Welcome to the North American Subaru Impreza Owners Club Thursday September 18, 2014
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Here you can view your subscribed threads, work with private messages and edit your profile and preferences Home Registration is free! Visit the NASIOC Store NASIOC Rules Search Find other members Frequently Asked Questions Calendar Archive NASIOC Upgrade Garage Logout
Go Back   NASIOC > NASIOC Technical > Normally Aspirated Powertrain

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads.
Reply
 
Thread Tools Display Modes
Old 07-31-2003, 06:39 PM   #1
marioej18
Scooby Newbie
 
Member#: 31115
Join Date: Dec 2002
Chapter/Region: Tri-State
Location: northeast PA
Vehicle:
2004 saab 9-3 aero
black

Default DOHC vs. SOHC

i was wondering if there are any performance differences between the DOHC ej25 and the SOHC ej25.....

which one is the better engine?
which one is more reliable?
which one is better for more performance, as in, which one is the better engine for getting the most power out of things like headers, ,intakes, cams, exhausts, pulleys, etc....?
* Registered users of the site do not see these ads.
marioej18 is offline   Reply With Quote
Old 07-31-2003, 06:43 PM   #2
White 2.5rs
Scooby Guru
 
Member#: 39936
Join Date: Jul 2003
Vehicle:
99RS TWE&SCAT EJ257
Hydra+HMist+PPG+35R=DEATH

Default

which one is the better engine?
which one is more reliable?
which one is better for more performance, as in, which one is the better engine for getting the most power out of things like headers, ,intakes, cams, exhausts, pulleys, etc....?


better, the sohc, subaru messed up making the dohc head gasket and/or head assembly, they are notorious for blowing head gaskets

dont know the answer to number 2, but im thinking the sohc, less rebuild time and such
White 2.5rs is offline   Reply With Quote
Old 07-31-2003, 07:02 PM   #3
JewPac42
Scooby Guru
 
Member#: 23260
Join Date: Aug 2002
Chapter/Region: BAIC
Location: -=3/1 Jew Crew=-
Vehicle:
Patr ick Willis
for Rookie of the year

Default

Lots of what I have heard depends on the mods. I think the DOHC was a lower compression engine which is why it takes to a turbo better then the newer SOHC engines. Aside from that Im not really sure.
JewPac42 is offline   Reply With Quote
Old 07-31-2003, 07:08 PM   #4
Julian
Scooby Specialist
 
Member#: 1182
Join Date: Mar 2000
Location: Ventura, CA
Vehicle:
MY00 RS
BRP

Default

Power ratings are the same for both motors. Most everyone agrees the later SOHC motors have a better 'area under the curve'.
Julian is offline   Reply With Quote
Old 07-31-2003, 07:28 PM   #5
Penphoe
Friendly Neighbourhood
Moderator
 
Member#: 269
Join Date: Sep 1999
Chapter/Region: VIC
Location: Burnaby, B.C., Canada
Vehicle:
2005 ABP LGT LTD BP6
00 Impreza RS GM6 RIP

Default

Quote:
Originally posted by Julian
Power ratings are the same for both motors. Most everyone agrees the later SOHC motors have a better 'area under the curve'.
Actually, the Phase-2 SOHC engine makes a tiny bit more power - 165hp and 167ft-lbs of torque. If memory serves me correct, the DOHC made 162ft-lbs of torque.

Whatever - the DOHC had a slightly higher rev-limit too!

LaterZ!
Darren!!
Penphoe is offline   Reply With Quote
Old 08-01-2003, 08:10 AM   #6
MY99 2.5GT
Scooby Specialist
 
Member#: 5030
Join Date: Mar 2001
Chapter/Region: MAIC
Location: Martinsburg, WV, USA
Vehicle:
1999 Legacy 2.5GT
05 Legacy GT 06 Armada

Default

Phase I (DOHC) Motor = Notorious for blowing head gaskets due to a miss positioning of the crank mains which allowed the crank to teater slightly, and I mean very slightly. This weakened the gaskets over time. Subaru also recocgnised a problem with the manufacturing of their head gaskets. Simply put they put crappy gaskets in the pre 2000 motors. The DOHC heads are still deemed more tunable by the likes of COBB and old school tuner Mike Shields. 6500rpm redline

Phase II (SOHC) Motor = Made slightly more power and favored by most subaru owners because the fact is its twice as expensive to buy performance cams for the DOHC. 6250 redline

Both of these heads are capable of about 8000 rpm before you really risk float.

