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Old 01-15-2013, 11:47 PM   #26
WoodsWagon
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You can do the combustion chamber work yourself if you can't send it out to one of the shops that does CNC head milling.

Use the 2.5l headgasket to mark the cylinder bores on the heads, go by pictures of the 2.5l heads and use a burr and a flap wheel to open them up. CC the chambers and trim to get them all balanced. The aluminum is easy to work and you can get both heads done in a couple hours. Be patient and careful, you don't want to nick the valve seats or score across the deck surface.

Opening up the chambers is much better than using a thick headgasket because you don't loose the quench zones where the piston is nearly touching the head at TDC. That helps a lot with even combustion pressures and reduces the tendency to detonate.

The hybrid build I helped on was an 05 EJ257 shortblock with 02 EJ205 heads. Stock td04 and everything else.

The result ran great, but the car wasn't driven that much longer because the owner had a ton of other maintenance issues he hadn't taken care of and it was parked. It's now been sold to someone who's in the process of fixing it up right.
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Old 01-16-2013, 07:51 AM   #27
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Quote:
Originally Posted by WoodsWagon
You can do the combustion chamber work yourself if you can't send it out to one of the shops that does CNC head milling.

Use the 2.5l headgasket to mark the cylinder bores on the heads, go by pictures of the 2.5l heads and use a burr and a flap wheel to open them up. CC the chambers and trim to get them all balanced. The aluminum is easy to work and you can get both heads done in a couple hours. Be patient and careful, you don't want to nick the valve seats or score across the deck surface.

Opening up the chambers is much better than using a thick headgasket because you don't loose the quench zones where the piston is nearly touching the head at TDC. That helps a lot with even combustion pressures and reduces the tendency to detonate.

The hybrid build I helped on was an 05 EJ257 shortblock with 02 EJ205 heads. Stock td04 and everything else.

The result ran great, but the car wasn't driven that much longer because the owner had a ton of other maintenance issues he hadn't taken care of and it was parked. It's now been sold to someone who's in the process of fixing it up right.
My plan is to use the stock sti HG and just drop it in with no other work and see how it goes. Wgat should i expect for a compression ratio.
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Old 01-16-2013, 11:06 AM   #28
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Expect a higher than normal compression ratio, not sure the exact figures but if you search you'll find out. Since running higher than normAl compression ratio id suggest not to boost the hell out of this machine.
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Old 01-16-2013, 02:07 PM   #29
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Quote:
Originally Posted by danger1138
Expect a higher than normal compression ratio, not sure the exact figures but if you search you'll find out. Since running higher than normAl compression ratio id suggest not to boost the hell out of this machine.
Yeah I hear the higher compression is better for off boost driving and the turbo spools alot quicker. I only plan to be on about 17-20 pounds max on a 16G
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Old 01-16-2013, 03:17 PM   #30
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If your not doing head work, i would advise u to run thicker head gaskets. (Cometics)
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Old 01-16-2013, 03:39 PM   #31
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Quote:
Originally Posted by danger1138
If your not doing head work, i would advise u to run thicker head gaskets. (Cometics)
I don't wanna run a thicker HG. I should be fine with stock. Just gonna have a higher CR
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Old 01-16-2013, 03:56 PM   #32
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Yea if thats the route u wanna take. But usually most people wanna run higher boost, hence u would want lower or close to stock compression ratio.
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Old 01-16-2013, 04:09 PM   #33
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Quote:
Originally Posted by danger1138
Yea if thats the route u wanna take. But usually most people wanna run higher boost, hence u would want lower or close to stock compression ratio.
Yea I'm gonna have to sacrifice boost
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Old 01-16-2013, 04:54 PM   #34
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Yea that added torque with a hybrid is def worth it.
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Old 01-16-2013, 05:36 PM   #35
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I was gonna go stock sti hg in my hybrid also but my tuner convinced me it would be easier to tune and I would get more life out of my engine if I run a lower compression so he recommended .051 cometics. Also note that u have 8.9.1 pistons also so I would of been up there

Edit: compression came out at 10.1 so even with a thicker hg it's high

Last edited by 04ScoobyWtf; 01-16-2013 at 05:53 PM.
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Old 01-16-2013, 05:43 PM   #36
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Quote:
Originally Posted by 04WRX_Boost View Post
Yea I'm gonna have to sacrifice boost
My concern with your setup would be that you're using stock STi pistons, which are not known for their knock resistance. I would at least throw in some forged pistons for peace of mind, but to each their own. I don't deny it will be fun as a DD with high compression. Just make sure you have a very good tune and keep the boost low.
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Old 01-17-2013, 05:02 PM   #37
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Quote:
Originally Posted by 03SubyWRX

