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03-01-2010, 06:05 PM | #1 |
Former Vendor
Member#: 26933
Join Date: Oct 2002
Chapter/Region:
BAIC
Location: Fairfield, CA
Vehicle:2006 STI CGM |
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. |
03-01-2010, 06:07 PM | #2 |
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Congrats ed!
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03-01-2010, 06:21 PM | #3 |
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< wow! nice. keep the hybrid ideas coming :-)
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03-01-2010, 06:52 PM | #4 |
Scooby Specialist
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MWSOC
Location: grove city ohio
Vehicle:04 sti 10.41@141 on e85@ 30psi--spinning |
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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03-01-2010, 07:42 PM | #5 | |
Former Vendor
Member#: 26933
Join Date: Oct 2002
Chapter/Region:
BAIC
Location: Fairfield, CA
Vehicle:2006 STI CGM |
Quote:
Thanks -- Ed |
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03-01-2010, 07:56 PM | #6 |
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Vehicle:02 WRX vf39 |
Does this require new valve seats or any other parts?
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03-01-2010, 08:18 PM | #7 |
Former Vendor
Member#: 26933
Join Date: Oct 2002
Chapter/Region:
BAIC
Location: Fairfield, CA
Vehicle:2006 STI CGM |
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03-01-2010, 08:18 PM | #8 |
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This is a good option for those who want to run the same compression ratio as the STi.
Congrats! |
03-01-2010, 08:27 PM | #9 |
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Pretty fair price also!
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03-01-2010, 09:09 PM | #10 | |
Scooby Specialist
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Vehicle:04 sti 10.41@141 on e85@ 30psi--spinning |
Quote:
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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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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? |
03-02-2010, 12:31 PM | #13 |
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^^^+1000
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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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03-02-2010, 03:09 PM | #15 | |
Former Vendor
Member#: 26933
Join Date: Oct 2002
Chapter/Region:
BAIC
Location: Fairfield, CA
Vehicle:2006 STI CGM |
Quote:
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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03-02-2010, 03:15 PM | #16 |
Former Vendor
Member#: 26933
Join Date: Oct 2002
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BAIC
Location: Fairfield, CA
Vehicle:2006 STI CGM |
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03-02-2010, 04:24 PM | #17 |
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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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03-02-2010, 10:14 PM | #18 | |
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Quote:
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03-02-2010, 10:55 PM | #19 |
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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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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. |
03-02-2010, 11:05 PM | #21 |
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Good price, but this isnt anything new.
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03-02-2010, 11:05 PM | #22 |
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What is the disassembly/assembly cost?
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03-03-2010, 01:30 AM | #23 |
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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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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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03-03-2010, 08:34 AM | #25 |
Scooby Guru
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^^^ Its the bore, and volume thats is oppened up...
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