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Old 06-07-2010, 01:40 PM   #126
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Originally Posted by 2slofouru View Post
I do agree more conclusive data would add to this thread. I'm in the same boat about to use my 97 ej20k heads on my 97 ej25d block with sti takeout pistons and ? rods and 75mm phase 2 crank. I'm having trouble wrapping my head around the combined concept of ideal compression, quench area, VE etc. I've seen subaru n/a engines make big power running relatively low boost so it would seem anything below the compression the n/a guys run would be safe with aftermarket EM. I'm running apex'i pfc btw and will be getting a competent tuner to set it up.
The compression ratio is just one part of the equation. If you have consistent 93+ Octane available in your area, slightly higher compression won't necessarily hurt you significantly but you will not be able to run as much boost. Depending on the turbo you run, this may be good or bad. The other factor, however, is the edge of the combustion chamber in the 2.0 heads building up heat and causing knock. This is going to be true no matter what compression ratio you're running, so I would recommend at the very least deshrouding the edges of the combustion chamber in that case.

-- Ed
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Old 06-07-2010, 09:32 PM   #127
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The edges of the combustion chamber protrude into the 2.0l cylinder already.... its the "clover" design. Wish I could compare the heads to the sti pistons coming in the mail but the heads are on my daily driver.
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Old 06-08-2010, 10:00 AM   #128
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If you rechecked the lash after torquing the heads down, you would see that it can change significantly. You may have gotten lucky and kept your lash close to spec, but that won't always be the case. Check the Subaru service manual as it also instructs to set lash with the heads on the block. Cosworth also never sends heads out with lash set for this reason.

Thanks
-- Ed
forgot to mention that I used the cosworth worksheet: http://www.cosworthusa.com/store/pc/...ds%20v1.0a.pdf when i set the valve lash. Nowhere does it mention that its necessary to perform the lash while the heads are torqued to the block...the worksheet also illustrates the process and they are lashing the valves right on a bench. Also some people like to alternatively shave the valve tips a tiny bit to set the lash...it would be a pain to do this if the heads have to be torqued to check the clearance then removed....
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Old 06-08-2010, 11:52 AM   #129
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Like I said, we are happy to set the valve lash off the block but highly recommend confirming the lash settings once the heads are torqued down. I'll look up the factory service manual procedure for you a bit later.

-- Ed
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Old 06-08-2010, 12:03 PM   #130
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Like I said, we are happy to set the valve lash off the block but highly recommend confirming the lash settings once the heads are torqued down. I'll look up the factory service manual procedure for you a bit later.

-- Ed
thanks Ed
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Old 06-09-2010, 03:32 AM   #131
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I can personally vouch for needing the heads torqued down to properly set the lash. I set the lash on the bench, and had to fix 7 if I remember correct, after I torqued the head. And the change needed to go both directions (some too tight and some too loose).

So Ed - Is the $400 the total price to clean the heads and then open the combustion chamber and ship them back? Or is the $400 jus the cnc time and it's extra for shipping and cleaning etc...?

Next question - You say it's a 2-week turnaround: does this mean you have 2 weeks of backlog, or the process takes 2 weeks, or 2 weeks is just a worst-case estimate in case you want to close shop for a few days to vacation?

I ask because I am local (sort of) and would be willing to drop the heads off and pick them up if we could work out a faster solution...

My car is my only mode of transportation and so I'd I'd need as little downtime as possible... Any expedited same-day service offered?
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Old 06-09-2010, 01:48 PM   #132
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I can personally vouch for needing the heads torqued down to properly set the lash. I set the lash on the bench, and had to fix 7 if I remember correct, after I torqued the head. And the change needed to go both directions (some too tight and some too loose).

So Ed - Is the $400 the total price to clean the heads and then open the combustion chamber and ship them back? Or is the $400 jus the cnc time and it's extra for shipping and cleaning etc...?

Next question - You say it's a 2-week turnaround: does this mean you have 2 weeks of backlog, or the process takes 2 weeks, or 2 weeks is just a worst-case estimate in case you want to close shop for a few days to vacation?

I ask because I am local (sort of) and would be willing to drop the heads off and pick them up if we could work out a faster solution...

My car is my only mode of transportation and so I'd I'd need as little downtime as possible... Any expedited same-day service offered?
I'm glad someone else has seen the lash variances. We tried to come up with a pattern to follow as well, but there's no such pattern. It makes it significantly more complicated for us to set the lash once the heads are bolted down, so we didn't come to that decision lightly .

The $400 is just for the CNC service. That's assuming we get bare castings and there is no cleaning included. We always recommend a valve job before re-assembling the heads, so the cleaning should be done then. We can of course disassemble the heads for you and provide cleaning at an additional cost. We also offer quality valve jobs and re-surfacing, in which case we do all the disassembly, cleaning, and re-assembly.

