Bob Rawle

Actually its usually cylinder overheating due to lean running from a tired maf OR inferior (I will use that phrase) oil and sometimes servicing procedure that normally causes big ends to go. If a cylinder overheats it will nip the piston which will do the big end, poor oil quality will mean oil film breakdown and pickup when the car is driven aggressively. Det can cause it of course by again raising temps and increasing shock loads but det us usually caused by lean running or poor fuel, again lean running is going to cause nip. Poor fuel will allow det to take place again leading to raised temps leading to ...

So this is not "always caused by det", that's a fallacy.

However the P1 engine IS an Sti5 engine lock stock and two smoking ... so treat accordingly.

bob

Bob Rawle

"after stripping down engines that have failed due to crank / bearing failure the pistons look A1, no signs of det at all!"

Hmm as I indicated mostly due to piston nip from overheating.

bob

Matt Beau

Detonation, or more specifically pre-ignition, can cause big spikes in cylinder pressure. Imagine the piston going up and down, and then having a sudden hammering being appiled to the top of the piston. This force gets transferred down the rod on to the top-bearing shell. This load then squeezes the thin film of oil and loads the bearing abnormally. If the upper bearing shells fall out of the conrods, it's an almost definite sign the engine has been detted badly.

Little to no piston damage may result from this infrequent detting that accumulates damage to the bearings over time. High peak cylinder pressures can also result from aggressive ignition timing even if detting isn't occuring though. Just takes longer to fail.

Your ring side clearance will also be an indicator of how much detting was going on.

dowser

Hhmmm - intersting discussion. My engine has suffered (far) more det than most, but is still in one piece. I am very careful/nervous about TB intake temps, and EGBP, plus the related effects.

All of the failed MAF cars I've seen (CH's biggest MAF customer ) have actually performed better than standard once turbo has spooled (stutters during spool generally), only one had (what I would call) really bad det at the time and it also had fuelling issues. Normally they're just a little 'sparkly', which isn't necessarily a bad thing (IMHO and on my own engine ).

The only big end failure I've inspected photos from was not (according to piston surfaces) suffering from det, but failed on a rolling road run. Water temps were around 110 degrees mid-WOT just beforehand.

I go with the piston nip theory from a logical perspective.

Richard

Bob Rawle

Its clear det will cause bearing film breakdown if its severe and prolonged but its more likely to melt the piston crown first imho but to state that det is the main cause is misleading and erroneous as its only one of the things that could contribute and then most times doesn't. These engines as std have miniscule piston to bore clearance.
However a sever det event will cause an "inferior" oil film to break down causing local pickup, the bearing may not fail straight away however at some point when the engine is being stressed it will fail with the results we are aware of.

Like Richard my cars "have" to suffer some det from time to time in the interests of R & D however my bearings are still very much intact.

bob

krazy

How does the ecu measure load values?
ie. does the speed de-limiter show a slower than actual speed to the ecu, which then assumes a lower load value and hence make the high load/rpm leaner than ideal?

Bob Rawle

The engine load value is not affected by the speed of the car.

It factors together rpm, tps, maf output and map output to come up with load.

bob

dowser

Sorry, but you wouldn't necessarily notice det. Consider what your engine is doing at peak torque and ~1.2 bar or more of boost. I'm sure everyone will differ, but if an engine is in a dangerous state I class it as 'feathery' - this means (for me) that it's not happy during transitions.

I think that what Bob is suggesting is that a failing MAF can increase in-cylinder temps enough to cause a failure before any (visible) det related damage to piston crowns occurs. An uncontrolled explosion can leave pistons unmarked, but whack the hell out of the bearings.....

I (personally) believed (previously) that a Subaru engine is very strong if it doesn't see det; I'm starting to modify this so that it's strong if it doesn't see high in-cylinder temps. The 2 are not necessarily (but can be) related.......

Richard

p1stew

All very interesting chaps, but for the non-technical among us what is the best method ( if any ) of stopping this occuring again ?

