originally posted by Kev from ScoobyClinic on www.M-Soc.com (midland scoobies)

The Gaffer, on 11 Feb 2014 - 11:21 AM, said:
Hi,

heres an example of what happens when using poor fuel..................




Can you see it ??



You can now, that’s what’s called a ring land failure and is due to detonation caused by poor quality fuel, eventually the broken bit rattles around, wearing the bore with debris until the engine is beyond repair, signs of this already show on the piston skirt.

The images shown are a piston from a 2.5 STI hatch that the owner admitted to running on 95 and sometimes 97 octane fuel, food for thought ......

cheers
kev

 

I think the Fuel issue is the source of ALL the ringland issues. (and thats why subaru couldnt work out what was going wrong) Pure speculation, but i wouldnt be surprised if most of the Franchised garages are putting regular through the super unleaded pumps and pocketing the 7p a litre (pays for their skiing hols).
A bit like all the pubs used to water the beer down. No one notices.
When Bob Rawle re mapped mine he said it can take 2 full tank loads before the ECU had caught up with the change. If you went from high octane to low octane the engine is going to detonate like hell for 500 miles shattering all those high silicone ringlands.
Ran mine on Sainsburys super unleaded for most of its life. But did run it on ordinary unleaded for 2 years when going up and down the M6 to scotland.
45k since new and still on same pistons.
Bob gave me a safe map back in 2008. I presume he set it not too advanced.

 

Certainly not the case with all Walsh128 although do agree perhaps 1-2.

Old days, pubs would water drinks down but newage we have Trading Standards etc all over the place thankfully and testing takes place in many pubs/stations.

It's a combination of many things - poor build of engine internals (fact), folk not having update remap, skipping the vpower & going for the cheaper unleaded versions either regularly or irregularly, driving it like the getaway car from the bank job every time it's started up....etc.

Any one of the above will put the car under the stress it isn't equipped to stand up too......although it really should.

Lets not forget though, many of these cars out there still going really well. Personally I've forged mind fully as didn't want to always drive the car with that worry always there each time I took it out a drive - but after buying a Subaru should I have had to budget on the additional £4.5k forge is the question.........

Hopefully on selling mine over the next year the forged engine and additional work on the baby will interest more folk.

 

I'm amazed that the slight difference in octane makes such a vast difference….

97 - all good

95 - curtains…

And that certainly doesn't seem right ? no failsafes ? no ecu auto adjustment ? looks like an accident waiting to happen….

NB coming from a 16k ring land failure, on a standard engine - looked after very well. Shafted by Subaru - so went to ET. Forged engine 40k miles ago and never looked back Now running a 'considered safe' 450 / 450 'isn.

 

The ecu should retard the ignition if it detects knock, all the 2.5's i've re-built havn't shown signs of knock/det and the fuelling has looked good. At the end of the day a standard car should have fuel ign parameters to a safe and reliable level. The 2.0 engine is very good and the only major mechanical difference is the pistons.

 

 

Yeah, but surely the ECU needs to detect det, then retard the ignition.
My understanding is that the piston rings are unable to tolerate any det.

 

Ive just thrown out a box full of 2.5 pistons the same or worse than these. My point is that det caused by poor fuel, too much ign advance, low fuel pressure, blocked injector etc would show signs of the problem on the piston crown. Either det marks or the piston crownstarting to burn away.
My opinion is that the pistons are just not good enough for the job, fuel etc may be part of the problem. But such a well developed engine should be built with enough 'head room' to cope with that, both mechanically and ecu wise.

 

Indeed - the pistons are not fit for purpose.

 

They are fit for purpose if you dont get detonation.
From what ive read. The piston to bore clearance is 1/2 thou of an inch (almost an interference fit) and to achieve this, the pistons are made with a high silicon content (hypereutectic. They expand at almost the same rate as the bore does as they heat up).
But this high silicon content makes them brittle, and thus susceptible to detonation. Turbos and superchargers add to the problem.
The closer you can get to the point of detonation, the better the efficiency.
the anti knock sensor adjusts the ignition timing to suit, so there should be no problem running it on 95 if you use that all the time. you just wont get the best power.
Forged pistons arent usually made from the high silicon alloy and so arent as brittle, but the piston to bore clearance is 4 or 5 times greater and thus the emissions are higher.

 

They're shyte

 

2.0 STI's are fitted with hypereutectic pistons, yes they run tight clearances, this in itself can cause problems with the them picking up in the bores if too much heat is generated. it's not a common problem but I've seen this as an issue as much as big end failure on 2.0 STI's.
However, 2.5 engines (WRX and STI) are fitted with cast pistons, not hypereutectic, well all the ones ive seen are, probably around 30 2.5 engines in the last few years.

 

Everyone else seems to think that they're hypereutectic in the 2.5 WRX and STi.

 

A hypereutectic piston is an internal combustion engine piston cast using a hypereutectic alloy............................


http://en.wikipedia.org/wiki/Hypereutectic_piston

 

Yes, cast hypereutectic aluminium alloy as opposed to cast aluminium.

 

Should have included..........

 

This has no doubt been covered in the 50 odd pages but are the previous shape hawkeye 2.5 engines much much stronger?

 

No, You have the added bonus of headgasket issues as well.

 

Oh FFS. I want my old car back then!

 

Get the engine forged by someone who knows what they're doing and the head gaskets bolted down with ARP studs. Provided you don't run silly boost through it you should be fine

 

If you look at a 2.5 piston, it has the same casting marks as a 2.0 wrx piston, nothing at like the HF/hypereutectic type 2.0 sti pistons.

 

I guess we will have to wait and see what the new engine does.
I suspect it'll have the inherent problem though.

 

Hi,

Im currently looking at options on getting my 330s fettled, upto 400/450.

What's involved in that (i.e do I need clutch etc) and what are the approx costs?

 

Well as a guide I'm running mine in now and should be getting 400 ish once properly remapped and this is what I got installed by API:
SC40 Turbo about £1k.
Ecutek remap £550.
New clutch £400.

Also refactor in labour and possibly forged pistons plus some other bits so could be another £3k quite easily.

I was advised by David to upgrade the brake pads when they need replacing but other than that the car can safely handle 400 or even 450 with a different turbo!

 

Can't agree with WMS about fuel being the issue. Many of my customers have owned there cars from new and have only ever run on Shell V Power or Tesco Momentun, which is every bit as good.

Almost every failure we have seen here, exactly the same as Kev shows in the pictures previously, are pistons 2 & 4. Fuel cannot select a cylinder that it doesn't like, so whilst it might be a contributory factor using low grade fuel. It is not the answer.

David APi

 

I never said fuel was the issue at all, I totally agree with you David. Someone else said fuel was the issue causing det. What I said was if that is the case the ecu should detect it and retard the ignition to safeguard the engine. I havn't seen any evidence that points to fuel being the issue.
I think the pistons are not fit for purpose. Why that is I'm not sure? But for a modern, well developed engine to suffer such a fundamental failure is beyond belief!!

 

Apologies too much info going in an old duffers ear.

BUT if the pistons are iffy why only the ones in 2 & 4?

 

Ive had a couple of engines with all 4 cracked on the ringlands. They do tend to be the rear cylinders though. Perhaps they are hotter running and the clearance is too tight? It's very random when they fail though, ive done a couple with less than 30K on them and some will go 80K and more with no issues?

 

Diesels the way forward xx

 

And no hatch diesel has blown up?