Welcome to the North American Subaru Impreza Owners Club Thursday December 25, 2014
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Here you can view your subscribed threads, work with private messages and edit your profile and preferences Home Registration is free! Visit the NASIOC Store NASIOC Rules Search Find other members Frequently Asked Questions Calendar Archive NASIOC Upgrade Garage Logout
Go Back   NASIOC > NASIOC Technical > Normally Aspirated Powertrain

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads.
Reply
 
Thread Tools Display Modes
Old 01-03-2011, 06:55 PM   #1
ditto151
Scooby Newbie
 
Member#: 261850
Join Date: Oct 2010
Chapter/Region: BAIC
Location: Oakland
Vehicle:
1994 RS
Red

Default what is a good head gasket

i want to get a pair of some cosworth head gaskets and i just called to Subaru dealership and the don't even know the millimeter size or bore of any of the head gaskets they carry, and so my question is what millimeter and bore size head gaskets should i get that dose not change the compression ratio
* Registered users of the site do not see these ads.
ditto151 is offline   Reply With Quote
Old 01-04-2011, 12:58 AM   #2
Storm
Scooby Guru
 
Member#: 5218
Join Date: Mar 2001
Chapter/Region: MWSOC
Location: SAUL'S Motorsports
Vehicle:
96L Most Over-
Developed Beater

Default

What motor you running?
Storm is offline   Reply With Quote
Old 01-04-2011, 02:23 AM   #3
williaty
Scooby Guru
 
Member#: 71092
Join Date: Sep 2004
Chapter/Region: MWSOC
Location: Delaware County, Ohio
Vehicle:
2005 2.5RS Wagon
Regal Blue Pearl

Default

Realistically, the stock head gaskets are quite good if you properly prepare the block and heads. You need to be doing something crazy before alternative gaskets pay off. If you're doing it on a basically stock motor "just to be safe", you're barking up the wrong tree.
williaty is offline   Reply With Quote
Old 01-04-2011, 12:18 PM   #4
Samirr76
Scooby Guru
 
Member#: 4835
Join Date: Mar 2001
Chapter/Region: Tri-State
Location: Fl33tw00d, PA
Vehicle:
2003 Baja 5MT
Yellow w/ 220,000 miles

Default

Quote:
Originally Posted by williaty View Post
Realistically, the stock head gaskets are quite good if you properly prepare the block and heads. You need to be doing something crazy before alternative gaskets pay off. If you're doing it on a basically stock motor "just to be safe", you're barking up the wrong tree.
Ditto.
Samirr76 is offline   Reply With Quote
Old 01-06-2011, 01:11 AM   #5
ditto151
Scooby Newbie
 
Member#: 261850
Join Date: Oct 2010
Chapter/Region: BAIC
Location: Oakland
Vehicle:
1994 RS
Red

Default

im trying to get the HG for the 1998 dohc 2.5L that is still all stock the reason because i know these motors have HG problems so i thought of upgrading it and i would never have to worry about them again
ditto151 is offline   Reply With Quote
Old 01-06-2011, 01:14 AM   #6
williaty
Scooby Guru
 
Member#: 71092
Join Date: Sep 2004
Chapter/Region: MWSOC
Location: Delaware County, Ohio
Vehicle:
2005 2.5RS Wagon
Regal Blue Pearl

Default

The problem really isn't the HG itself, it's the design of the entire system.

The best you can do is to make sure the block and heads are flat to within a few tenths and obsessively clean all of the sealing surface. Then follow the factory torquing procedure properly. You'll have to have the engine out to do all of that. That's the best bet you have of putting off the problems as far into the future as possible.
williaty is offline   Reply With Quote
Old 01-06-2011, 03:44 AM   #7
ditto151
Scooby Newbie
 
Member#: 261850
Join Date: Oct 2010
Chapter/Region: BAIC
Location: Oakland
Vehicle:
1994 RS
Red

Default

so i should just get the factory HG even though those are the ones that fail more often i was thinking cosworth because they make those HG to handle alot more pressure
ditto151 is offline   Reply With Quote
Old 01-06-2011, 03:58 AM   #8
williaty
Scooby Guru
 
