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Old 04-04-2005, 04:29 AM   #1
kickitjp
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Default What's the diff between DOHC EJ25 and SOHC

What's the difference between the DOHC EJ25 (98 RS) and the SOHC (99+ RS)?

...obviously one is dual and the other is single...but what else?
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Old 04-04-2005, 04:35 AM   #2
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http://forums.nasioc.com/forums/show...ight=dohc+sohc

You should find you anwser somewhere here
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Old 04-04-2005, 04:47 AM   #3
kickitjp
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Thanks for the crosslink, but I was the #6 poster in that thread and no it does not answer my question.

What I'm really trying to find out is why Subaru made the EJ25 in a MY98 RS a
DOHC engine, and all years after that a SOHC EJ25?

Are we seeing any performance differences?
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Old 04-04-2005, 09:52 AM   #4
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I know you guys know bump.
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Old 04-04-2005, 11:11 AM   #5
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kickitjp - one of the main reason for the switch from DOHC to SOHC for the EJ25 was due to the fact that the SOHC is slightly lighter weight, and offered more mid-range torque compared to the EJ25 DOHC motor. The EJ25 DOHC's tend to make more power higher up in the rev band.
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Old 04-04-2005, 12:56 PM   #6
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You the man. Thanks!
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Old 04-04-2005, 10:28 PM   #7
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I read in the faq that the DOHC was "stronger" and the SOHC was "weaker". Are we talking about the crank, block or what? What is going to react better to mods and which engine is recommended?
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Old 04-05-2005, 04:47 PM   #8
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Actually, cstratton, I've always read the opposite: that the DOHC engine had some reliability issues, thus they switched (back) to SOHC.

Now I'm sure that's not the whole reason, but...........
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Old 04-05-2005, 08:52 PM   #9
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In the faq it says:
" DOHC 2.5L MAF Based (very strong)"
"change SOHC 2.5L MAF Based (very weak)"
Reliability could be different from engine strength though, so that may be the reason.
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Old 04-05-2005, 09:32 PM   #10
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Default Some data.

The weak / strong reference on the FAQ is about the MAF sensor those engines used and their tendency to break or not. It doesn't refer to the block.
The SOHC engine offers:
- More torque at part throttle
- More mid end torque
- Higher torque peak (by 4 ft/lbs)
- Less components, lower weight, easier to manufacture.
DOHC offers:
- HP doesn't drop off as fast after it peaks.

1998 DOHC Engine:
Horsepower: 165 @ 5600 pm
Torque: 162 @ 4000 rpm

1999 SOHC Engine:
Horsepower: 165HP @ 5600 RPM
Torque: 166ft/lbs @ 4000RPM

Last edited by powerlabs; 04-06-2005 at 05:05 PM. Reason: Pulled up some numbers for both engines.
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Old 04-05-2005, 09:47 PM   #11
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Quote:
Originally Posted by GTBGUY
kickitjp - one of the main reason for the switch from DOHC to SOHC for the EJ25 was due to the fact that the SOHC is slightly lighter weight, and offered more mid-range torque compared to the EJ25 DOHC motor. The EJ25 DOHC's tend to make more power higher up in the rev band.
that is waht i was going to say, also one has one cam SOHC and the other has two cams DOHC..
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Old 04-05-2005, 10:53 PM   #12
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i have a 99 rs with the sohc motor and was wondering if the it would be better performance wise to get a set of dohc heads on it. in a NA performance build up would that be better?
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Old 04-05-2005, 11:56 PM   #13
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Quote:
Originally Posted by powerlabs
The weak / strong reference on the FAQ is about the MAF sensor those engines used and their tendency to break or not. It doesn't refer to the block.
The SOHC engine offers:
- More torque at part throttle
- More mid end torque
- Higher torque peak (by 1 ft/lbs)
- Less components, lower weight, easier to manufacture.
DOHC offers:
- HP peaks at a higher RPM and doesn't drop off as fast.
exactly! cheaper to produce is a large reason they switched over. THey could make the engine perform better and feel more powerful for cheaper.
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Old 04-06-2005, 01:58 AM   #14
kickitjp
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Thanks for the answers.
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Old 04-06-2005, 04:35 PM   #15
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So the DOHC, powerwise, is actually better? And what's this about it being "stronger?" When we say strong, we mean mechanically, right? We're not counting the crappy head gaskets?
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Old 04-06-2005, 05:04 PM   #16
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Quote:
Originally Posted by Al_Smokemcrack
So the DOHC, powerwise, is actually better? And what's this about it being "stronger?" When we say strong, we mean mechanically, right? We're not counting the crappy head gaskets?
Did you bother to read my response?
Quote:
Originally Posted by Powerlabs
The weak / strong reference on the FAQ is about the MAF sensor those engines used and their tendency to break or not. It doesn't refer to the block.
1998 DOHC Engine:
Horsepower: 165 @ 5600 pm
Torque: 162 @ 4000 rpm

1999 SOHC Engine:
Horsepower: 165HP @ 5600 RPM
Torque: 166ft/lbs @ 4000RPM
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Old 04-06-2005, 09:32 PM   #17
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Ooooooh. I'm sorry. I must have skipped right over that one.
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Old 04-06-2005, 10:34 PM   #18
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Quote:
Originally Posted by Hawk296
exactly! cheaper to produce is a large reason they switched over. THey could make the engine perform better and feel more powerful for cheaper.
Not only is it cheaper to produce, its also cheaper to maintaince as there are less parts to it than DOHC
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Old 04-07-2005, 12:40 AM   #19
Al_Smokemcrack
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And no stupid shims! Yay easy to adjust valvetrain!
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