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Old 05-03-2004, 04:44 PM   #1
phunkeeHomosapien
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Default Good Idea?

I am having the heads off my 98 2.5 redone and was wondering if there are any possible consequences to having my heads slightly shaved down for higher compression. If you have any suggestions or info on the topic I would greatly appreciate it.
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Old 05-03-2004, 07:32 PM   #2
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it would change the flow characteristics of the cumbustion chamber and make the mixture more turbulent. if you want higher compression, that's not the way to do it.
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Old 05-03-2004, 08:55 PM   #3
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Get them ported if you have the coin to do so, now is the best time to do it!
Dan
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Old 05-03-2004, 09:02 PM   #4
Tim Sanderson
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How much are you thinking about "shaving" off? It's not a bad idea to have a couple thousandths removed to insure a straight, clean mating surface, but enough to increase the c.r. will probably cause problems as handsdown has stated. Valve to piston interference to name one possibility.
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Old 05-03-2004, 11:26 PM   #5
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Quote:
Originally posted by Tim Sanderson
How much are you thinking about "shaving" off? It's not a bad idea to have a couple thousandths removed to insure a straight, clean mating surface, but enough to increase the c.r. will probably cause problems as handsdown has stated. Valve to piston interference to name one possibility.
Oh ****, that's right! Our engines are interference powerplants which means that if the clearance is not correct the valves can meet up with the cylinders and really bad things happen from there.
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Old 05-03-2004, 11:46 PM   #6
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also, you'd lose precious displacement, which is the only thing we do have, sadly.
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Old 05-04-2004, 01:52 AM   #7
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my friend mike is the one that started this thread and im the one who gave him the idea....


its just that i know that people have done this on civics and SR20's and sutch, and i was just wondering if you could due the same to the EJ25....also if you think of if, people put thicker head gaskets to lower their CR, so this is just the oposite.
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Old 05-04-2004, 12:07 PM   #8
phunkeeHomosapien
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yeah i will probably get the heads polished and leave it at that, the engine has quite a few miles on it any ways
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Old 05-04-2004, 12:57 PM   #9
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After consulting my service manuals. There is a .1 mm grinding limit. That is the equivalent of 4 thousandths. That is the most you should have removed. That will net a miniscule compression increase.

Good luck
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Old 05-04-2004, 01:08 PM   #10
GuyLR
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Quote:
Originally posted by Handsdown
also, you'd lose precious displacement, which is the only thing we do have, sadly.
No displacement is lost by shaving the head. Displacement is determined by the volume of the cylinder swept by the piston and doesn't include the combustion chamber.

If the engine had any history of head gasket leaks or the head surfaces aren't flat I'd take that 0.1mm off.
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Old 05-05-2004, 12:51 AM   #11
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thanks for all the info
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Old 05-05-2004, 10:51 AM   #12
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the thought of putting thinner head gaskets is retarded
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Old 05-05-2004, 12:12 PM   #13
phunkeeHomosapien
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people put thinner head gaskets on SR20's, B series engines, MR2's, so pretty much any car, and its not like i am running boost or any thing so it shouldnt be a big deal.
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Old 05-05-2004, 12:12 PM   #14
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i am just going to run the oem gasket any ways.
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Old 05-05-2004, 01:40 PM   #15
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Quote:
Originally posted by ehlpitel
the thought of putting thinner head gaskets is retarded
Why??

Randy
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Old 05-05-2004, 03:15 PM   #16
greg donovan
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while i dont feel as harshly as elphitel. i think he means because the thinner sohc gasket is not as robust as the thicker dohc one. it could raise the CR to the point of detonation too.
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Old 05-05-2004, 05:00 PM   #17
Randoramma
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just a headgasket? And I am pretty NOOB to the subaru or any H motor, but I have been working ot toyotas for years, and alot of them have metak headgaskets that are alot more robust than the normal ones. I assume they make them for the soob's as well, correct?

Randy
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Old 05-05-2004, 05:21 PM   #18
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randy got my back

ive heard of MANY people put thiner head gaskets on Turbo MR2's, my buddy was going to do it but didnt have the extra $$ for the HKS gasket so he just got OEM....

im the one that gave phunky... the idea so thats why im puting in my .o2

so i thought becoue you could do that to other engines i didnt see why you coundnt do it to a subaru, so that all
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Old 05-05-2004, 06:03 PM   #19
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Sure, and I'm not familiar with the turbo setup, but people do it on NA's all the time. It doesnt affect it all that much.

