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05-03-2004, 04:44 PM | #1 |
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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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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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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 |
05-03-2004, 09:02 PM | #4 |
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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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05-03-2004, 11:26 PM | #5 | |
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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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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. |
05-04-2004, 12:07 PM | #8 |
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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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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 |
05-04-2004, 01:08 PM | #10 | |
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Quote:
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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05-05-2004, 12:51 AM | #11 |
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thanks for all the info
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05-05-2004, 10:51 AM | #12 |
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the thought of putting thinner head gaskets is retarded
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05-05-2004, 12:12 PM | #13 |
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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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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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05-05-2004, 01:40 PM | #15 | |
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Quote:
Randy |
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05-05-2004, 03:15 PM | #16 |
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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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05-05-2004, 05:00 PM | #17 |
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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 |
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 |
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 |
05-06-2004, 12:20 AM | #20 |
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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! |
05-06-2004, 02:39 AM | #21 |
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05-06-2004, 11:18 AM | #22 |
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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 |
05-06-2004, 12:58 PM | #23 | |
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05-06-2004, 03:54 PM | #24 | |
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Quote:
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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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 don’t 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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