After speaking with the dealer my engine has thrown con-rod no.4 and is need of a crank. My dealer has however claimed for everything possible inc. pistons , oil pump etc.

i have been informed that IM will provide the parts but i will have to stump up for the labour costs. ( warranty ended six months ago but car has more main dealer service history than req'd and only done 40k) Is this fair or should i persue the matter further ?

as you can appreciate just want to minimalise risk of it happening again. Your help is appreciated and it's nice to know that their are actually people out there that know wot there talking about !!

krazy

What sort of labour costs are they quoting?
Don't know how you'd fare persuing further if the warranty ended 6 mths ago..
Did they find a reason for the failure?

p1stew

around £1500 approx 2 days work. I've heard no response from the garage themselves, however they were quite interested that another garage i had spoke to ( in keyworth ) had ideas of why it might have happened and said it was a know problem

nom

Preventative measures...

Good oil (Motul 300v or similar - which means not very many oils at all!) with regular & good servicing following the correct procedures (this will whack out many of the Subaru garages, note...), ensure that the MAF is in good working order - ultimately keep an eye on AFR (which would also mean the MAF state can be seen relatively easily), ensure only good fuel is used with a KnockLink to keep an eye on this - especially after a fill-up - with some booster in the boot for if it is a dodgy batch. Measuring EGTs would also be good...
A more 'active' role could be taken by installing a water-injection system to control det & cool the in-cylinder temps, and a 'J&S Safeguard' type gadget (additional det control thingy) if you engine seems to be det-happy - which some are - or aren't 100% convinced by the ECU's det control (can become a problem in some cases with some aftermarket headers).

Phew

p1stew

allways had mobil 1, oil changed over and above service intervals.

Would it be wise to have an ecutek engine management fitted and a remap?

p1stew

moreover \

i had the car on the subaru diagnostic equipment times many and it never picked up any faults

nom

The diagnostic kit doesn't pick up some of the critical faults (e.g. failing MAF sensor) - you need to go to a Subaru specialist rather than a dealer for that
The grade of Mobil 1 can make quite a difference, and the correct filling procedure needs to be followed (unfortunately it's marginally more complicated than swap filter/bung oil in).
A remap is a good safety move IMHO on the P1, yes, unless you have a ready supply of 102RON fuel in your back yard somewhere...

Another thing - holding the car for any length of time above ~110mph will cause it to overheat, oil to break down, etc. etc., especially so on the JDM market ones (so effectively the P1) as the aerodynamics/ECU/engine were never intended to go over this, so are not set up for it. I wouldn't do it even one which is set up for it without a close eye on oil & EGT temps. I haven't done 'extensive testing' as I'm not in the right part of the world for that, but someone noticed that after 5 or 6 minutes at ~140mph, the level of engine noise (as shown by the KnockLink) begins to rise, then the oil temp; shortly, the KL begins to get quite animated. He chickened out then (sensibly!) but doubtless carrying on like that would have created some serious wear on the engine, if not actually causing serious damage...

Bob Rawle

My comments are to indicate that det COULD" contribute, high speed runs as described induce very high cylinder temps as the car is running cruise fueling and egt's etc get high, but oil film integrity makes the difference. So then we get posible nip/oil degradation or a combination. There is no way to pin this to a single element, its a combination of circumstances that lead to failure.

Its also an incorrect generality to say that oil pumps etc are the main cause, untrue, sticky pressure relief plungers are a known problem but under high engine revs, if it stuck, you would still get good oil pressure, it would only drop off at lower revs.

Bob

p1stew

i'm sure it's 15 50w. I was at ther time doing at 70 on the motorway ( makes a change ) when i heard a slight noise from the engine which decreased when i lifted off, Whilst the engine was still working when i'd pulled up , hence not massive amountof damage, not sure how much longer iut would have lasted before the big bang.

so what we are saying is

1. a good idea to upgrade the engine management system and get it re-mapped
2. use optimax if available
3. check for failing ( MAF sensor ) how ?
4. use fully synthetic 15:50 oil
5. Upgrade oil pump?

Any other things for track use or extended high speed driving?