Member#: 71092
Join Date: Sep 2004
Chapter/Region: MWSOC
Location: Delaware County, Ohio
Vehicle:
2005 2.5RS Wagon
Regal Blue Pearl

Default

Quote:
Originally Posted by ditto151 View Post
so i should just get the factory HG even though those are the ones that fail more often i was thinking cosworth because they make those HG to handle alot more pressure
The BMEP actually doesn't change *that* much at the power levels the 2.5L EJ NA motors can be taken to. It's not as big of a deal as you think.

For the NAs, I'll bet you dollars to donuts that the reason there's slightly less failures with Cometic gaskets isn't the gaskets. It's because they're getting used by guys who are being a hell of a lot more careful with their prep work.


Look, if you take your heads off, peel off the old HG, slap the Cometic on there, and bolt the heads back on, the Cometic IS going to fail. But the guys who are trying to make big power, trying to do it right, and just happen to also be using Cometic gaskets don't just slap things together. They verify the heads and the block are flat to within a couple of ten thousandths of an inch. If it's not, they have a machine shop correct anything that's wrong. They verify that the surface finish (for the Cometics) is between 4 and 40 Ra on all the sealing surfaces. If not, they have a machine shop correct it. The obsessively clean the hell out of everything. They follow the recommended install procedure to the letter using torque wrenches that have been recently calibrated and angle gauges for the yield portion.

If you do just the basics of that: Get a professional to check them for flat (and correct if needed), clean obsessively, and follow the factory procedure to the letter using the correct tools, the factory HG will seal reliably for long periods of time.
williaty is offline   Reply With Quote
Old 01-06-2011, 04:28 AM   #9
AQ Motorsports
Former Vendor
 
Member#: 60836
Join Date: Apr 2004
Chapter/Region: SCIC
Location: Torrance, CA
Vehicle:
2006 Mod Class STI
TIMEATTACK!!

Default

You're fine with using the stock one from the dealership. It is now a MLS gasket like what comes in the wrx/sti and not the crappy one that originally came in the car. 11044AA610 I believe.
AQ Motorsports is offline   Reply With Quote
Old 01-06-2011, 05:01 AM   #10
ditto151
Scooby Newbie
 
Member#: 261850
Join Date: Oct 2010
Chapter/Region: BAIC
Location: Oakland
Vehicle:
1994 RS
Red

Default

thanks
ditto151 is offline   Reply With Quote
Old 01-06-2011, 08:59 PM   #11
PaulieKeyboard
Scooby Newbie
 
Member#: 268990
Join Date: Jan 2011
Default

What's the price one can expect to pay for the pair of headgaskets? Should the valve cover gaskets be changed out at the same time?
PaulieKeyboard is offline   Reply With Quote
Old 01-06-2011, 09:06 PM   #12
derk
Scooby Newbie
 
Member#: 162625
Join Date: Oct 2007
Location: Vancouver BC, Canada
Default

Cometic head gaskets are garbage.

if you're gonna go for a MLS gasket, get a Cosworth one.
derk is online now   Reply With Quote
Old 01-09-2011, 02:31 AM   #13
pho_shizzle
Scooby Specialist
 
Member#: 181064
Join Date: May 2008
Chapter/Region: BAIC
Location: Bay Area
Vehicle:
00' 2.5RS
BRP

Default

Im doing my engine rebuild soon and have included cosworth sti 2.5l head gaskets with a 1.5mm thickness.

The OEM Subaru factory head gaskets should do you just fine because Subaru has updated the parts to a thicker design.

But I decided to go baller with the cosworth head gaskets anyways. If you do decide to get them, make sure you go for the 1.5mm thickness. Stock subaru head gaskets are .054" thickness so the 1.5mm head gaskets are .059" thickness, that should help compensate for the loss of metal that has been shaved off by a machine shop.

Going any thinner than that will increase your compression rate because the thickness is meant for turbo'd engines.

