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Old 03-01-2011, 06:33 PM   #1
RTImotorsports
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Default EJ25 SOHC swap to EJ25 DOHC HELP!

Hi my car ( 2000 subaru impreza rs 2.5 SOHC 5 speed manual ) had sucked up water the other daya nd caused a connecting rod to bend. Now my friend has an 98' RS that im buying his motor. Now i have multiple question on thsi topic.

(98 and previous year ej25's were DOHC), correct me if im wrong please.
and 99'- 2001 were SOHC.

Questions:
1.) Seeing that i have a a SOHC ej25, i was wondering if it is possible for me to put in the 98' DOHC EJ25 motor in place of my SOHC EJ25 along with the DOHC EJ25 ECU.

2.) I will have the 98' DOHC EJ25 complete engine, ecu, and engine wiring harness. Will it be a plug and play situation or will i have to merge wires?

3.) Also, I do know that the EJ25 98' DOHC engines are run of a MAF senor vs the MAP sensor. Now would i be able to put my intake( which has the map sensor bolt up to) from the SOHC engine to the DOHC engine without any problem or am i forced to run the MAF sensor with the DOHC ECU and Motor?

4.) If im not able to swap it to DOHC, will i be able to use the DOHC ej25 block with my SOHC heads?

5.) And lastely, i want some opinions, should i do a DOHC swap or keep it SOHC. What are the advantages of having an engine ran by MAF sensors verse an engine ran with MAP sesnors and which one would you prefer?

Sorry for so many questions but i need some help here!

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Old 03-01-2011, 07:22 PM   #2
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You need to find a SOHC motor. The DOHC is more headache than it can possibly be worth, plus you add the DOHC head gasket issue to your car.
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Old 03-01-2011, 07:25 PM   #3
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DOHC gasket issue, whats the issue with the gaskets?
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Old 03-01-2011, 07:53 PM   #4
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to answer the head gasket issue yes the dohc 2.5l engines do have head gasket issues but subaru has made a multi layer HG now to fix that and if you do run the dohc you should run the dohc ecu as well as the MAF dont use the map

you should be able to use the block with the sohc heads and i cant really tell you if the compression ratio will be the same but it should


some of the advantages of useing map is looking for and intake is a heck of alot easier
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Old 03-01-2011, 08:02 PM   #5
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thankyou ditto151 i appreciate it a lot!
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Old 03-01-2011, 08:13 PM   #6
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im doing some what of the same think on my car i have the 98 dohc engine that i just put in on my 1993 impreza
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Old 03-01-2011, 08:19 PM   #7
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Quote:
Originally Posted by ditto151 View Post
to answer the head gasket issue yes the dohc 2.5l engines do have head gasket issues but subaru has made a multi layer HG now to fix that and if you do run the dohc you should run the dohc ecu as well as the MAF dont use the map

you should be able to use the block with the sohc heads and i cant really tell you if the compression ratio will be the same but it should


some of the advantages of useing map is looking for and intake is a heck of alot easier
The new gasket helps, but doesn't completely fix the issue.

More importantly, yes you'd have to do a full harness merge and use the '98 ECU (and I'm doubting it has the same connectors on the ECU side, so you need to come up with those) plus yes, you have to run the '98 MAF sensor intake. It would be much, much easier for you to either find a Phase 2 short block, or a complete SOHC motor from a wrecker.

You may be able to put the DOHC shortblock into your car complete, but I don't know what the compression ratio would be or if you'd have piston/valve conflicts.
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Old 03-01-2011, 08:22 PM   #8
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what other issue dose the head gaskets have
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Old 03-01-2011, 08:25 PM   #9
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and would ihave to run the harness from the firewall to the ecu itself from the 98 impreza and take out the harness out of my 00' impreza under the dahs and replace it with the 98'?
i have the engine harness where it connect to the two connectors on the left side of the motor is a brown and white connector
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Old 03-01-2011, 08:56 PM   #10
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Yes, you would have to merge the ECU plugs into your harness (if you can find them) and you would have to splice the EJ25D engine harness into your bulkhead harness at the firewall. You may even have to run additional wires and repin some connectors.

Or, you could skip the extremely difficult engine conversion that will hurt your peak torque numbers, and just get the correct shortblock. Heck, just replacing the rod and crank would probably be enough.
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Old 03-01-2011, 10:22 PM   #11
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Save yourself lots and lots of time and effort and frustration and just find another SOHC engine to install. There is no easy way to install the DOHC EJ25D in place of a SOHC EJ251/253. The ECUs are different, the harness connectors at the engine and at the ECU are different (so there's no easy way to swap the wiring), the sensor setups are different so you can't run the DOHC engine on the SOHC ECU, the Phase I engines have HG issues as already mentioned, etc. Subaru has sold hundreds of thousands of SOHC cars in the US since '99, so salvage engines just aren't that hard to find.

A simple search in this forum for "SOHC DOHC swap" would've given you the answers to all of your questions. I guess you were too busy triple posting your questions to bother searching.
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Old 03-01-2011, 10:26 PM   #12
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Well thankyou for the information, but are the ej251 and ej253 blocks the same and if i get an ej251 from a 2002 impreza will the block be the same? because i can only find an engine from a 2002 in the junkyards, theres nothing for 99'-01' around my area.
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Old 03-01-2011, 11:00 PM   #13
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Yes, an EJ251 from an 02 will fit your car and work as it was designed.

Swapping the shortblock is basically no harder than doing a headgasket job, with the added bits related to the oil pickup and pan if the new shortblock doesn't have them.

Jay
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Old 03-01-2011, 11:12 PM   #14
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Quote:
Originally Posted by RTImotorsports View Post
Well thankyou for the information, but are the ej251 and ej253 blocks the same and if i get an ej251 from a 2002 impreza will the block be the same? because i can only find an engine from a 2002 in the junkyards, theres nothing for 99'-01' around my area.
A 2002 block (or complete engine) would be excellent. You'd want to put your stock intake manifold under it but the longblock would be compatible.
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