MY O3 STi has uprated internals
29 November 2002, 05:54 PM
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According to an article(www.autotrader.co.uk) that some guy put a link to here the JDM STi8 has an uprated crank,conrods and some special alloy pistons.Does this mean Subaru has finally tried to solve some of the inherent weaknesses with the engine.
29 November 2002, 06:12 PM
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Squeeza cast most probably, which is what accralite do I think. I think Accralite may have pioneered its use in pistons.
If you cast properly, and ensure no voids, then heat-treat, there's no reason why they can't be as strong as forged, or stronger still if the design is optimised.
Interesting claims have already been made about the sit7 engines durability.
Paul
If you cast properly, and ensure no voids, then heat-treat, there's no reason why they can't be as strong as forged, or stronger still if the design is optimised.
Interesting claims have already been made about the sit7 engines durability.
Paul
30 November 2002, 01:42 PM
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Interesting that these changes have been introduced now and not when the Sti7 was released.Excuse my mechanical ignorance but do any of these changes(if true!) mean that the 'bearing' that often fails on these cars is less likely to do so?
30 November 2002, 01:45 PM
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Was also wondering what implications the twin scroll turbo will have to tuning. Will it make the addition of aftermarket exhausts anymore problematic? Would a whole new generation of Ecutek,Link,Gems have to be developed to suit it?
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03 December 2002, 02:39 AM
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Did anyone else spot the crank trigger pattern on the STi VIII sprocket? That in one fell swoop could prevent the Link, MoTeC etc working with this engine until the software is updated. As for Tek3, I don't believe that there's an MY03 EcuTek version available yet, but see no reason that it shouldn't be possible 
With regard to internals... it is possible that the pistons are T6 hypereutectic, which would make them rather special, but still not as good as a proper forged piston... but hypereutectic pistons do have the advantages of cast items in so far as low thermal expansion (so less taper required, ie doesn't sound like a diesel when cold) and also good strength compared to conventional cast pistons. It's still no match for a good forged piston... when I see an engine making nine thousand BHP on a hypereutectic piston I'll accept them as an equal to good forged ones (which can and do make that kind of power).
With regard to the tuftriding, as already mentioned it's a case hardening process (gas / liquid salt bath). Quite why they've done this I fail to understand. It's not as effective as plasma (ion) nitiriding, but I suppose that it has a better yield and it's cheaper... but why go to the effort? The Subaru crank is a strong forged item, the only failure I've ever heard of was a unit that snapped within an engine delivering 450 lb/ft... the only instance I can think of when it would be beneficial would be in the event of a bearing picking up, in which case the engine needs a rebuild anyway, and this may save you from having to buy a new crank... hardly a huge issue, you'de want to clean the crank thoroughly before re-use anyway, a process which is rather involved, making it more cost effective to buy a new one.
Nitriding does have a place on high value billet cranks (EN40B / 4340 steel); I'm looking into getting one of these for my project engine, and if I were unlucky enough to have a bearing pick up I'de be rather annoyed if it shafted UKP 2000 worth of crank... I've seen total devastation of pistons, snapped conrods, punctured block, but the crank survived, a testament if ever there was one to the worth of a good nitrided crank.. but let's not confuse the STi VIII crank with one of these.
What's more troubling is that the STi VIII still seems to be using the stock conrods, which leave an awful lot to be desired. Don't get me wrong here, they're not a shoddy item as far as production rods go, but they're not a high performance item. My first engine expired when a conrod snapped and took the block with it. Suffice to say my current engine doesn't have these, instead I chose a billet set which are known to be good for at least 700 BHP.
Seems to me that they've filled the STi VIII engine with buzzwords rather than making a concerted engineering effort to improve the reliability of the STi engine.
Cheers,
Pat.
With regard to internals... it is possible that the pistons are T6 hypereutectic, which would make them rather special, but still not as good as a proper forged piston... but hypereutectic pistons do have the advantages of cast items in so far as low thermal expansion (so less taper required, ie doesn't sound like a diesel when cold) and also good strength compared to conventional cast pistons. It's still no match for a good forged piston... when I see an engine making nine thousand BHP on a hypereutectic piston I'll accept them as an equal to good forged ones (which can and do make that kind of power).
With regard to the tuftriding, as already mentioned it's a case hardening process (gas / liquid salt bath). Quite why they've done this I fail to understand. It's not as effective as plasma (ion) nitiriding, but I suppose that it has a better yield and it's cheaper... but why go to the effort? The Subaru crank is a strong forged item, the only failure I've ever heard of was a unit that snapped within an engine delivering 450 lb/ft... the only instance I can think of when it would be beneficial would be in the event of a bearing picking up, in which case the engine needs a rebuild anyway, and this may save you from having to buy a new crank... hardly a huge issue, you'de want to clean the crank thoroughly before re-use anyway, a process which is rather involved, making it more cost effective to buy a new one.
Nitriding does have a place on high value billet cranks (EN40B / 4340 steel); I'm looking into getting one of these for my project engine, and if I were unlucky enough to have a bearing pick up I'de be rather annoyed if it shafted UKP 2000 worth of crank... I've seen total devastation of pistons, snapped conrods, punctured block, but the crank survived, a testament if ever there was one to the worth of a good nitrided crank.. but let's not confuse the STi VIII crank with one of these.
What's more troubling is that the STi VIII still seems to be using the stock conrods, which leave an awful lot to be desired. Don't get me wrong here, they're not a shoddy item as far as production rods go, but they're not a high performance item. My first engine expired when a conrod snapped and took the block with it. Suffice to say my current engine doesn't have these, instead I chose a billet set which are known to be good for at least 700 BHP.
Seems to me that they've filled the STi VIII engine with buzzwords rather than making a concerted engineering effort to improve the reliability of the STi engine.
Cheers,
Pat.
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