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Old 11-15-2001, 03:27 AM   #1
Stroke
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Default questions on dohc 2.5

i'm sure you've all heard these questions before, but i'm a newbie so bare with me. i have a 98 RS and i was wondering why if i have dohc, as opposed to every other year RS with sohc, that i have the same factory rated horse power? exactly what are the differences? (aside from having more cams )
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Old 11-15-2001, 03:31 AM   #2
Eric SS
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Yes you have DOHC. the SOHC started in 1999. You have the same horsepower but 2 lb/ft less torque (164 vs. 166) but big deal. there are a lot of other differences (Copmbustion chamber size, piston design, compression ratio) but I don't know all the numbers off the top of my head.

And last, if you own a 1998, You had better say that you just bought it so I know that you haven;t owned it for a while and just discovered our wonderful club!

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Old 11-15-2001, 03:45 AM   #3
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yes, yes. i bought the car in april, and i've known about the club for a while, but i've been learning new things about the car all along. i didn't know jack about cars until i bought one worth talking about
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Old 11-15-2001, 03:59 AM   #4
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Old 11-15-2001, 04:04 AM   #5
Stroke
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ha ha.. ok. ya got me. i was in a hurry, ok! sorry...
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Old 11-15-2001, 04:04 AM   #6
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*cough*took longer to post and wait than search*cough*
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Old 11-15-2001, 04:07 AM   #7
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"search rules!!"
LOL, thats a new twist.
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Old 11-15-2001, 04:11 AM   #8
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ok, ok. i understand that searching is always a good route to take to keep from bothering people that have just SOOO little free time but did you read the link? told me nothing i don't already know. just wondering if there's anything else to my engine.
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Old 11-15-2001, 02:40 PM   #9
bsquare
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Other than the heads, the 98 and 99 engines (please, no MAS/MAF comments) are the same. You have the same power ratings because the heads flow the same in this application, and the other engine parameters are the same.

The thread I posted made clear the (minimal) differences. Perhaps you were just expecting there to be a lot more than there is.


Ben
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Old 11-15-2001, 04:53 PM   #10
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ok Ben, thanks for your input. answered my question
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Old 11-16-2001, 03:19 PM   #11
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98 imprezas kic a s s but the bumper sucks a * *
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Old 11-16-2001, 06:08 PM   #12
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yes, yes they do. in fact, i have a 99 bumper
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Old 11-16-2001, 06:49 PM   #13
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eh... dont all (or most) 98s have the phase 1 block whereas 99 sand up all have the same phase 2 block, except for a few 98s with phase 1 heads (the dohc) and phase 2 blocks since they adopted the design before the end of the model year? or is this whole thing just a figment of my imagination? i mean... assuming there are different combustion chamber sizes and whanot like someone said, the block had to have been changed right? unless it's just the curvature of the top of the cylinder (heads), which i doubt.
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Old 11-16-2001, 08:44 PM   #14
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There are no changes in the cylinder sizes or head displacement. The change was in the piston CR. The phase 1 heads on a phase 2 block are referred to as phase 1.5 engines.


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Old 11-16-2001, 09:22 PM   #15
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It's worth noting that the output of the two generations of 2.5L engines is not the same. Sure the peak numbers are the same (or very close to being the same), but the SOHC 2.5L has a significantly broader torque band than the DOHC 2.5L. Kind of counter-intuitive, as you would expect the DOHC to have better flow potential throughout the rev range, but apparently the redesigned SOHC heads are actually better in that respect. Having ridden in DOHC and SOHC cars, I think the added low- and mid-range punch is quite noticeable, particularly at part throttle.

Pat Olsen
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Old 11-17-2001, 12:55 AM   #16
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ok, but whether or not the sizes changed, they are different designs and thus makes another difference between the engines, which is what he is asking for.

they=the blocks, in case the ambiguous pronoun reference confuses anyone

Last edited by elemental; 11-17-2001 at 01:59 AM.
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Old 11-17-2001, 01:00 AM   #17
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Another difference? That is all anyone has said since the beginning of this thread!
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Old 11-17-2001, 01:57 AM   #18
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are you sure? read it again?

Quote:
Other than the heads, the 98 and 99 engines (please, no MAS/MAF comments) are the same.
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Old 11-17-2001, 02:54 AM   #19
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I'm sure you changed your post which I thought was referring to the heads, but you actually meant the blocks.
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