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Old 03-01-2010, 06:05 PM   #1
Equilibrium Tuning
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Default Exciting New Head Option for EJ20/EJ25 Hybrid Builds!

We are excited to announce that we have a great new option for the 2.0/2.5 hybrid folks! As most people know, when you run a 2.5l shortblock with 2.0l heads, the compression ratio is too high to run safely and efficiently. The common approach to resolve this is to use a thicker head gasket to try to bring the compression ratio down. While this can bring the overall compression ratio down, it is by no means ideal. The resulting combustion chamber shape remains inefficient since you're leaving the 2.0l chamber in the heads untouched. You are in essence reducing the effectiveness of the quench area and introducing several sharp edges to the combustion chamber that can build up heat and cause knock. This makes the engine less efficient than a full EJ257 with EJ257 heads.

Instead of using a thicker head gasket, we decided to try something a bit different. We worked closely with our machine shop to actually map out the combustion chamber of the EJ257 STI head and create a CNC program to replicate the exact same chamber every time. Using this program, we then set up the 2.0l head castings in the CNC and machine out an exact copy of the 2.5l combustion chamber into each 2.0l head casting. We are then able to use a quality OEM head gasket and maintain the exact compression ratio of a complete STI engine. This improves the effectiveness of the quench area and the overall efficiency of the engine because you now have the exact same combustion chamber as a full EJ257.

We have done several hybrid builds with this approach now and have seen great results not only in overall power output, but especially in terms of crisp, smooth off-boost drivability and torque. We've also seen a significant increase in fuel economy as compared to a standard hybrid build. From a tuning standpoint, the difference is so significant that we had to spend quite a bit of time building new base maps for these builds. Under low load conditions, these setups can run as much as 15-20 degrees more timing advance than a hybrid build with a thicker head gasket. This was a great thing to see as we end up with a timing curve much more similar to an STI rather than a 2.0l WRX.

This service is available for any EJ205 and EJ207 heads and its $500 for a set of heads.

Please download and fill out this order form when placing an order or sending in heads: http://eqtuning.com/forms/EQ-HEAD-FORM.pdf

Here are some pictures of the process:








And final product:



*** UPDATE: We can now perform the same service for EJ207 heads! ***

Thanks
-- Ed
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Last edited by Equilibrium Tuning; 07-15-2014 at 06:48 PM.
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Old 03-01-2010, 06:07 PM   #2
rmkcent
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Congrats ed!
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Old 03-01-2010, 06:21 PM   #3
25rsti
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< wow! nice. keep the hybrid ideas coming :-)
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Old 03-01-2010, 06:52 PM   #4
john 1badSTI
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congrats on the cnc program but I know Dominic from maxwell power as well as myself have always bore matched the combustion chambers on the hybrids we have built.Once again good job on making a cnc program.
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Old 03-01-2010, 07:42 PM   #5
Equilibrium Tuning
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Quote:
Originally Posted by john 1badSTI View Post
congrats on the cnc program but I know Dominic from maxwell power as well as myself have always bore matched the combustion chambers on the hybrids we have built.Once again good job on making a cnc program.
Yep I definitely know that modifying the combustion chamber is not a new idea, but the CNC program is really helping to keep things consistent and precise. Its also nice to know that the result is an exact copy of the STI CC. I'll have to take some pictures of the process next time we're doing one.

Thanks
-- Ed
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Old 03-01-2010, 07:56 PM   #6
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Does this require new valve seats or any other parts?
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Old 03-01-2010, 08:18 PM   #7
Equilibrium Tuning
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Does this require new valve seats or any other parts?
Nope... most of the material that's removed is on the outer perimeter of the combustion chamber and the valve seats are untouched.

Thanks
-- Ed
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Old 03-01-2010, 08:18 PM   #8
FuJi K
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This is a good option for those who want to run the same compression ratio as the STi.

Congrats!
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Old 03-01-2010, 08:27 PM   #9
Token-Negro
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Pretty fair price also!
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Old 03-01-2010, 09:09 PM   #10
john 1badSTI
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Quote:
Originally Posted by Equilibrium Tuning View Post
Yep I definitely know that modifying the combustion chamber is not a new idea, but the CNC program is really helping to keep things consistent and precise. Its also nice to know that the result is an exact copy of the STI CC. I'll have to take some pictures of the process next time we're doing one.

