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Need advice - tuning STi 6 to 2.5l
View Poll Results: Which sub-assembly do you think i should use?
Go 2.5 litre but must be 2.5 STi crank etc. 2 100.00%
Go 2.5 litre, can use Forrester sub-assembly 0 0%
Use 2004> WRX 2.0 sub-assembly - later technology so should be fine 0 0%
Repair 2.0 STi 6 crank as this is the best of all these options 0 0%
Voters: 2. You may not vote on this poll

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Old 19 Aug 2007, 06:32 PM   #1 (permalink)
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Need advice - tuning STi 6 to 2.5l

Hi

I've been lurking on scoobynet for a while and came across this forum while doing a google search for some info.

This is my STi 6


Ok... so i've run a big end bearing on my STi ver 6 after having changed the turbo. Time for the motor to come apart.

Calling on suggestions from those who know a bit about Subarus. I'm quite tempted to go 2.5 Litre now that the engine has to come apart.

Considerations are:

How strong is a Forrester 2.5 sub-assembly? Will it stand up to 1 bar boost from the Air Research (Garrett) turbo that i'm going to be running? The turbo is medium sized, and i would say similar to a Mitsubishi TD05 20G turbo.

Or do i have to get a 2.5 STi sub-assembly?

If I stick with the 2.0 setup, i'm considering replacing my existing sub-assembly with a 2005 WRX sub. While the WRX sub is in the car, then i will rebuild the existing STi 6 sub-assembly (as the crank is supposed to be much stronger than modern WRX units). Is anybody aware of why the new technology 2.0 WRX sub may not be up to the task of 1.0 bar boost and 7,500 rpm? I have had conflicting reports... some say it can't handle that much rpm.. some say it can't handle that much boost... some say it will do just fine.

All other bits on the car are stock, except for the management system which a fully-programmable unit, and the turbo mentioned above.

anxious to get moving again

I've included a poll for you guys to say what you think i should do.. but please also give some iinformed comments.

thanks.

RAS
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Old 19 Aug 2007, 06:56 PM   #2 (permalink)
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whereabouts you based mate? Alan Jefferies in Plymouth are good if you`re near there
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Old 19 Aug 2007, 08:13 PM   #3 (permalink)
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Another thumbs up for AJ's Oh and 2.5 STi
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Old 21 Aug 2007, 11:18 AM   #4 (permalink)
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Quote:
Originally Posted by PeterUK300 View Post
Another thumbs up for AJ's Oh and 2.5 STi
??

Tiny - i'm actually in South East Africa so... But thanks for checking mate.

I've decided i'm going to stick with the 2.0 as i can't find a lot of positive info on the 2.5.
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Old 21 Aug 2007, 11:20 AM   #5 (permalink)
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tyhe 2.5's tend to support better out right power and torque, however they are a bit laggier than the 2.0
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Old 21 Aug 2007, 04:03 PM   #6 (permalink)
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huh? 2.5 laggier? i thought it was less laggier but can't rev up to 8,000rpm like the STi can..??
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Old 21 Aug 2007, 07:48 PM   #7 (permalink)
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Personally stick with the 2.0 as I think I hear lots of things about the 2.5 burning a bit of oil...

Besides, I'd stick with what works
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Old 22 Aug 2007, 07:09 AM   #8 (permalink)
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phil, no offence but if you drive a 2.5 with similiar mods to your 2.0, you'll never go back.................

2.5 will have less lag on the same mods/size turbo than equivalent 2.0 also - always make far more torque but generally slightly down on power on some of the smaller turbo's suited to the 2.0

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Old 22 Aug 2007, 04:54 PM   #9 (permalink)
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With some of the things I hear about them I wont ever want to drive them Alyn!! You know an oil lamp will burn oil, but a 2.5? Crikey... Not that much!!

I remember Bob telling me how much his 2.5 used, I dont think I'd ever go there
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Old 22 Aug 2007, 05:58 PM   #10 (permalink)
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2.0 with similiar mods will burn a little oil just the same..................
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Old 22 Aug 2007, 09:40 PM   #11 (permalink)
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I was hearing Alyn that they where using a litre of oil every 500 or 1000 miles, I cant remember which, think it was 1000 tho...

I dont put nearly a litre of oil in between services and thats about 5000 to 6000 miles!!
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Old 23 Aug 2007, 07:23 AM   #12 (permalink)
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perfectly normal for a modded engine, although part of it depends on how well you run it in

customers last spec M5 was on around 1-1.5ltrs /1000mile and perfectly fine by BMW stds
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Old 23 Aug 2007, 10:19 AM   #13 (permalink)
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WELL.. After much research on the various scooby forums, i've decided to stick with the 2.0 setup. i'm after an STi9 crank, as these seem to be the bomb.

My car is now running a T3 turbo .48 turbine A/R, .6 compressor A/R and hopefully going to stick on 1.0 bar boost. Gotech fuel management.

From what i've come across, there seems to be too many issues witht he 2.5. sure it is much more torquey.. but there are too many other issues.. oil being one of them.

Also thee 2.0 has been tuned to death, so all the research is done.

Will keep you guys posted.
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Old 23 Aug 2007, 11:32 AM   #14 (permalink)
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y only 1bar of boost?
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Old 23 Aug 2007, 12:42 PM   #15 (permalink)
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until i can get my hands on some 550cc injectors, i don't want to start boosting heavy..

Still have the standard 440cc. What sort of boost can i run safely on the standard 440cc's???
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