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Old 05-09-2003, 09:51 AM   #1
ShzSTi
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Default 2.0 STi vs. 2.5 STi motor

so which one is better?
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Old 05-09-2003, 11:24 AM   #2
Austin
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2.5
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Old 05-09-2003, 11:46 AM   #3
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The 2.0 is a time tested design. The 2.5 has 25% more displacement. You be the judge.

I, for one, can't wait for the 2.5 to be put in the Legacy!
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Old 05-09-2003, 11:54 AM   #4
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where are you... what are you running for gas... what do you want out of it....

im staying with a 2.0 or a 2.2 for my daly driver, and a 2.5 for my sleeper L wagon... why? no reason.. just becasue.
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Old 05-09-2003, 12:46 PM   #5
STEALTH-WRX
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2.5 all the way. then you can build it to a 2.8. those are my next plans after i am bored with this motor.
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Old 05-09-2003, 06:10 PM   #6
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What about a 3 litre 6 cyl H6 Outback engine..they are only 20mm longer the the 4cyl..and they will fit into the WRX engine bay..

Rebuild the H6 to suit turbo application add a nice turbo and ECU.

That would be a weapon

OzWRX
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Old 05-09-2003, 07:56 PM   #7
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There is no way to compare a newly designed motor with one that has been around for years. The only thing you can say is the 2.5 has more displacement, everything else is speculation. After people start modding and beating on the 2.5 we will find out how strong it is.

On another note, I have heard reliable rumors, if there is such a thing. That the legacy will have a turbo 3.0 H6 in a couple of years. Who knows if that will actually happen or not, but it would be pretty sweet.
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Old 05-10-2003, 03:00 AM   #8
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Interesting, I've heard the Legacy will carry over the 2.5L STi's turbo engine, tuned a little differently of course.
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Old 05-10-2003, 05:01 AM   #9
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Default Heard the same

from my friend who works for Subaru.

San
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Old 05-10-2003, 03:05 PM   #10
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We dont know yet. Thats the correct answer. We will have our STI in just 2 short weeks. When it arrives and after a few months of tuning we will have a better idea.

Facts right now:

In current motors going to a 2.5 is a backwards step due to the head castings. Major head work is needed to make the added displacement worth while. If the 2.5 uses the same STi head castings this new motor "might" not be the best thing since sliced bread.

The 2.5 STi is a US only motor and that scares the hell out of me. Japan still gets the 2.0's.

A 2.0 that spins to 8500 rpm with a short stroke and lighter rotating mass has a much higher power potential then a 2.5 ltr motor with long stroke and heavy rotating mass that is limited to 7k rpms. The new 2.5 has the writing on the wall to be that motor. Man I hope its a gem and thats all we can do right now is hope.

Its clear that Subaru gave us the 2.5ltr in the STI because they had to. 91 octane fuel really limits the power you can make with forced induction and as a result the turned to displacement to get the power to compete with the EVO.

CT
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Old 05-10-2003, 03:57 PM   #11
MJU1983
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clark-

in terms of modding.. which is a better purchase? the 4G63 EVO or the 2.5 USDM sti? i think the EVO is the better choice what do u think?

thanks

-mike
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Old 05-10-2003, 05:12 PM   #12
Yungimoto
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Quote:
Originally posted by MJU1983
clark-

in terms of modding.. which is a better purchase? the 4G63 EVO or the 2.5 USDM sti? i think the EVO is the better choice what do u think?

thanks

-mike
4g63 is a proven engine.... as was said before no one knows what the 2.5 can do yet.
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Old 05-10-2003, 06:06 PM   #13
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ya well... so it the ford big blocks but that doesnt mean there not out dated.
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Old 05-10-2003, 10:25 PM   #14
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Quote:
Originally posted by totoherbs
ya well... so it the ford big blocks but that doesnt mean there not out dated.
The 4G63 is outdated? You think that a 2 liter motor that can push over 400 hp on stock internals is outdated? Ok if its outdated name a better 4 cylinder motor. The EJ20 is a great motor, but so far no one has proven its as strong as the 4G63.
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Old 05-11-2003, 10:07 AM   #15
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I love the R/S Rod stroke ratio of the EJ20s, it is ultimately better for power production and reliability at high hp levels. But the 2.5 should be just fine for a street or race motor. Neither is better, both represent two combinations of compromises. Some parts won't cross over as well as others.