RALLYSLAG

just purchased 96 uk spec bru / dealer told me to use 10/40 semi
which i did ,on saturday decided to take part in local tack day
what a big mistake / yes u got it bottom end whent guess ive over reved it
but not yet stripped it (project saturday)

Dark Blue Mark

I can get detailed oil analysis if need be

MB

Dark Blue Mark

Widey, *SOME* JDM cars rev higher, but its only 1k rpm, and that's on STi's.

Its not much use either due to the power curve of the car. Ive never been near the redline in higher hears on mine...

MB

Simon Lines

It's not so much the size of the scoop as the imbalance in size between the scoop and the front entries. As the speed comes up the front (big) entries start to pressurise the bay, this essentially stalls the intercooler!

High speed running (over 110) results in the various coolers getting less and less airflow (front rads and intercooler) I have spent some time flat out at circa 169.8 (sat nav verified) and I watched all the temps (I had an inlet temp K type fitted) climbing and climbing until I had to abort the run.

Just for info, we are talking just a few min's...

I was forcibly reminded of this event recently as I am running into these issues on my own vehicle at present ( www.tunertek.com/sigc8 )

Opening the hood vents seems to help but I have no hard data yet

Cheers

Simon

krazy

Umm if u can manage 169.8 mph, am I right in assuming your car is modified a fair bit?
Thus the cooling systems may not be up 2 the job anyway?
Although it is a likely possibility, since the classic design was sold in countries outside japan without the 110mph limiter, surely they would of tested the aerodynamics/airflow at higher speeds?

TonyBurns

iTrader: (3)

Simon,
Isnt the theory about lack of free air flow over the intercooler at higher speeds one of the reasons Subaru changed the shape of the blob eyed STi's intercooler and added the splitter so it would get better airflow at higher speeds??

Cheers!
Tony

Simon Lines

169.8 was with a std car

Cheers

Simon

dowser

Thanks Simon,

Any quick and/or dirty fixes you can recommend? I've seen the effect increase after fitting a 6MT gearbox, which I guess suggests there's less flow through the engine bay. I initially assumed the TB temp increase was a result of not as much air being able to get through the intercooler, but after the above snippet it could also be air through the front openings blocking flow through the i/c scoop?

Only things I can think of will create front end lift......but I don't know how much or how dangerous it would be.

Richard

Simon Lines

To be honest I believe that if you want to run consistent high speed reliably the only way to go on a classic is FMIC or Air to Water, I would be happy to be proved wrong but everything I have seen so far suggests this is the case. I too have noticed the decrease in flow since the 6MT went in the tunnel, I use a simple manometer for testing heat exchanger flow, basic but it works, I also use wool tufts for body work and duct entry / exit

Cheers

Simon

nom

i.e. I think you're buggered, Richard
Unless you want to swap countries, that is?

dowser

Thanks Simon. I don't need consistent high speed, but I do need enough airflow for a 30 minute track session without too much 'heat creep'. It used to stabilse at an acceptable point on the 5MT, but it's a little too high with 6MT (although bigger scoop helped). I'm currently running sub-optimal timing to cater for the track environment.

Am going through the process of better under bonnet heat management, plus putting the airbox back in. We'll see

Richard

Bob Rawle

Which is why the first mod for serious work is to take off the undertray if fitted, GC* Type R's etc have undertrays fitted, I always recommend removal. The larger MY03 scoop and splitter will allow a higher pressure to be built up on top of the intercooler which will narurally help overcome any engine bay influence, removing the bonnet vents might help.

I actualy did a flow check on my STi5, measured the air flow into the scoop, on that car it always increased with speed, but the car has no under tray and a FMIC which would reduce the pressure build up in the bay.

bob

dowser

My undertray is also long gone. I'm considering trying to run a couple of lengths of 4" flexible hosing from engine bay to a low pressure area to assist, but the main issue iseems to be space! Secondary (but should maybe primary!) issue is generating pressure in area's previously not used to it.

I should also add that I still haven't added i/c water spray, or WI. Both would also assist, but I want to get things as optimal as poss passively before deploying them.

Richard