Well these cars all have the same part number piston .. can't believe that the same part no covers different components. Not even Subaru could do that to themselves, they are an ISO9000 company when all said and done. So unless some oik is fitting the lower spec pistons when he should be fitting STi then they are all forged ... according to the parts book.

Part no's are 120006AB-310,320,330,340 and suit all STi 5/6 incl the S201 EJ207 engines. Part no 12006AB-230,240,250,260 and are fitted to WRX, WRXRA EJ207 engines, part no 12006AB-190,200,210,220 are fitted to EJ205 engines.

Hope that helps

[Edited by Bob Rawle - 7/5/2002 10:43:18 PM]

I was under the impression that the STi 5/6/P1 all had forged pistons, but am now told this is not the case.

Any more detailed info on this?

Thanks Bob.

I take it Dr banks is now looking for pistons, rods, fmic, gearbox etc etc etc etc

Just buy an STi5 and be done with it John! :D;)

Not all sti cars have forged pistons- when they a re ordered in japan there is a comprehensive order sheet that the customer fills in
It is possible ( though not that common )for someone to order standard pistons as we have seen here in New Zealand same goes for version 3 open and closed decks in a Type R
Bottom line it depended on the tick sheet
Regards

Options are endless, however its clear that forged pistons are standard fit and anything else is unusual, part no's are for the standard options ie forged where std and cast where std.
bob

How come all P1's don't have forged pistons then?

unless subaru uk on the 'tick sheet' did not tick the option of forged pistons?

Chris

How do youknow that P1's don't have forged pistons ? as I said the part numbers indicate they do. Do p1's run a reduced rev limit ie 7000 rpm ?

(just a hypothetical question as I know the answer)

Bob

I would go along with Bob but i thought this thread would be full of people who no there stuff.
Yes my P1 does revs to over 8000 rpm but only the once as i would like it in 1 x piece.

What pistons were fitted to STI4's.

Stronger Molybdenum coated pistons, unless specifically ordered when purchased from STI.

[Edited by submannz - 7/9/2002 2:09:22 AM]

[Edited by submannz - 7/9/2002 2:11:20 AM]

Bob,

have been to companies who have stripped several sti (all 5s) untouched from leaving the factory and they have found cast pistons inside them.

I find this hard to believe due to the 8000rpm rev limit, but there was no contesting it.

I believe mike at scoobymania has seen it before as have one other company who I cant remember on here who have delved into stripping sti 5s.

Wow! we live and learn.

Is the 8k rev ability to do with items being 'lightened and balanced' then?

They look like forged pistons well, why does everyone else think they are forged??? And if there are people saying that forged, was an option from the factory, how can NO STIS's have forged pistons?? The 'forged' pistons are completely different in design to 'cast' ones. Surely if they made the pistons a lot smaller, using the same material, they would be weaker, and less suitable for the high performance models? Even places like MRT sell them new as OE 'Forged' STI pistons, at considerable cost too.

Possibly squeeze cast pistons. Die cast when molten, followed by a little forging to work the material into shape.

Forged pistons (always used to) tend to be heavier, because of the limits of thin walls offered by the forging process.

I wouldn't be surprise that a cast piston with a longer skirt could be made as light as a short skirt forged item. As for strength who knows, casting alloys have come a long way.

Paul

Everybody thinks they are forged, cause they don't know what they are talking about. It is because Subaru and STI mention the word forged when referring to these pistons.

But it is the process they use to get the molybdenum on the pistons they forge the molybdenum onto the cast alloy piston.

Do a search on molybdenum and you can find out more.

So what about the forged pistons without a molybdenum coating?

The coating is to reduce friction, and forging it on? You must be reading the wrong thing.

For a start, the Molybdenum is actually Molybdenum Disulphide, as in the black grease you can get.

I am interested in exactly how you *know* the pistons to not be forged.

Eitherway, it has more to do with the fact that the pistons are physically smaller (shorter skirt) that makes them so different.

Paul

[Edited by Pavlo - 7/13/2002 7:38:04 PM]

Gents ... the "book" is pretty clear about the part numbers, Adam ... I'm sure that many people have seen cast pistons or forged pistons ... so you define what one looks like if you can as hearsay is just that. This discussion is valid, STi claim that forged pistons are used, Adam et al claim otherwise, I am inclined to quote what are presented as facts until I know otherwise but being "told" otherwise is not good enough for me I'm afraid. I good high pressure die casting will look very similar to a forging, only a grain structure analysis can be really definitive, Sti pistons are lighter and, the MY99 on at least are Molykoted on the slippers to reduce wear. Sti state forged, they may mean forged quality but even if that is so then forged quality is as good as forged is it not ? STi pistons are said to be not strong enough, that is as much to do with crown thickness as anything. Since STi pistons are lighter to cope with the increased re limit then either the quality of pressure die casting is b good or .... they are forged.

Perhaps we had all better type "forged" not forged for the time being. At the end of the day the whole issue is relative as anyone uprating an engine discards the oe items in any case.

horah, sense!

Anyway, back to the spirit of the thread....

I think that John wants to do the same as me, and what Stevie IS doing. And that is uprating the standard non-Sti pistons with something better.

Cosworth forged (as in smithe) pistons are nice, and expensive.

Sti pistons can be had for not much money, £240+vat for a set of used ones.

So does it seem reasonable to uprate an engine on a tight budget using Sti "forged" pistons. If so, what is the best compromise for limits on speed/power/torque.

Paul

On MY99 onwards the rods and crank are the same for STi as non-Sti (even on earlier models as well) so the main hindrance to increasing the rev limit is the piston, using an sti piston will allow higher rev limit and possibly a bit more boost but you will not gain much more than that, 1.3 bar (ish)is imho about tops for non STi cars, beyond that as far as STi's are concerned its down to the individual car and how it behaves against higher boost. Boost profile comes into play as well, 1.4 bar is "ok" up to say 4.5/5k (non Sti) but then it needs to be tapered down. Power is not all about boost, I view boost as torque and timing as power. If you can get both then wow !!

Thanks Bob, pretty much as I thought (after listening to plenty of others, I don't really *know* these things).

I am patiularly interested as I wan't to change the heads on my legacy to some versin of impreza, and need to do the pistons anyway.

So Sti pistons seem like the logical choice.

I would be careful say things like "you can run x.xx bar upto..." as it might come back to bite you!

Paul

Very interesting. I knew there was a bit more to it, and I hope the confusion many of us have had is starting to clear. Now what about an STi cam set into a UK car? What else would have to be changed (apart from the map :D )

The later Sti uses variable valve timing, probably the same as bmw, by skewing the shaft on a worm drive.

Piper cams do a range of 3 cams to fit the impreza, but the 2 you would probabl be intersted in need solid followers.

Paul

Heads are the same for both UK and STI, ergo they fit straight in (MY99-00) Cams are the other real difference.

Bob

you got any more info on the cams paul??? I fancy some lairy cams for mine...

David

when was it exactly that I became the font of all knowledge!?!?

I am currently torn between coilovers, brakes, and a head/piston swap. Should really wait a couple of weeks until I get paid.

Either way, I am looking to put some heads with cams on from something like an Sti 2, and get some forged pistons.

PS, my wife says she is gonna blow scoobynet up, just thought I would share that.

Paul

LOL Pavlo

paul you think youve got problems.. Im thinking of doing all of them... trouble is I should finish the first things.. :rolleyes:

David