vulnax999

iTrader: (7)

A leak of information ... !

richgreenscooby1

iTrader: (2)

Hi mate ,

How have you got on, send me your reg number I want to check something on subaru system for you ..

chet123

iTrader: (7)

how did the engine failures occur on these models? are we saying the 330s are fine if kept on standard power until it is increased, or particular modifications are done which cause the failures. Is there a safe power ban or its imperative a forged engine is neccessary if changing turbo, mapping etc

thenewgalaxy

My understanding. If someone with relevant experience and qualifications spots a problem please correct me as I am just a keen enthusiast not an engine builder.

The commonly seen problem is with the pistons and head gaskets. The pistons are known to break and the head gaskets known to lift.

Two common criticisms are that the cast "hypereutectic" pistons are not up to the job and that the head gaskets are not bolted down tightly or strongly enough.

There have been reports of other failures on various components of the oil pump and turbo housing also, but these are not engine internals if you get my drift.

I have yet to see anyone definitively state what the cause is, but the generic OEM map is often criticised. It is believed that the engine can run lean under some conditions and that causes premature detonation. This can cause the pistons to crack as under these conditions they can be quite brittle.

Another suggestion is that the fuel pipe runs too close to hot components of the engine and in turn causes the fuel to run lean.

And another is that the pistons simply aren't up to the temperatures involved and for that reason they break, or even melt. Other suggestions include vibration through the engine and the way in which people drive them and tune the engines beyond the power they were designed to handle safely.

I have seen it commonly suggested that the head gaskets themselves are strong enough but the studs used to hold them down are in some way inadequate. Whether or not the factory doesn't do them up tightly enough, cannot do them up tightly enough or simply uses weak ones is difficult to say with much certainty.

We know a few things...

1. Some 2.5s have failed after a handful of miles
2. Some 2.5s are going strong after hundreds of thousands of miles
3. The problem is noticed in all 2.5 turbos from the blob USDM to even JDM hatch STis (some are fitted with this engine)
4. It is difficult to get rates of failures
5. Anecdotally it would appear that the 340r cars are less likely to go
6. The Prodrive and OEM 300 maps appear to have seen the highest rate of failure
7. Custom maps with a sensible power output appear to reduce the rate of failure
8. IM Group "Subaru UK" have upset an awful lot of their customers with their handling of this issue
9. A set of forged pistons (eg Mahle, Omega, Cosworth) and head gaskets (OEM or Cosworth) bolted down with something more heavy duty (eg ARP, Cosworth) appear to be a permanent solution
10. Forged builds are recommended to have a set of forged bearings also, and other components may be recommended also
11. When it was decided that "Subaru UK" wanted a headline figure halo model comparable to the FQ400 Evo they didn't just forge a couple of bits, they gave it to Cosworth who went mental then dialled it back to run it at a more conservative output

Edit - 12. Abuse of any engine can cause a failure, there is a common misconception that forged engines and twinscroll engines are "bulletproof" but the JDM cars run cast pistons also, neither do well if poorly maintained. It is crucial that oil and filters are changed regularly on high specific output engines.

Edit - 13. We do not use the STi twinscroll engines here for emissions reasons, some people wonder why we are landed with the "inferior" engine. (However some wonder why we don't have the S-GT engine).

Edit - 14. There are still issues with the thin walls of the block, these are still known to go in forged 2.5 engines. It is not advisable to run high boost through them. There are differences in opinion between the very best tuners as to the worth of pinning blocks, closed deck block inserts ("destroker kits") or just running a well mapped and balanced engine in terms of reliability.

If you want to push much beyond 350bhp you are looking at a lot of work and should really think about going for 450-500bhp if you want to make it cost effective. However a forged 2.5 is an utterly glorious engine for the road,.

Edit - mapped properly with more torque a forged engine is better than the stock 2.5 (which, if it didn't have these problems I know everyone would be raving about).

Would I touch a stock 2.5? As I have been bitten I would only buy forged from a good specialist or buy with the intention of forging - unless a 2.0 equivalent was available.

It is a shame because the hatch and Hawkeye cars now have a stigma attached to them but they are utterly fantastic cars. As these cars were built to be tuned I suggest anyone go ahead and make these engines what they should have been to begin with.

