Bigpower

Well, after 5 years in 3 Imprezas and loads of trackdays I've suffered the big-end death rattle. Had to happen at some point I guess, but I'd like to try understand more precisely what caused it...

Background: STi6 RA Lim with Cosworth baffle plate, breathers going to RCM can returning to sump, no oil cooler yet. Road tyres (Marangoni Zeta Linea). Standard 2.0 block, Zerosports hybrid VF28, Samco inlet tract, hybrid FMIC, ported headers, 550s, Apexi PFC, around 340bhp at 1.5bar.

Suffered a big end failure after 7-8 sessions at Mallory on Saturday, engine still runs (idles fine) but has the characteristic rattle as revs die away. Exact cause not clear to me at moment, maybe someone here can advise. This may read like a catalog of errors, but bear with me.

In reverse cronological order:

1. made aware of bad mehanical noise by the detalarm, all LEDs lit at slightest boost, but no significant knock count on the PFC hand commander; retired to investigate problem.

2. couple of laps earlier, filled up with half-tank of 97RON on top of existing half-tank of 99RON plus booster. Although car is mapped for 99, we were monitoring carefully for det and didn't want to risk fuel surge. Don't think there's any evidence of det on that fuel.

3. one session earlier, stayed out a bit longer than earlier whilst reeling in a 911 GT3, and reached 130deg oil temp. Whoops. Earlier sessions were less than 10mins, reaching 110deg. Millers CFS 10w60 which has done one previous trackday and 4k road miles. Datalogit trace shows 2 bouts of 'knock' count of 15-22 at 7k rpm, whereas engine normally runs a count of around 10.

4. couple of sessions earlier, reduced boost to 1.3-1.4bar on AVCR after seeing knock count around 20 on hand commander after a session, although detalarm remained quiet (green). Started logging to see what was happening during session.

5. error of judgement led to a spin exiting Gerrards. One wheel onto grass at top of 4th gear (RA gearing, 110mph?) and 720deg spin narrowly missing barrier. Foot on clutch and engine still running. Back to pits to check and calm down.

6. first time at Mallory and realised it's v.quick except for the hairpin. Fuel consumption through the roof. Gerrards long right-hander (like Coram or Chris curve but faster) could see oil pressure drop from 6.0 to 5.5 bar on some laps. Had fuel surge once (I think) at Devil's elbow, a 4th gear lefthander that drops away.

7. before the trackday had various short bouts of det due firstly to dodgy crank position sensor (now replaced) and to compressor surge (Paul at Zen's assessment, from the logs). Boost reduced in midrange to avoid the surge.

8. Oulton trackday a few months ago, before compressor surge problem was realised, with brief bouts of knock count 30-40. All apparently ok subsequently, but perhaps the seeds of damage were sown back then?

Apologies for going on a bit. Anyone care to comment on relative importance of the possible causes?

Andy

Sorry to hear the news Andy. When my engine was rebuilt (the STI you bought from me), the mechanic said it was down to the oil pump efficiency deteriorating over the years. Did your RA have a modified pump or the original unit?

I was going to say the same. Don't think it's a det issue but more the oil pump failing or oil related.

Same thing happened on my WRX. RCM modified oil pump should go some way to making sure that doesn't happen again.

Duncan had a problem with his Cosworth Baffle plate, it cracked the sump oil pick up pipe and he was subsequently sucking in air instead of oil. He didn't rate it very highly either if i remember rightly. Get the sump off and see what's what.

Sorry to hear this Andy.

I think John Felstead hit the nail on the head on 22b.com ... Properly baffled sump next time, some shorter oil change intervals, oil cooler to keep it in pristine condition, better fuel and it should last.

Nothing wrong with the cosworth baffle plate at all (more a case of the pick up pipe could have been broken when originally fitted when the engine was built) New pick up pipe and no issue. I still use mine and rate it higher at controlling breathing but it isnt a substitute for proper baffles.

Oil pump - don't think so at all.

You'll know whether the failure is knock related once the heads are off. You could have a faulty OE knock sensor, although unlikely.

I used to see high knock counts with the Apexi (only because it gave a reading). Starting would see mid-teens. 70 wasn't unusual although I tried not to let it get there.

Oil and fuel surge happen on long fast right handers, not lefts. The spin, if anti-clockwise could have been the problem with oil surge. Unfortunately, Guages only record peak highs not lows and unless you have a record and playback, like Defi's and are actually recording at the time, you'll never know.

I've run the oil to 130oC without a problem but tried to keep the ceiling to 125o. Difficult when the car you've been chasing is within reach. I'd have changed the oil for a track day if it'd done 4K miles and a track day already, especially with no cooler.

Silly move IMO putting 97RON on a 99RON map. Hope it wasn't BP Ultimate? That would have had the Detalarm and the Apexi lighting up.

Don't worry, Logan will be along to tell you how crap Imprezas are and to buy his Evo.

Sorry to hear it's gone Andy. Just hope the crank's survived.

duncan wrote:
Nothing wrong with the cosworth baffle plate at all (more a case of the pick up pipe could have been broken when originally fitted when the engine was built) New pick up pipe and no issue. I still use mine and rate it higher at controlling breathing but it isnt a substitute for proper baffles.
.

Sorry my mistake, i thought you had some issues with the baffle plate and were trying to sell it at one stage but clearly you've sorted it out.

I must keep up

Thanks all, much appreciated.

Age of the oil - yup, that was remiss, I hold my hands up to that. Previously I've kept to 3k miles including 2 trackdays as a maximum.

Temperature of oil - reaching 130deg on one session was remiss too. Will check accuracy of sender in due course to make sure it's not under (or over) reading.

Oil pressure - was holding 6bar rock steady, as it always has on the road, except for the 0.5bar drop round Gerrards (co-driver watched the gauge all the way round Gerrards on several occasions). However, not sure of pressure on the one session when it got hot (was distracted chasing the GT3).

Baffled sump - have one on the way, but sadly not fitted yet. Will retain the Cosworth plate as well, on Paul at Zen's advice.

Drove Ian (DaOne)'s 2.1 stroker with 20g last night, very impressed ... only issue is that EngineTuner is in Plymouth! Looking at the various options now...

Andy

If a normally rock steady oil pressure suddenly drops 0.5 bar. Something's out of the ordinary and should be immediately investigated or at least back off.

Too late now though.

Was a bit variable rather than a consistent sudden drop. One lap it held 6.0 then dipped 0.5bar briefly near the exit. One lap it sagged by up to 0.5bar for few secs before recovering. Some laps it was ok. This was from the passenger watching the gauge on a selection of laps; datalogging would be better. Backing off would have been even better...

Gerry H wrote:Don't worry, Logan will be along to tell you how crap Imprezas are and to buy his Evo.

Sorry to hear it's gone Andy. Just hope the crank's survived.

Thanks Gerry, saved me typing

I doubt the crank will be okay, the 2nd time mine went it was only a very light rattle and only when the car was warm, and the crank was scored enough to replace it.

Andy, sorry to hear its gone. What I would do is have a serious think as to what you want in a car.

As I know its a easy option to go down the forged engine route with all the bits, but as you are probably aware this is not cheap, and you need to spend a lot of cash on all the other bits to make the oil system bullet proof etc. Its a very slippery slope!

If you aren't that fussed in doing that, then look at chucking a 2nd hand engine in it, taking all the nice bits off it a flogging it, and buy something else. In hindsight that's what I should of done when mine went.