My concern with your setup would be that you're using stock STi pistons, which are not known for their knock resistance. I would at least throw in some forged pistons for peace of mind, but to each their own. I don't deny it will be fun as a DD with high compression. Just make sure you have a very good tune and keep the boost low.
Would you reccomend just getting the cometic thicker head gasket? To run more boost
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Old 01-17-2013, 05:45 PM   #38
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I would personally have the heads machined; I wouldn't bother running a hybrid without doing that. However, if you absolutely can't, then I'd run a thicker head gasket for more room to breathe when tuning it.
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Old 01-17-2013, 08:43 PM   #39
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Quote:
Originally Posted by 03SubyWRX
I would personally have the heads machined; I wouldn't bother running a hybrid without doing that. However, if you absolutely can't, then I'd run a thicker head gasket for more room to breathe when tuning it.
I'm gonna run a cometic, .51. Head gasket. Do they fail? What kind of CR should I see with this? Or should I go thicker ?
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Old 01-20-2013, 12:44 AM   #40
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Quote:
Originally Posted by 04WRX_Boost View Post
I'm gonna run a cometic, .51. Head gasket. Do they fail? What kind of CR should I see with this? Or should I go thicker ?
If your going with that thickness dont go with cometic, just go with OEM gaskets

But if your not getting the heads machined and going to use the HG to lower the compression ratio you would nee like a 1.1mm or 1.5 depending on what compression ratio you wanna go with
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Old 01-21-2013, 11:24 AM   #41
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Quote:
Originally Posted by dinggoo

If your going with that thickness dont go with cometic, just go with OEM gaskets

But if your not getting the heads machined and going to use the HG to lower the compression ratio you would nee like a 1.1mm or 1.5 depending on what compression ratio you wanna go with
I want the low end torque of the higher compression ratio, but I'm not sure exacly how much boost I will be safe on, 20? Maybe ?
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Old 01-22-2013, 05:12 PM   #42
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What does anyone think of the stock NA 2.5 head gasket
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Old 01-23-2013, 12:29 PM   #43
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working on my build. I'm waiting on the heads to get dome by Ed at Eq, then I can finaly get it put together. at the momen I have the following
New Ej257 2009+ with carillo rods and CP pistons with side skirt coating.
EJ205 heads CNC work is being done to the chambers by Ed, full P&P, BC 272 cams,
new Gates water pump and full timing kit, ARP head studs, OEM complete EJ205 gasket kit with OEM STI head gaskets, 11mm STi oil pump, K&N typhoon intake, Perrin catless up and down pipe, Cobb cat back, 06 sti trans, DW800cc injectors DW 200 fuel pump, Excedy light weight STI flywheel, Excedy stage 1 HD STI clutch. Up in the air about the turbo not sure if I want an FP green HTA or a Blouch 20G-xt.
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Old 01-24-2013, 06:12 AM   #44
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Quote:
Originally Posted by gfx2043 View Post
working on my build. I'm waiting on the heads to get dome by Ed at Eq, then I can finaly get it put together. at the momen I have the following
New Ej257 2009+ with carillo rods and CP pistons with side skirt coating.
EJ205 heads CNC work is being done to the chambers by Ed, full P&P, BC 272 cams,
new Gates water pump and full timing kit, ARP head studs, OEM complete EJ205 gasket kit with OEM STI head gaskets, 11mm STi oil pump, K&N typhoon intake, Perrin catless up and down pipe, Cobb cat back, 06 sti trans, DW800cc injectors DW 200 fuel pump, Excedy light weight STI flywheel, Excedy stage 1 HD STI clutch. Up in the air about the turbo not sure if I want an FP green HTA or a Blouch 20G-xt.
HTA FP green hands down. Love that turbo and would recommend it to anyone.
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Old 02-14-2013, 12:13 AM   #45
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Quote:
Originally Posted by 04WRX_Boost View Post
What does anyone think of the stock NA 2.5 head gasket
IDK about these gaskets but I believe the bore is different than the STI so you would need a wider HG
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Old 02-14-2013, 02:19 AM   #46
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Quote:
Originally Posted by dinggoo

IDK about these gaskets but I believe the bore is different than the STI so you would need a wider HG
Check your notes
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Old 02-26-2013, 04:00 AM   #47
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so whats safe boost level if your not using a thicker headgasket or chamber matching the heads?
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Old 02-26-2013, 04:01 AM   #48
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andrew himself at andrewtech told me he would NOT recommend to chamber match or use a thicker gasket.
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Old 02-26-2013, 09:37 AM   #49
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When you run a 2L head on a 2.5L block, especially the EJ257 with its pistons or pistons with the same dish, the compression ratio rises. You run less boost with the same timing. Wanna run the same boost, have to lower timing a little.

If you wanted to run a hybrid on pump gas, i would recommend getting pistons to lower the compression ratio to reduce detonation. If afraid of losing lowend torque? You shouldn't be because you have a 2.5L and you should drive according to your powerband. I have no problem driving a 2L around town.

If the quench really mattered, the pistons should have matched the chambers with a pad on them as well.
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Old 02-26-2013, 11:03 AM   #50
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Quote:
Originally Posted by FuJi K View Post
When you run a 2L head on a 2.5L block, especially the EJ257 with its pistons or pistons with the same dish, the compression ratio rises. You run less boost with the same timing. Wanna run the same boost, have to lower timing a little.

If you wanted to run a hybrid on pump gas, i would recommend getting pistons to lower the compression ratio to reduce detonation. If afraid of losing lowend torque? You shouldn't be because you have a 2.5L and you should drive according to your powerband. I have no problem driving a 2L around town.

If the quench really mattered, the pistons should have matched the chambers with a pad on them as well.
Ahhh wtf I can't decide what to do I just don't wanna spend the extra money to do it. When it's possible to have high compression and run less boost. Is it really that unsafe? I wouldn't think so
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