Exciting New Head Option for EJ205/EJ257 Hybrid Builds!
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Exciting New Head Option for EJ205/EJ257 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 safely run. 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 shrinking 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 greatly improves the quench area and 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 heads and its $450 for a set of heads.
Thanks
-- Ed
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 greatly improves the quench area and 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 heads and its $450 for a set of heads.
Thanks
-- Ed
Last edited by EQ Tuning; Aug 7, 2013 at 11:23 AM.
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Seems like a useful option to give folks...especially if they don't plan to swap out to forged pistons with a STi stock short block.
our calculations have come up with when doing stock WRX heads with stock STi (or stock compression STi forged pistons) to be 9.0-9.2:1 *Way to high in our opinions*
I would have to say that not everyone uses thicker head gaskets when doing hybrid builds. I know we have never used thicker head gaskets as it only changes the compression by 0.2 when using a 1.1mm gasket (which is very insignificant and why we never do it that way). We use forged pistons designed for the 2.0L WRX chambered heads.
-Noah
our calculations have come up with when doing stock WRX heads with stock STi (or stock compression STi forged pistons) to be 9.0-9.2:1 *Way to high in our opinions*
I would have to say that not everyone uses thicker head gaskets when doing hybrid builds. I know we have never used thicker head gaskets as it only changes the compression by 0.2 when using a 1.1mm gasket (which is very insignificant and why we never do it that way). We use forged pistons designed for the 2.0L WRX chambered heads.
-Noah
Last edited by LICmotorsports; Feb 5, 2010 at 05:29 PM.
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Seems like a useful option to give folks...especially if they don't plan to swap out to forged pistons with a STi stock short block.
I would have to say that not everyone uses thicker head gaskets when doing hybrid builds. I know we have never used thicker head gaskets as it only changes the compression by 0.2 when using a 1.1mm gasket (which is very insignificant and why we never do it that way). We use forged pistons designed for the 2.0L WRX chambered heads.
-Noah
I would have to say that not everyone uses thicker head gaskets when doing hybrid builds. I know we have never used thicker head gaskets as it only changes the compression by 0.2 when using a 1.1mm gasket (which is very insignificant and why we never do it that way). We use forged pistons designed for the 2.0L WRX chambered heads.
-Noah
We've played around with many different options for the hybrid setups including thicker head gaskets, custom pistons, and actual EJ257 heads w/o AVCS. This CNC method turns out similarly to the EJ257 heads but at a much cheaper price than buying new STI heads and AVCS hardware.
Thanks
-- Ed
Last edited by EQ Tuning; Feb 5, 2010 at 05:50 PM.
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. While its easier to run the higher compression ratio on higher octane fuel, the efficiency added by the improved shape of the combustion chamber and quench area is still very significant even with E85 or race fuel.Thanks
-- Ed
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Thanks
-- Ed
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A little update on this... We've gone through a full break-in and full tune on a couple of these hybrid setups and I am extremely happy to see the results I was expecting.
This is an 04 WRX with an EQ Stage 1 Shortblock and EQ CNC Machined EJ205 heads. This car has a VF43, DW750cc injectors, and supporting mods:
While the power levels and curves are great all around, the really impressive part is in how the car tuned out, feels and drives. The new combustion chamber design allowed for a lot more timing advance in the mid range which really helped fill out the torque curve and also really helped with the extremely smooth drivability and response that these motors are exhibiting. I have tuned a lot of different hybrid setups in the past and I honestly have never felt any other hybrid drive as smoothly and consistently as these builds have been running.
Thanks
-- Ed
This is an 04 WRX with an EQ Stage 1 Shortblock and EQ CNC Machined EJ205 heads. This car has a VF43, DW750cc injectors, and supporting mods:
While the power levels and curves are great all around, the really impressive part is in how the car tuned out, feels and drives. The new combustion chamber design allowed for a lot more timing advance in the mid range which really helped fill out the torque curve and also really helped with the extremely smooth drivability and response that these motors are exhibiting. I have tuned a lot of different hybrid setups in the past and I honestly have never felt any other hybrid drive as smoothly and consistently as these builds have been running.
Thanks
-- Ed
Last edited by EQ Tuning; Feb 27, 2010 at 04:51 PM.