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Old 01-27-2004, 02:37 AM   #1
supermoose
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Default EJ25 dohc heads+ phase 2 block = what compresson ratio?

hey, pondering a cheap way to gain compression to bump some more NA power,

add my DOHC EJ25 heads to the 10:1 phase 2 block and use the thin head gaset from the phase 2. anyone have any ideas of waht the compression ratio would be?

there are numbers here, but i cant do the math (hate math)

link:
http://wac.addr.com/auto/obs/turbo/ejcalcs.html

h
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Old 01-28-2004, 04:58 PM   #2
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bmp!
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Old 01-29-2004, 11:59 AM   #3
yebokmj
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Default talked to wac

I have this setup unfortunately. And using the DOHC gasket wac guestimated my compression ratio to be 10.3-10.5 with out being there and doing his own messurements.
Joshua
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Old 01-29-2004, 03:07 PM   #4
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hmm. do you like it or not? any idea what compression ratio with DOHC gasket / SOHC gasket?

h
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Old 01-29-2004, 03:20 PM   #5
WRX34
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EJ20 info for myself

http://www.offroadvw.net/bajawes/V6_baja/compare.html

And for Comp. Calc:

http://www.race-cars.net/calculators...alculator.html

Just some dumb links, you need to know dome/dish etc. and that requires searching and <I'm lazy.

I think by changing by only a +10mm in gasket wouldn't increase it that significantly. (maybe + .1-.2 tops) But I'm trying to find out about swaping heads for most EJ's and trying to find a nice NA or nice turbo compression that would work "in theory" in my 1.8 > 2.0 thread. Maybe do some nice Eagle rods or similar and change ur piston to domed +10-15 if u wanna build it up that much. I'm not sure how much the block can hold tho.

EDIT: Just looked at that link up top...AWESOME info.
http://wac.addr.com/auto/obs/turbo/ejcalcs.html

Thanks for posting that!

WRX34

Last edited by WRX34; 01-29-2004 at 03:31 PM.
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Old 01-29-2004, 05:24 PM   #6
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Default Valve clearance?

I wonder if there would be valve clearance issues with the SOHC gasket? Anyways as to the compression with a SOHC all I can guess is hight than with the DOHC maybe as much as 10.7?
Joshua
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Old 01-30-2004, 11:31 AM   #7
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Old 01-31-2004, 03:52 AM   #8
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12:1 is kinda crazy, not completely understanding how the differance between 2 phase 2 ej25 sohc bottom ends would be so differnt

could you explain? (i dont know much engine math)

h
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Old 02-02-2004, 01:10 PM   #9
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You really have to cc everything out and know how much the piston is above, below or flush with the deck at TDC to get exact static CR. The numbers I got are calculated from the charts on Wayne's site.
This is for 98 DOHC heads with SOHC gasket on the 1999 and 2000 block.
To get CR you add the swept volume (616) to the combustion chamber volume (1999 = 65.5, 2000 = 56.5 ) and divide that by the combustion chamber volume.
To get combustion chamber volume you add the quench, head and piston volumes together.

1999 would be 616+65.5 =681.5/65.5=10.40:1 CR.

2000 " " 616+56.5 =672.5/56.5= 11.9:1 CR.

The differance between the two years is 99 has a piston volume of 15cc's and 2000's is 6cc's. Thats 9cc's less in the 2000's combustion chamber volume and that's why the 2000's CR would be higher.
I added the piston volume to the swept volume in my earlier post and thats why the CR was even higher.
Hope that helps.

Cheers,Tod
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Old 02-02-2004, 01:14 PM   #10
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Default 2000 and DOHC gasket?

What do you get for the 2000 block with DOHC heads Phase 1 and a DOHC gasket? Just would like another person's math on this one to confirm what I was told.
Joshua
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Old 02-02-2004, 04:00 PM   #11
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Default Joshua

From his charts I get

616+63.8=679.8/63.8 = 10.65:1 CR.
Thats if your pistons were flush with the deck at TDC and thats not adding piston volume to the swept volume. Then it would be
10.75:1 CR.


-Tod
Edit for spelling
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Old 02-02-2004, 11:18 PM   #12
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thanks man. ir hate maff.

anyone know if the valves will clear if i run the SOHC gasket??

h
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Old 02-02-2004, 11:33 PM   #13
yebokmj
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Thanks Tod, I wonder how long this engine is going to last under boost? It's been fine for awhile but I am curious if the warm weather will be the end of it.
Joshua
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Old 02-03-2004, 02:12 PM   #14
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Your guys are welcome.
Can't help you on the longevity on your motor question.You've heard it all before I'm sure.

-Tod
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Old 03-31-2005, 02:25 PM   #15
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I'm getting an engine rebuilt in my 97 Outback with a new short block. Subaru wont sell anyone a refurbished phase I block so I got a brand new phase II block. My heads are being milles but I do not know how much. They did mention that they had to shave the valve stems a bit so they'll clear. They're using factory recommended head gaskets. I'm trying to find out what the compression would be if the milling is not accounted for. From your calculations it seems that it would be 11.9:1 (*joy*). Did I misread your calculations?
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Old 03-31-2005, 03:18 PM   #16
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You didn't misread the calcs. It really will be that high......higher with the milled heads. The tipping of the valvestems is to preserve the height in the head for the shims. Unless the person doing it is very-very meticulous....you'll still be searching around for shims to get the clearances right. Ask me how I know.......


Jay Storm
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