Randy
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Old 05-06-2004, 12:20 AM   #20
greg donovan
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here is a good site for subaru engine specs

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

the subaru headgaskets are metal.

my tech. and i figure subaru put the thinner gasket on the phaseII to compesate for switching to sohc by upping the CR a little.

he says the thin ones are terrible compared to the old thick ones.

using numbers from the ejcalcs site and here:

http://forums.nasioc.com/forums/show.../t-40362.html:

and plugging them into here:

http://www.kb-silvolite.com/calc.php...1441a39409fc71

i got a cr for my franken subie project idea of 11.64:1 with the thick(dohc) gasket and a cr of 14.32:1 w/the thin(sohc) one.

here are the numbers for ej25 converted to inches for you so you can enter them into the site quicker. get the head volumes from ejcalcs.

gasket thickness(thin) 0.0228346"
gasket thickness(thick) 0.0598425"
gasket bore 3.9173"
cyl bore 3.9173"
stroke 3.1102"
rodlength 5.1850"
intake closing point deg ABDC 52 deg.(this is for ej22 heads)
got pointed to alot of this stuff by my guys at the legacy central bbs.

so the head gasket makes a big difference on subarus.

greg
go old school scoobys!
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Old 05-06-2004, 02:39 AM   #21
joefocker20
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Old 05-06-2004, 11:18 AM   #22
Randoramma
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Ok, but aren't you going from a stock gasket thickess of 1.52mm all the way down to .58mm?? Thats very thin. I believe the stock 4age gasket was 1.6 mm and we never went even to the 8mm ones.. Obviously there is a limit between performance and practicality. Now I bet if you went to something like 1mm or even .8mm they might not be "terrible"?

Randy
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Old 05-06-2004, 12:58 PM   #23
phunkeeHomosapien
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Quote:
Originally posted by greg donovan
here is a good site for subaru engine specs

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

the subaru headgaskets are metal.

my tech. and i figure subaru put the thinner gasket on the phaseII to compesate for switching to sohc by upping the CR a little.

he says the thin ones are terrible compared to the old thick ones.

using numbers from the ejcalcs site and here:

http://forums.nasioc.com/forums/show.../t-40362.html:

and plugging them into here:

http://www.kb-silvolite.com/calc.php...1441a39409fc71

i got a cr for my franken subie project idea of 11.64:1 with the thick(dohc) gasket and a cr of 14.32:1 w/the thin(sohc) one.

here are the numbers for ej25 converted to inches for you so you can enter them into the site quicker. get the head volumes from ejcalcs.

gasket thickness(thin) 0.0228346"
gasket thickness(thick) 0.0598425"
gasket bore 3.9173"
cyl bore 3.9173"
stroke 3.1102"
rodlength 5.1850"
intake closing point deg ABDC 52 deg.(this is for ej22 heads)
got pointed to alot of this stuff by my guys at the legacy central bbs.

so the head gasket makes a big difference on subarus.

greg
go old school scoobys!
you kick @ss, thats exactly what i was looking for....im amazed to how helpful that was....
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Old 05-06-2004, 03:54 PM   #24
snowman4us
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Quote:
Originally posted by Randoramma
Ok, but aren't you going from a stock gasket thickess of 1.52mm all the way down to .58mm?? Thats very thin. I believe the stock 4age gasket was 1.6 mm and we never went even to the 8mm ones.. Obviously there is a limit between performance and practicality. Now I bet if you went to something like 1mm or even .8mm they might not be "terrible"?

Randy
if you whould actualy payed attention the thiknes is .152 and not 1.52 whitch is aproximatly 10X thicker ...and the thiner one is .058 and not .58

and the CR goes from 9.4:1(stock thick head gasket from a 98RS DOHC) to a 10.5:1(with a stock 99RS SOHC head gasket). so its only 1.1 higher, whitch isnt a big enoug(sp?) diff. to couse problems.
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Old 05-06-2004, 04:59 PM   #25
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Sorry mate, I guess my SAE -- Metric converter wasnt paying attention when I entered greg's numbers...so it gave me the numbers I posted.. Thanks for taking the time to clear that up!! However, I think your right the decimal was off by a place... and perhaps if you bump up the octane by a grade what ever probs that might occur (I donít think anybody has given a specific example yet, guessing detonation?) will go away.... I cant imagine these engines not taking 10.1 compression in stock internals..if thats the case, I'll be looking for another car stat!!! Thanks for the info guys!!

Randy


You might check out that converter to see if its giving you what it gave me...it might be faulty!!

https://www.cstsales.com/Main/converter.htm
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