Also the myth about cometic gaskets being ****, well......... everything is **** if you use them incorrectly. As previously stated above, do it right, have your heads measured and shaved for proper and maximum head gasket seal effectiveness.


Best of luck =)
pho_shizzle is online now   Reply With Quote
Old 01-09-2011, 04:02 AM   #14
Disruptin
Scooby Specialist
 
Member#: 184564
Join Date: Jul 2008
Chapter/Region: MAIC
Location: Winchester
Vehicle:
2009 SWP Hatch
Hella Snail'd

Default

used both cosworth and cometic and havent had an issue with either, if your changing head gaskets it has nothing to do with valve cover gaskets unless you take the valve cover off, if thats the case it goes for any gasket if you seperate the parts, change the gaskets why not stick with oem?
Disruptin is offline   Reply With Quote
Old 01-09-2011, 04:03 AM   #15
williaty
Scooby Guru
 
Member#: 71092
Join Date: Sep 2004
Chapter/Region: MWSOC
Location: Delaware County, Ohio
Vehicle:
2005 2.5RS Wagon
Regal Blue Pearl

Default

Most of the EJ engines require the valve covers to be removed to access the head bolts. Just a few of the very older engines had the head bolts outside the valve cover.
williaty is offline   Reply With Quote
Old 01-09-2011, 08:42 PM   #16
ditto151
Scooby Newbie
 
Member#: 261850
Join Date: Oct 2010
Chapter/Region: BAIC
Location: Oakland
Vehicle:
1994 RS
Red

Default

the only reason want after market HG is because i dont really like how subaru changed the coolant flow on the multilayer HG AND I KNOW cosworth is the s***
ditto151 is offline   Reply With Quote
Old 01-09-2011, 09:27 PM   #17
AQ Motorsports
Former Vendor
 
Member#: 60836
Join Date: Apr 2004
Chapter/Region: SCIC
Location: Torrance, CA
Vehicle:
2006 Mod Class STI
TIMEATTACK!!

Default

Quote:
Originally Posted by ditto151 View Post
the only reason want after market HG is because i dont really like how subaru changed the coolant flow on the multilayer HG AND I KNOW cosworth is the s***
what do you mean? coolant passages between the OEM and cosworth are pretty much identical. There are a few different gaskets depending on the year of the car to line up with the passages into the heads.

I'm not saying there's anything wrong with the cosworth gaskets, but we've never had a problem just using stock ones, even on our time attack car.
AQ Motorsports is offline   Reply With Quote
Old 01-09-2011, 09:38 PM   #18
ditto151
Scooby Newbie
 
Member#: 261850
Join Date: Oct 2010
Chapter/Region: BAIC
Location: Oakland
Vehicle:
1994 RS
Red

Default

ditto151 is offline   Reply With Quote
Old 01-09-2011, 10:39 PM   #19
AQ Motorsports
Former Vendor
 
Member#: 60836
Join Date: Apr 2004
Chapter/Region: SCIC
Location: Torrance, CA
Vehicle:
2006 Mod Class STI
TIMEATTACK!!

Default

What he's not showing you is how they line up with the passages in the head. That little tiny section of block that's showing with the "older" gasket is not the important part. That gasket is only meant for the 08+ sti which has different coolant passages in the head, so if you use it on something else you'll actually be blocking off more of the coolant passages. I do agree that for a phase 2 motor you should not use the stock gasket.

So, to summarize
for a phase 1 n/a 2.5, use 11044AA610
for a phase 2 n/a 2.5, use 11044AA642 which is the 04-06 sti EJ255 gasket

Additionally, you can't use 11044AA642 or 11044AA770 (the one in the video) on a phase 1 2.5 because they are thinner and will cause your pistons to contact the head.