Thanks
-- Ed
hey ed it would be even cooler to make a short video to watch it being down in action.+1 most guys on here have never seen a cnc machine at work.
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Old 03-01-2010, 10:42 PM   #11
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Hey Ed Im glad you posted this over here, theres quite a few hybrids over here.
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Old 03-02-2010, 12:25 PM   #12
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Ed --

People seem to favor the D25 chamber shape over the STi B25 / V25 chamber shape. I can't find the comment, but I thought you also noted something to the extent of 2.5L WRXes tending to make slightly more power than the STis with similar mods.

I know it's a small difference, but I'm just curious why you chose to replicate the STi chamber instead of the D25 casting chamber?
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Old 03-02-2010, 12:31 PM   #13
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^^^+1000
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Old 03-02-2010, 02:28 PM   #14
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Ed, how would you like the heads to arrive? Empty? Or with valves and springs?
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Old 03-02-2010, 03:09 PM   #15
Equilibrium Tuning
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Quote:
Originally Posted by Concillian View Post
Ed --

People seem to favor the D25 chamber shape over the STi B25 / V25 chamber shape. I can't find the comment, but I thought you also noted something to the extent of 2.5L WRXes tending to make slightly more power than the STis with similar mods.

I know it's a small difference, but I'm just curious why you chose to replicate the STi chamber instead of the D25 casting chamber?
I haven't seen 2.5l WRX's make any more power than a similarly set up STI. Actually I usually see the 2.5l WRX's taper off peak power more severely up top as compared to the STI. I think that has to do with the higher CR and the resulting drop in timing up top.

I think you might be thinking about using the EJ255 shortblock for hybrid builds. Since the EJ255 pistons are dished more than the EJ257 pistons, this would bring the CR down as compared to using an EJ257 shortblock. Using the D25 chamber with EJ257 pistons would actually create a very high CR which is counter productive .

Thanks
-- Ed
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Old 03-02-2010, 03:15 PM   #16
Equilibrium Tuning
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Quote:
Originally Posted by sidewayz View Post
Ed, how would you like the heads to arrive? Empty? Or with valves and springs?
If you want to save some money, they should come in empty. We're always happy to disassemble and re-assemble them for you, but we do have to charge for that service.

Thanks
-- Ed
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Old 03-02-2010, 04:24 PM   #17
PSolbergfan
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I have set of new, undressed ej205 heads. When I get the money I'm totally doing this!!!
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Old 03-02-2010, 10:14 PM   #18
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Quote:
Originally Posted by Concillian View Post
Ed --

People seem to favor the D25 chamber shape over the STi B25 / V25 chamber shape. I can't find the comment, but I thought you also noted something to the extent of 2.5L WRXes tending to make slightly more power than the STis with similar mods.

I know it's a small difference, but I'm just curious why you chose to replicate the STi chamber instead of the D25 casting chamber?
correct me if i'm wrong, but d25 is the ej255 head right? i assume you simply couldn't do it because according to this thread the ej205 and ej255 have roughly the same volume.
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Old 03-02-2010, 10:55 PM   #19
bettyblue
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a little off topic, but what would be an ideal head gasket to use after performing this?
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Old 03-02-2010, 10:56 PM   #20
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Well, I wouldn't call it a "very high" CR at 8.78:1. However, the D25 will only knock off 1 point compared to the WRX S20 heads (8.88:1).

D25 chamber machining, if possible, would be a good option for meth/E85, and some pump applications.
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Old 03-02-2010, 11:05 PM   #21
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Good price, but this isnt anything new.
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Old 03-02-2010, 11:05 PM   #22
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What is the disassembly/assembly cost?
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Old 03-03-2010, 01:30 AM   #23
deezel_d
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i am a noob here but trying to do a hybrid i have a built 257 and a complete ej20k that i was gonna use the heads off of.....do i have to do same thing with these heads..
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Old 03-03-2010, 02:44 AM   #24
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Why not design the machining process to mimic the ej207 heads? Those are after all the most efficient best flowing heads Subaru produces no?
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Old 03-03-2010, 08:34 AM   #25
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^^^ Its the bore, and volume thats is oppened up...
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