View attachment 24168 So i wanted to know if this is a big problem, 2.0 heads bored out width not depth to a 2.5. The confusing part is I was told the hybrid setup was a solid setup and a lot of people ran this setup with great success! But my real question is, is this style of heads needed or is someone trying to make a buck!?!?!?! ------------------------------------------------------------ Price: $400.00 Import Image Racing will beat or meet any competitors pricing! The Problem: As most people know, when you run a Subaru 2.5 shortblock with 2.0 heads, the compression ratio is too high to run safely and efficiently especially on pump fuel. The common approach to resolve this issue has been 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 thecombustion chamber that can build up heat and cause knock. This makes the engine less efficient than a full EJ257 with EJ257 heads. While some of these setups can tune ok, they generally experience inconsistencies under sustained full throttle operation. Drivability and fuel economy are also adversely affected. Some have also tried using custom pistons to bring down the compression ratio, but this has a very similar effect to a thicker head gasket. Our Solution: Instead of using a thicker head gasket or low compression pistons, we decided to try something a bit different. We worked closely with our machine shop to carefully 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 and combustion chamber shape of a complete STI engine. This improves the effectiveness of the quench area and the overall efficiency of the engine. The results with this approach show big improvements 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 a 2.5l STI rather than a 2.0l WRX.
Lots of folks running the hybrid without issue, many for many thousands of miles. Do not concern yourself with things like this.
They make the combustion chamber a replica of the EJ257. This allows for use of the pistons made for the EJ257. It also allows for similar tuning style to the 2.5L since it is the same combustion chamber style. It pretty much is like an EJ257 for internal specs. This does make it easier to buy off-the-shelf pistons since almost all are made for the EJ257 anyway. Bore matching is really good to have. It doesn't have to be an EJ257 shape. The D25 EJ255 doesn't have the same combustion chamber as the B25/V25B/W25 EJ257 heads. The chambers of the D25 heads are 97mm wide where the EJ257 are 99.5mm wide.
You still don't need it. I'm running the EJ257 case with 257 standard sized Mahle pistons with stock mill WRX 2.0 heads without issue. And I've been doing so now for nearly 4 years.
getting 157mpg in a 2002 wrx. ¿13gal tank? stock wrx injectors, TDO4, 2.5 block 2.0 heads, 1572 miles on the block changed the oil at 1500. been trying 2 drive conservative. im thinking its the turbo seeing its fully spooled at 2900 rpm don't know when the actuator opens for the exhaust. Only running 11 for boost. I drive about 40 miles to work every day and this is starting to get to me!!
I'm guessing you mean till the fuel light comes on? Typically the light comes on when you have between 3 to 4 gallons left in the tank. Which if we go with the 3gal mark, you're getting around 12mpg. What is your daily commute, and how long do you let it idle before driving? That still sounds pretty terrible.
highway for 38 miles and traffic lights for 2 miles. i let it idle for 5-10 min depending on weatheri
-My work/home commute is approximately 20 miles to and fro. City driving -I usually have a full tank monday morning, but by friday my tank is down to 1/4 mark. -Thus, i probably get 120 miles from a full tank just from city driving. -Highway ~250miles (could be less) on full tank ( if im nice to stay out of boooost) * Stg 2 STi * E85 * ~830cc injectors * 2-3mins of idling in the morning & evening = 6mins Total She is one gas guzzler *sigh*
Average 30% But with a good right foot, you can get decent mileage with E. Lol but who has that, especially with a subaru.
Why would you use 2.0L heads in the first place? Isn't the 2.5L SOHC head superior to everything else? It seems silly to even start with this approach, especially for turboed cars where you're already going to be tossing in forged pistons anyways to get whatever compression you want. Heck, if you wanted off boost power, you could probably even run cams suited for a NA motor which from my understanding versus turboed cams is something akin to a big turbo cam anyways. I guess I just don't see the point of the 2.0L heads in the first place.
Wow, no, the SOHC 2.5 head is terrible for turbo, just ask bielke55 and munkyking, they just werent made to make big HP. Also, n/a cams have too much overlap to make big power in turbo applications, basicly you are just blowing boost right back out the exhaust. Do a bit of research, the MAIN reason for running the 2.0 head on the 257 is because its easy, and you dont have to mess with the AVCS that the 257/255 heads have/use, plus the little boost in CR (and the bigger displacement) make it much more enjoyable off boost. Have you ever driven a 2.0 wrx, even stage 2 and tried to stay out of boost? They are pooches.
