Rs block and dohc heads swap pros cons?

[waldo320]

Well I have the oportunity to get my hands on a 2.5 rs block dont know what year other than it is a sohc block, and also I can get a pair of dohc heads . My questions are this if I were to go with a 2.5 block swap would I need to replace the wiring harnis? I have looked around and found that this is major pain it the butt so would I have to swap the harnis. Also with the heads I need a new intake manifold and all the godies that come with that. Also would oil pump, water pump, and oil pan fit a 2.5 rs block? Finaly would my auto trans fit a 2.5rs block. I have a 94 NA auto that I am boosting a lot and will blow in matter of time. Well any advice about his swap would be most apreciated.

[The Scooby]

if the main engine connectors are the same then no you dont have to, but if they are different, which i dont think they are, then its just plug and play.

[napphappy]

Everything that is mechanical bolts up, i.e. water pump oil pan, transmission ect.

You will need the dohc intake mainfold. But you can use almost all of the sensors off the 94 intake. With the exception of maybe the fuel rails, im not sure.
You will want to use your existing harness and sensors.

The engine harness connectors are not the same.

[sammydafish]

Everything that is mechanical bolts up, i.e. water pump oil pan, transmission ect.

You will need the dohc intake mainfold. But you can use almost all of the sensors off the 94 intake. With the exception of maybe the fuel rails, im not sure.
You will want to use your existing harness and sensors.

The engine harness connectors are not the same.

yup, you just have to swap your harness onto the new manifold. you can even use the sensors that are in the DOHC manifold, the only exception is the IAC, but that depends on what kind you have. You might also have to swap on your TB, depending on year, the TPS changed and they bold on differently so you can't just swap the sensor. It should swap right over though. It's a pretty simple procedure.

I just did this swaping a MY00+ SOHN engine into a DOHC outback. The harness swaped right over, I had to use the TB and IAC that belonged to the car. Other that it just swapped right in. IAC mount was custom on this car becasue the 2.5 SOHC cars have a stepper motor IAC on the TB, but everything from 89-99 uses the same basic style of IAC, so you should have no problems.

[waldo320]

Will an 04 wrx intake manifold swap over to 99 legacy gt dohc heads, swaping out iac throttle body of course?

[sammydafish]

Will an 04 wrx intake manifold swap over to 99 legacy gt dohc heads, swaping out iac throttle body of course?

no, 04 should be the same bolt pattern as EJ25 SOHC heads with the offset pattern, 99 DOHC heads are inline and a little smaller. Plus the manifolds are about 8mm different in length.

[waldo320]

Well what manifolds should I look for then?? Also I found out the block is from a 99rs will the wireing still be the same as my car?

[sammydafish]

for a Phase 1 DOHC EJ25 you need a manifold off the same car, 96-99 EJ25 DOHC The bolts on the intake manifold will all be inline, as they should be on your heads. The runners are also a little more oval shaped.

[Matt Monson]

Any 89-98 Ej20 intake manifold will also fit. IAC won't be a problem, as they are the same, even though they are not in the same location. You will need to change the TB and TPS to use your '94. You will also want to use your '94 coil.

The one thing to keep in mind is that mating a phase II Ej25 bottom end to DOHC heads puts you right around 11:1 compression. This would be an NA build and not suited for keeping the turbo on your car. If you have your heart set on keeping the turbo, what you want to do is mate the DOHC Ej25 heads to the Ej22e block that's currently in the car. This gives you a compression ratio in the mid to high 8's...

I reiterate, since you seem worried about this: Everything mechanical bolts up. ALL Ej series blocks have the same size and shape and same mounting points for sensors. The block does not care about auto versus manual. They will all bolt up to all trannies. The heads are also very very similar with really only the intake manifold bolt pattern to address. As we have said you need any Ej20 manifold up to, but not including '99 or any USMD DOHC EJ25 manifold from a '96-99 vehicle...

[waldo320]

Yah I am looking at the block for 2.5 liter and I can get cheap forged pistons for it acording arias will put me around 8.3 compresion with sohc heads, so I would asume that would be even lower with dohc heads. Big turbo plans for this car !!