Why is a longer rod set up better? The better r/s ratios produces lower piston speeds=Less cylinder side loading, Cooler running,cooler combustion temps(Run more timing Scotty!).
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Old 05-11-2003, 10:16 AM   #16
Jerry Hong
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The turbo EJ25 is almost eh same as the NA 2.5 except for stonger webs, and semi decking.. the fisical size of an ej25 is the same as an ej20.. the new EJ25 is just stronger for boosting.. how can you bore a 2.5 to a 2.8???? or better yet.. why??? the most people do is a 2.6..

jerry
www.twr-racing.com
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Old 05-11-2003, 07:58 PM   #17
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Quote:
Originally posted by AZScoobie
Its clear that Subaru gave us the 2.5ltr in the STI because they had to. 91 octane fuel really limits the power you can make with forced induction and as a result the turned to displacement to get the power to compete with the EVO.

CT
This is exactly the case: remember that the Evo is getting knock right off the boat in California, and that's with 180whp (shiv's dyno - WRXs tend to hit around 160). Displacement is a very easy way to make more power - if two engines have different displacement but are otherwise the same making and making the same amount of power the one with more displacement is going to be less stressed. There are exceptions, but generally this is correct.

When a 2L turbo motor is getting knock on Cali gas only pushing 273hp, you either need to get that state some better gas or up the displacement if you want more reliable push

I think that should tell you about the 4G63: it's going to be easier to make more power on the STi's 2.5L. Whether or not the strength of the engine can hold it is another matter, but somehow I've got a good feeling about the STi engine...
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Old 05-11-2003, 09:39 PM   #18
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Quote:
Originally posted by MJU1983
clark-

in terms of modding.. which is a better purchase? the 4G63 EVO or the 2.5 USDM sti? i think the EVO is the better choice what do u think?

thanks

-mike
We dont know. I am like the others. I hope and pray the STi2.5 is the engine to beat. 4G63's have been around for a while. We all know what they can do. I dont think people are going to get much more out of the EVo's then they did the older 4G63's. I think history will repeat itself on turbos used and times run with the eclipse and Talon.

CT
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Old 05-11-2003, 10:44 PM   #19
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I hear that the 4g63 has a problem with "crank walk". How does that factor in, considering we don't know for sure what problems arise in the STi's EJ25T?

Chris
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Old 05-11-2003, 10:52 PM   #20
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Quote:
Originally posted by AEA-1919
I hear that the 4g63 has a problem with "crank walk". How does that factor in, considering we don't know for sure what problems arise in the STi's EJ25T?

Chris
Chris, The older 4g63 motors did not have this problem. Only the newer versions in the later eclipse. This issue was supposed to be fixed with the EVO's updated engine. Time will tell.

CT
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Old 05-12-2003, 12:39 AM   #21
slim speedy
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Quote:
Originally posted by AZScoobie


I dont think people are going to get much more out of the EVo's then they did the older 4G63's. I think history will repeat itself on turbos used and times run with the eclipse and Talon.

CT
Oh well that sucks... I guess there will be a bunch of 9 second Evo's around then. Pretty damn slow huh?
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Old 05-12-2003, 01:24 AM   #22
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Quote:
Originally posted by slim speedy


Oh well that sucks... I guess there will be a bunch of 9 second Evo's around then. Pretty damn slow huh?
I would hope so. Thats been done 10 times over.

CT
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Old 05-12-2003, 02:51 AM   #23
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Maybe we should declare Cali it's own country. Then they can have all there detuned, water/gas cars. Then the rest of us can get the good cars that can run crazy power on 94 octane. Sounds good to me. Let's take a vote. Call your congressman!
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Old 05-12-2003, 04:14 AM   #24
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400hp on stock internals? I know the 4g63 is a strong engine, but didn't the EVO VII and VI have forged pistons? I know the US Evolution has cast pistons, and running 19psi on cast internals it seems like a pretty high state of tune. After cleaning up the fuel map and holding full boost to redline I'm sure the EVO will have more power than the stock STI, but in my opinion after similar tuning on the 2.5, it will yield a healthy increase in power. I think with equal mods the EVO will just be a step behind due mainly to the displacement of the STI engine.

I'm curious to find out what difference there will be changing the massive downpipe cat for a catless version! (The WRX has a 2L downpipe cat and the STI has no cat in the up-pipe so the downpipe has a 3L one!)
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Old 05-12-2003, 09:47 AM   #25
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Quote:
Originally posted by AZScoobie

Facts right now:

In current motors going to a 2.5 is a backwards step due to the head castings. Major head work is needed to make the added displacement worth while. If the 2.5 uses the same STi head castings this new motor "might" not be the best thing since sliced bread.

CT
Can you elaborate on the above statement and be more specific?!?

As this thread seems to be moving into an Evo vs. STI thread with regard to ultimate hp after modding, there is no doubt in my mind that the Evo with the right gas and pistons has ultimately more power potential due to its cast iron block. Remember the old 4 cyl BMW cast iron block in Formula 1! I don't believe that the Subaru blocj has the same strenght for ultimate boost. But I also suspect that it will always be the nicer street engine for the fuel we have here.
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