Last edited by AQ Motorsports; 01-09-2011 at 10:49 PM.
AQ Motorsports is offline   Reply With Quote
Old 01-09-2011, 11:28 PM   #20
ditto151
Scooby Newbie
 
Member#: 261850
Join Date: Oct 2010
Chapter/Region: BAIC
Location: Oakland
Vehicle:
1994 RS
Red

Default

but if i were to get cosworth i should get 1.5mm with a 101 bore
ditto151 is offline   Reply With Quote
Old 01-10-2011, 01:25 AM   #21
williaty
Scooby Guru
 
Member#: 71092
Join Date: Sep 2004
Chapter/Region: MWSOC
Location: Delaware County, Ohio
Vehicle:
2005 2.5RS Wagon
Regal Blue Pearl

Default

Quote:
Originally Posted by Harman Motive, Inc. View Post
What he's not showing you is how they line up with the passages in the head. That little tiny section of block that's showing with the "older" gasket is not the important part. That gasket is only meant for the 08+ sti which has different coolant passages in the head, so if you use it on something else you'll actually be blocking off more of the coolant passages. I do agree that for a phase 2 motor you should not use the stock gasket.
To reiterate what HM said, it's the way the gasket lines up with the head that matters. The block is nearly irrelevant. The head is always the limiting factor. So, basically, the guy in the video is an idiot.
williaty is offline   Reply With Quote
Old 01-10-2011, 01:26 AM   #22
williaty
Scooby Guru
 
Member#: 71092
Join Date: Sep 2004
Chapter/Region: MWSOC
Location: Delaware County, Ohio
Vehicle:
2005 2.5RS Wagon
Regal Blue Pearl

Default

Quote:
Originally Posted by ditto151 View Post
but if i were to get cosworth i should get 1.5mm with a 101 bore
Don't get a Cosworth gasket, it's a waste of money for you. Money that's better off spent properly prepping the head and block for use with an OEM MLS gasket.

Stop obsessing about the gasket and just do the work correctly.
williaty is offline   Reply With Quote
Old 01-10-2011, 03:38 AM   #23
ditto151
Scooby Newbie
 
Member#: 261850
Join Date: Oct 2010
Chapter/Region: BAIC
Location: Oakland
Vehicle:
1994 RS
Red

Default

i will get the factory gaskets thanks for putting it so clearly i am little slow at times

Last edited by ditto151; 01-10-2011 at 08:38 AM.
ditto151 is offline   Reply With Quote
Old 01-13-2011, 12:01 PM   #24
mattmak
Scooby Newbie
 
Member#: 211128
Join Date: May 2009
Location: Ontario, Canada
Vehicle:
2005 2.5RS 5MT Sedan
PSM

Default

does anyone know the thickness of the oem head gaskets?

for 2005 NA, I'm guessing part number 11044AA633?

I'm trying to calculate compression ration change for my engine build..

cheers,
M
mattmak is offline   Reply With Quote
Old 01-13-2011, 03:54 PM   #25
AQ Motorsports
Former Vendor
 
Member#: 60836
Join Date: Apr 2004
Chapter/Region: SCIC
Location: Torrance, CA
Vehicle:
2006 Mod Class STI
TIMEATTACK!!

Default

do not get that part number. It is a single layer coated gasket which will leak again. Use the STi gasket ending in 642 I mentioned above. They are the same thickness (I don't know the exact measurement off the top of my head).

Also here is an 08+ sti head:



you can see why the new -770 gasket is needed.
AQ Motorsports is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
what tire pressure to run stock? and what is a good aftermarket tire? jay25RS Tire & Wheel 6 06-13-2011 02:54 PM
what is in an overhaul gasket kit? upjeeper Built Motor Discussion 8 10-17-2007 09:29 PM
Is this a head gasket issue? problemcat13 Service & Maintenance 13 01-01-2007 10:25 PM
What is a good/very good 10" subwoofer KapaFool Alaskan Impreza Club Forum -- AKIC 21 04-28-2004 03:23 AM
what size turbo or what is a good kit? WiCKeDBLuREX Factory 2.0L Turbo Powertrain (EJ Series Factory 2.0L Turbo) 7 09-22-2002 12:51 PM


All times are GMT -4. The time now is 03:39 AM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2014 Axivo Inc.
Copyright ©1999 - 2014, North American Subaru Impreza Owners Club, Inc.