Edit - there are plenty of forged hatches from well respected specialists available. These are the cars people after a hatch should go for but they command a premium. Cosworth's forged OEM alternative is still very pricey but a brilliant machine.

Cpt Jack Sparrow

iTrader: (14)

^^^ Best post I have read in a while on this subject...

chet123

iTrader: (7)

thanks, i agree they are great cars, less agreesive looking than the blobs, bugs and classics, but not such good in the engine compartment. ashame

MOTORS S GT

iTrader: (2)

Don't think your Cosworth 2.5 engined machines are exempt from failure, as there have been a few fail now, but kept very quiet by IM.

APIDavid

iTrader: (4)

Addenda to a very thorough post by New Galaxy

* The cracked pistons syndrome is - in my experience - only ever cylinders 2 & 4.
** They also crack the oil pick up strainer ***** Nilly for no obvious reason.

I theorise that the stretchy head bolts are losing grip, tension, call it what you like through " block wobble ". The 2.5 has a very thin liner and the block flexes in use like a fiddlers elbow doing a polka. I suspect that the flex is causing further stretch and loosening of the head bolts, for the same reason that the head gaskets "creep". We never bother to check the undo torque of the head bolts when we take them out. Where is the point?, the damage is done and we aren't re-using them anyway.

Maybe they aren't lubed properly in first fit?, either under the bolt head or the threads and they aren't torqued properly through excess friction?

The list of possibilities goes on and on.

My opinion is that a stitch in time is the best option. They 'all ' do it, step in and do the job Subaru ought to have done properly - before it escalates.

David APi

thenewgalaxy

I recently became aware of a high mileage failure in one of the prototypes where a piston cracked but there was no further engine damage.

Have you repaired any at a Finch?

If Cosworth can't get it right then it doesn't really bode too well for any kind of forged 2.5 build.

MOTORS S GT

iTrader: (2)

No, we have not done any, but the blocks are std, no pinning or inserts, so why do you think Cosworth are any better ?
They cannot get around the very weak bore thickness of the OE blocks, even with pinning / inserts its still there.

APIDavid

iTrader: (4)

We see quite a few cracked Cosworth forged pistons when we rebuild previously forged engines. They fracture between the oil ring land and the piston pin land.

Look very closely when cleaning used ones before re-fitting, as they are not bomb proof.

David APi

APIDavid

iTrader: (4)

Hear, hear. I've been saying that for ages - no one listens...........

Hammer man

iTrader: (25)

What did you say? Sorry I wasn't listening

thenewgalaxy

I love listening, unfortunately I listen to too many people and then I find it difficult to make my mind up on what's right and what's wrong.

I'm not trying to wind anyone up here so please don't take it this way.

If there are inherent issues with the block I'd have expected Cosworth to reinforce theirs or machine their own thicker walled variant. But as far as I'm aware they don't, and use this much maligned engine as a base for all sorts of parts.

But I am aware there are members on here from highly respected tuners running some very impressive forged 2.5 builds.

If it is difficult to get round inherent problems with the block why are forged 2.5s still built? Surely the best option if one of these things goes is to source an entirely new engine from elsewhere that doesn't have these issues?

chopperman

What year is the CS400 ? I had it under good authority that the 2010 2.5 blocks had much thicker liners than the previous years ?

thenewgalaxy

Chopperman good sir, the car is based on the 2008MY chassis but the short block is supplied by Cosworth, it wouldn't matter which model year it was based on as that part is not used.

I guess that does not stop it being any old 2.5 block, Subaru have been making them for time.

Cosworth say in their lingo that it is honed and checked etc...

http://cosworth.com/products/perform...ck-assemblies/

But from what I gather above it would make little difference on liners as the block itself cannot take it.

As I have suggested above, surely a beefier block (or one made from tougher shït) is the answer?

chopperman

Darton liners and CDB inserts should have been on Cosworths list of modifications at the price being charged for the car imho.

rob84

iTrader: (5)

I stand to be corrected but tbh liners aren't a good solution until they settle. they can (drop/settle) causing issues with gasket sealing, which would require the engine stripping and the block decked again, which on any car would give reasons to be pissed off when it happens

chopperman

Maybe the reason from what i have read why engine builders shy away from re-lining blocks.

