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engine build time 2.5 liter or 2.0 liter

Old Mar 14, 2011 | 09:35 PM
  #31  
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Originally Posted by Rob Day
Dazdavies - Am I right regarding the standard 2.5 bottom end being potentially unstable past 400bhp or thereabouts? I was considering this when I bought my last project car, and looked into putting a 2.5 STI Forrester engine in my 2002 STI, but was informed that 400bhp would be the limit, and even this would be pushing my luck?!?!? Obviously with the right aftermarket components its possible to push more, but then even the block in OEM form can be at risk beyond 500bhp?

Sorry for sounding thick, but when you believe all you read without having the knowledge or experience like yourself its all 'here-say'. Your motor is/was certainly proof in the pudding, and my dearest compliments to you.

It was a shame the last SSO was soaking as I would have like to have seen some better times, although despite the monsoon it was amazing to see the times you and many other were managing to plant down the 1/4.

Rob

PS, Scott - Im sure Dunx missed your info from the original thread, and yes im again 'under the impression' that a standard 6 speed box if not abused will take upto 550bhp, and maybe more.... I think I read someone pushing 603bhp.... Banny is running well over 500bhp on his 6 speed which is also a 2.0 STI lump if memory serves me correct?

Rob
Rob the standard pistons are p.iss poor on a 2.5 and will limit you to around 400bhp and 1.3bar boost. As oem I would not recommend pushing over 500 with forged components around 450ish seems to be a good realiable area for a standard 2.5 block.

I am running 523 on my 6 speed a friend was running 620bhp no issue on his 6 speed, a very durable box!

For a road car you cant beat a 2.5 with a MD turbo, here is one running just over 1.5 on a MD321T+ vvt heads newage



or a classic sti 5 on the same turbo at 1.8bar



And for those that say the 2.5 wont rev or feel brutal up, GT35/42R at 1.9 bar


Last edited by banny sti; Mar 14, 2011 at 09:43 PM.
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Old Mar 14, 2011 | 09:42 PM
  #32  
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Rob,

You're correct that the standard bottom end is good for 400bhp the weakness is the standard internals particularly the pistons. Fit new internals and the bottom end becomes good for 500 where the block then becomes the weakness. This is when pins are required.

When I do 2.5 builds for people they always have forged internals AND pins I just wont do it any other way now.

Cheers

Daz
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Old Mar 14, 2011 | 10:06 PM
  #33  
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2.5 Forged CDB, Race cams & a 35R would be niceee
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Old Mar 14, 2011 | 10:35 PM
  #34  
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Originally Posted by dazdavies
the block then becomes the weakness. This is when pins are required.
Daz
Daz, is this due to the thinner walls of the bores on the 2.5 blocks? I presume they are thinner due to piston size?

Si

Last edited by si2000; Mar 14, 2011 at 10:38 PM. Reason: grammar
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Old Mar 14, 2011 | 11:37 PM
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Yup exactly that. The liners are thinner on the 2.5 blocks
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