The 2 week turnaround just gives us a safe time span. We can expedite if necessary, especially on local jobs. 1 day turnaround is not possible, however . Please give us a call if you'd like more info.

Thanks
-- Ed
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Old 06-09-2010, 01:49 PM   #133
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The edges of the combustion chamber protrude into the 2.0l cylinder already.... its the "clover" design. Wish I could compare the heads to the sti pistons coming in the mail but the heads are on my daily driver.
What heads are these? Are they from an NA application?

-- Ed
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Old 06-09-2010, 03:06 PM   #134
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Sweet high compression head! Looks like a really good quench design to my n00bish eyes. Direct the A/F mixture from all directions towards the spark plug. Nice!

Yes, what head is this?

Wonder what the Subaru engineers think of the head 'modification' detailed in this thread. Like, 'man, we freaking painstakingly designed the head to direct the mixture towards the spark plug and now this dude on the internetz is machining it all away!' j/k

Last edited by MRF582; 06-09-2010 at 07:10 PM.
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Old 06-09-2010, 06:11 PM   #135
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Wonder what the Subaru engineers think of the head 'modification' detailed in this thread. Like, 'man, we freaking painstakingly designed the head to direct the mixture towards the spark plug and now this buttmunch on the internetz is machining it all away!' j/k

Considering we're machining in an exact copy of a combustion chamber that Subaru designed for one of their highest performing engines, I doubt the engineers would have that reaction.

Do a little reading and you'll see that having a large quench area like in the heads pictured is mainly beneficial in NA applications. That's why the Subaru engineers did away with most of the quench area on their turbo applications.

-- Ed
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Old 06-09-2010, 11:59 PM   #136
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What heads are these? Are they from an NA application?

-- Ed
Jdm 1997 wrx sedan ej20k head

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Originally Posted by MRF582 View Post
Sweet high compression head! Looks like a really good quench design to my n00bish eyes. Direct the A/F mixture from all directions towards the spark plug. Nice!

Yes, what head is this?

Wonder what the Subaru engineers think of the head 'modification' detailed in this thread. Like, 'man, we freaking painstakingly designed the head to direct the mixture towards the spark plug and now this dude on the internetz is machining it all away!' j/k
This head is completely stock aside from the surface job, its a low compression turbo head

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Originally Posted by Equilibrium Tuning View Post

Considering we're machining in an exact copy of a combustion chamber that Subaru designed for one of their highest performing engines, I doubt the engineers would have that reaction.

Do a little reading and you'll see that having a large quench area like in the heads pictured is mainly beneficial in NA applications. That's why the Subaru engineers did away with most of the quench area on their turbo applications.

-- Ed

This engine was rated a 280 at the crank bone stock (from only 2 liters) in 1997 and feels like more. I'm pretty sure its a fairly good design.
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Old 06-10-2010, 01:43 AM   #137
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Looks like you added some good data there 2slofouru! Thanks!

That engine might have been a low compression unit (lower compression pistons?) but that head looks to have a lower combustion chamber volume than my stock 04 WRX USDM 2.0L head? If so, then mated to my short block, the compression ratio should increase. This is fantastic news!

Anyone have access to this head out of the car to measure its volume?
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Old 06-10-2010, 04:31 AM   #138
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I'll add my 2c on the squish area discussion...
A good squish area most of the time it's a good thing (look the squish area of that damn 2stroke engines with more that 300hp/l at 20'000rpm...), because it create a turbolence that permit a faster and homogeneous burn of the charge (good thing).
BUT, if you loose a bit of efficiency due to slower and inefficient burn, at the same comp ratio/charge temps, etc, can allow an increase in turbo pressure.
You get less 'jiuce' off boost, and more power on boost.
Said that, there isn't a true winner. If the car is street driver, a good squish area can save fuel and have better off-bost performance, but if you use the car only in boost (rally/race/etc) it's best to have a bit less efficiency but still more power.
Look at the modification on the wrc heads on the RCM site, the squish area on the v1-v4 heads are angled to reduce the effect of the squish. Simply, with all the other variables the same, with a 'worst' squish area you can gain more power.
And in any case, retarding the timings isn't a too 'natural' procedure. You loose in any case efficiency (instead of have the peak pressure at NEAR 14 like ideal, you move it far away), with the drawback that you are moving heat to the exhaust valves and components, that can fail under this extremes conditions.

In any case, for more power you need to pay something.
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Old 06-10-2010, 07:56 AM   #139
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Here are the pistons and head when I was splitting the block to check the internals. I believe compression was around 140psi on all cylinders, I'll have to check to be sure.
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Old 06-10-2010, 10:59 AM   #140
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And in any case, retarding the timings isn't a too 'natural' procedure. You loose in any case efficiency (instead of have the peak pressure at NEAR 14 like ideal, you move it far away), with the drawback that you are moving heat to the exhaust valves and components, that can fail under this extremes conditions.