Don Clark

The cylinder blocks used for all 255 and 257 applications are the same (N/A applications have a different block/s).

However at some stage there has been a change in part number from 11008AA950 to 11008AA930

What the change is and when it came into production I don't know.

MOTORS S GT

iTrader: (2)

All the 2.5 scd blocks are the same liner thickness, some have more alloy in areas supporting them, but that seems to be a batch issue, I have had a few x rayed for my own personal reasons, but they are all very much the same, I have a new one here now & I can confirm there's nothing special in the bore thickness on that.
As for CS400 engines, a few have been back for rework, thats all I know, as Northampton is a very small world in the machining industry, & all CS400 block work was out sourced.

APIDavid

iTrader: (4)

They're not the same.. EJ255 is an open deck block and the EJ257 is a semi closed.

I have no idea what the part numbers represent - but for certain WRX bloxcks are not the same as STI.

David APi

Concur with Paul; SCD blocks are all the same. The only thick wall one is the W version of the 2.0 STi engine from Japan Seems it is fitted to all Hatches over there since day one. BUT it is only applicable to the 2.0.

Cosworth can check the SCD version 'til they are blue in the face; it is still not up to hard use and high power for any length of time.

thenewgalaxy

Well I feel like I've learned a lot here... basically don't bother with a 2.5 at all if you want more than 350bhp.

If you want anymore than that go for a JDM block and if you want anything relatively high power go for a stroker kit up to 2.33.

Or am I being pessimistic? I thought a forged and well-cooled road-orientated 2.5 was relatively safe for high 400s and 500ftlbs running 1.3 to 1.4 bar. Or would anything over 400bhp seriously risk blowing the block if you tried to run anything over 1bar of boost?

Don Clark

David,

Checking Subaru's database as far back as the introduction of the "G11" 2.5L all turbo versions (255/257) plus B13 255 abd S11 255 applications, have the same block part number.

Maybe the superceded part number refers now to SCD for all applications.

As also said "other" 2.5L applications have a variety of different part numbers.

joz8968

iTrader: (13)

You're correct as far as an OEM motor is concerned (assuming it's not already knackered). Apparently, too much boost is the killer, so as you say, c.350 @ <=1.3barg, is considered pretty much the max most knowledgeable/responsible specialists will push things.

As regards a properly rebuilt/forged 2.5, then that can be pushed to around 450 @, IIRC, 1.6/7barg.
Its inherent 'disproportionate' torque/response obviously makes for an effortless and satisfying roadcar.


I think this is correct, APIDavid?
If not, apologies for any (unintentional) false info.

salsa-king

my brain is frying now.

back to basics.. who's had a SUBARU warranty rebuild (with the bits they are told to replace/fit by IM etc) and then had the engine go again.. and how many miles in?

joz8968

iTrader: (13)

Yeah salsa, to make my second paragraph clear, that's a scenario if the owner simply decides to get the job done 'properly' at a specialist like API i.e. by cutting their losses and totally bypassing Subaru/IM.

In that respect, I apologise if I completely misread galaxy's question. Therefore sorry for any confusion.

salsa-king

but who's had an engine fail TWICE, after it's been fixed by SUBARU/IM under warranty?

thenewgalaxy

There are a couple on the first page of this thread.

I don't think you can learn much from a double failure, even if you're trying to demonstrate an issue.

An engine may fail again for a different reason, suggestive of general issues or bad luck.

It may fail again because only part of the engine was replaced before, for example the cylinder heads may go after a piston and head gasket repair.

But a whole new engine could mean that the car is fitted with a dodgy ECU or the engines themselves are crap. Or installed properly. Or abused or any combination thereof.

For that reason I think it's best to look at the wider issue of numbers rather than individual cases. This thread, with added input from the experts demonstrates quite a pattern if you ask me!

MOTORS S GT

iTrader: (2)

I have had a 2008 STI Hatch from a customer that had had 3 rebuilds under warranty, it had a new short motor initially, then a couple of pistons replaced, followed by another short motor caused mainly by bad workmanship from the dealer that replaced the pistons.
I know of a few that failed twice mainly due to the latter by dealers.