Brad
MY99 2.5GT is offline   Reply With Quote
Old 08-01-2003, 09:52 AM   #7
IggDawg
Celebrity Guest Star
 
Member#: 10648
Join Date: Sep 2001
Chapter/Region: NESIC
Location: Sort of Boston, MA
Vehicle:
2002 Escort... D:
Mostly kind of white

Default

unless I'm mistaken, the reason they went to SOHC instead of revising their DOHC design was for performance. in most DOHC 4 cylinder engines, you have 2 camshafts. in the boxer engine, you have 4. they aren't quite half the length of an inline camshaft so you end up with much more rotating mass. on the NA engine, that's not good. with the turbo engine, it's not so much an issue. dial in .01 PSI more boost, and you've overcome the issue. an NA engine is built on maximizing power loss from every place you can.

-IggDawg
IggDawg is offline   Reply With Quote
Old 08-01-2003, 11:29 AM   #8
Jademonkey
Scooby Specialist
 
Member#: 9213
Join Date: Aug 2001
Location: My grandma was 6' 6"
Vehicle:
2000 RS
Red

Default

Quote:
Originally posted by MY99 2.5GT

Both of these heads are capable of about 8000 rpm before you really risk float.

Brad
Unless you have luck like me....
Jademonkey is offline   Reply With Quote
Old 08-01-2003, 11:33 AM   #9
IggDawg
Celebrity Guest Star
 
Member#: 10648
Join Date: Sep 2001
Chapter/Region: NESIC
Location: Sort of Boston, MA
Vehicle:
2002 Escort... D:
Mostly kind of white

Default

I've heard that the EJ25 is good till around 7000 RPMs bone stock. any truth to that?

-IggDawg
IggDawg is offline   Reply With Quote
Old 08-01-2003, 02:05 PM   #10
Farfrumwork
Scooby Newbie
 
Member#: 10202
Join Date: Sep 2001
Chapter/Region: RMIC
Location: Louisville, CO
Vehicle:
'07 Spec B
'85 EJ25 Syncro Westy

Default

It seems as though the DOHC is more prone to headgasket failure... but I don't think the cause has been nailed down - I, for one, believe that it was mostly the gasket design/vendor that caused the trouble.

SOHC's have blown HG's too - just not as many/unit sold (I have to concrete data on either...)

I can say this though - the SOHC has ~15ftlbs more torque below 5000rpm than the DOHC. The DOHC has ~10ftlbs more 5200-5700 and ~15ftlbs more from there to redline. I have a dyno from Pat O. but I dopn't know how to post it... and, as stated, the DOHC has a 6450rpm redline

so, "on the boil" the DOHC should edge out the SOHC, but a set of cams on the SOHC will change that. and cams for the dually are 2X the cost of the singles. The SOHC has much better part throttle power/response due to the geometry of the rocker arms vs. shim over bucket of the DOHC.

I have the DOHC in me GT but I think a camed SOHC would be beter (unless I could get cam gears for mine and have it tuned.... that would be cool )

later
chad
Farfrumwork is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
EJ25 DOHC vs SOHC short block questions mattvct Normally Aspirated Powertrain 6 02-17-2009 01:41 PM
dohc vs sohc vs phase I vs phase II spdracr00 Normally Aspirated Powertrain 3 01-23-2006 02:53 PM
RS DOHC vs SOHC heads Unsung Boxer Normally Aspirated with bolt-on Forced Induction Powertrain 31 09-12-2005 03:49 PM
Iridium spark plug DOHC vs SOHC Theory yebokmj Normally Aspirated with bolt-on Forced Induction Powertrain 9 05-09-2003 07:56 AM
Let's start the DOHC vs SOHC ALL over again ;) jetfreak Normally Aspirated Powertrain 8 03-17-2001 10:31 AM


All times are GMT -4. The time now is 11:05 PM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2014 Axivo Inc.
Copyright ©1999 - 2014, North American Subaru Impreza Owners Club, Inc.