date info.

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