In any case, for more power you need to pay something.
What if you make a change that increases the speed of flame front propagation? Then you need to ignite the mixture later to get peak cylinder pressure at near 14 degrees ATDC.

2slofouru, those pistons, from a distance, certainly look ordinary. But pictures alone aren't giving us enough details to judge compression ratio. The connecting rod/piston assembly could be shorter so the distance between the top of its stroke and the deck is greater in that engine than my USDM engine? Maybe they did that so the engine would be a little less 'interferceny' and would tolerate more cam gear misalignment before valve to piston contact?

Cylinder head combustion chamber volume data would be nice.
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Old 06-10-2010, 11:13 AM   #141
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What if you make a change that increases the speed of flame front propagation? Then you need to ignite the mixture later to get peak cylinder pressure at near 14 degrees ATDC.
Obviously you can't have all! There is a limit on how fast can travel the flame front, you can't retard forever. More fast = less stable, a nigthmare to tune and prone do detonation with minimal change in temperature or minimal errors in the advanve table.
It's a no way mate, with all other variables the same, too squish can limit top power.
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Old 06-10-2010, 11:32 AM   #142
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For not speak that at high engine speeds/high during the compression stroke the charge that is in the squish band wil be futher compressed (so a local increas in temperature) before start to move in the center of the combustion chambre. There will be also a similar effect to an 'hydrolock'. That's why on 2t engines the squish area have a different angle than the one on the piston (2-4 difference),this decrease the effect of the squish band, but reduce the risk of detonation.
In the engine that i'm building i'm using v4 sti heads (with that large quench areas), and i'm planning to machine the combustion chambers with the squish area with that small angle, and a TIGHT piston/head clearance. This can be a good balance...
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Old 06-18-2010, 03:08 PM   #143
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bump.
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Old 06-18-2010, 03:35 PM   #144
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What was your compression ratio before and after? Can you post before and after dyno charts or 1/4 mile trap speeds? Define 'noticeable increase in fuel mileage' using numbers. We like numbers here... Quantitative data good! Me likey.
Are you capable of going into a thread without the urge to take a dump in it?

No ****, we all would love heaps of data for every modification, but that isn't how the aftermarket tuning world works. No on has a GM/FORD budget to figure out, to a reasonable degree of scientific certainly, if taking a few CCs out of the 2.0L chamber really makes the motor that much more efficient. What we do have, however, is ample anecdotal evidence from the guys out there tuning these things every day, all of whom seem to agree that, when the chamber is opened up, the car reacts to tuning in a more predictable manner, and much more like other Subaru vehicles which came equipped with a 2.5L motor and accompanying combustion chamber.

P.S.: I don't care if you are an engineer.
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Old 06-18-2010, 03:42 PM   #145
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I think he's really looking at it the same way that I am. Without data we aren't sure if this is the best or most efficient(hate the improper use of this word) solution for the given issue.

i.e. If the compression ratio/dish design is the cause for the given changes...thus a proper piston, an already desirable part to change, may be a simple solution that could yield equal or better results...
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Old 06-18-2010, 05:23 PM   #146
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i.e. If the compression ratio/dish design is the cause for the given changes...thus a proper piston, an already desirable part to change, may be a simple solution that could yield equal or better results...
This.

I am a very skeptical person by nature. I buy my salt in bulk at Costco... Need it for forums such as this one.
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Old 06-18-2010, 06:27 PM   #147
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I think he's really looking at it the same way that I am. Without data we aren't sure if this is the best or most efficient(hate the improper use of this word) solution for the given issue.

i.e. If the compression ratio/dish design is the cause for the given changes...thus a proper piston, an already desirable part to change, may be a simple solution that could yield equal or better results...
I agree that there are other possible solutions. I've tried the piston route on a few cars and they didn't perform as well as the cars we've done with these heads. Simple as that. Have you tried this approach to prove that your lower compression pistons work as well or better?

FWIW, you approach this with a respectful manner, so I'm very happy to continue the discussion with you. The other guy does not, so I don't care to indulge him .

Thanks
-- Ed
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Old 06-21-2010, 09:57 PM   #148
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i wanna see finished product pics
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Old 06-21-2010, 11:41 PM   #149
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Simple as that. Have you tried this approach to prove that your lower compression pistons work as well or better?
No, I haven't. I am really curious though. In fact, the only 'low' compression order I've ever had was for one of my 2.43L long rod setups and that is a completely different animal.
I know that the quench pad design hasn't had any negative feedback. However, my test groups are still small
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Old 06-22-2010, 12:52 PM   #150
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i wanna see finished product pics
I'll get some up today.

-- Ed
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