Gear Head

iTrader: (2)

Having just bought myself an sti 3 with the no.3 (firing order) big end gone, I am curious as to its cause.
Having to spoke to David at API and then Roger Clark Motorsport, I am even more confused.
David said that the main cause is increasing inlet temps when cruising at 80mph+. He said that the scoop effectively stops working at these speeds. But he then said that a remap can fix the problem? Surely a front mount would be more appropriate than just a remap? And I would have thought that this effect would cause detonation, killing the piston, not a knackered big end. And why only no.3?

Not sure who I spoke to at RGM, but they said that this isn't the case at all, and that 9 times out of ten it is the relief valve failing in the oil pump, or poor quality oil.

RGM's theory makes more sence. If Davids theory is correct, why is it always no.3 that fails?
Atleast with the oil pump failure, no.3 is the furthest away from the source.
Not knocking you at all David, but there are so many myths when it comes to EJ20 failures!

adrianp

It's probably a bit of both...

Could well have something to do with heat though as No3 has the turbo sitting next to it...

stockcar

oil pump failure is an old one that most tuners would tend to steer away from now...............most people now agree that the relief valve sticks on most occacssions because of the debris from the b/end failure rather than causing it..................

the reason that the b/ends generally go is because of detonation overloading / overheating the crank and causing a breakdown of the oil film..........

just as an aside when the pistons fail (usually cracking the ring land) its generally no.4 in our experience, just to add another 'myth' to the list.......

alyn

RRE

Could you clarify one thing for me. You states that the TMIC will not work over 80 mph. Is that because of the scoop? I mean, if it does not work over 80 mph there would be ALOT of engine damages? Or am I missing the point?

Gear Head

iTrader: (2)

Thats not what I said, thats what API David said.

The Rig

iTrader: (13)

Fitt the bigger scoop,STI8 etc.

isnt that why they (STI8 ETC)have the big scoop anyway ?

MrRA

I believe No.3 cylinder is closest to the turbo. It is also last to receive it's fuel to the poor OE fuel setup. Being closest to the turbo means that it in theory it will be running slightly hotter than the rest. Because it also receives it's fuel last any fuel pressure anomalies will be felt most here.

I also agree with RCM's statement of the oil pressure relief valve. I believe that's why they supply their own modified oil pump.

I'm not too sure about the Scoop not working above 80mph. I mean look at the in car vid of the Spec C doing a lap of the 'Ring. It is constantly flat out for the best part of 8mins so I would've thought that if the I/C were receiving no cool air then it wouldn't have survived the lap at all.

The I/C scoop is designed in such a way so that it achieves a 'ram air' function to force air down over over the I/C.

New_scooby_04

iTrader: (4)

Chris,

David is right about the std TMIC and Scoop being ineffective at high cruising speeds on the pre hawkeye models, due to poor aerodynamics: apparently the problem is that above a certain speed the air just goes over the top of the scoop! Even Subaru acknowledged this by first putting a Scoop the size of a post box on the Blobeye STis and then changing the front end completely on the Hawkeye, hence reverting back to a smaller scoop.

That said, one shouldn't be too paranoid!! The car isn't going to blow up as soon as you stray over 80mph. My car was mapped in 30 degree plus temps with the std MY99 TMIC and made 319bhp without any det!

I just wouldn't hit the autobahn at a steady 120mph for an hour is all!!

Using top notch fuel and oil all helps too!

AFAIK Mr RA is spot on about the No 3 cylinder and oil pump problem!

Besides, why would you go above 70mph anyway- that's the limit you know

Ns "I'm still getting a FMIC though" 04

Pete

So basically new scooby, you`re ok going OVER 80 and above, but only if it`s for short bursts?? but if you sit at 80-90+ for longish peroids, nasty things can happen?

Right, now i know i`m going to get blagged here by the knock link haters, but shorly having one of these fitted would/should tell you if any horror stories are taking place??

Go easy on me folks, i`m still learning...lol

ZEN Performance

measurement of the inlet charge shows the TMIC works fine at 80, 90 even 100 and above MPH. But if the TMIC is physically too small, it will just get overcome with heat no matter what the road speed.

I would say about half the big end failures we see are accompanied by loose screws on the oil pump blacking plate, which will cause a loss of oil pressure at high RPM due to leakage past the plate. Other failures are can be attributed to abuse, poor servicing, poor oil, and a few failures just have no obvious causes.

New_scooby_04

iTrader: (4)

All other things being well, I think you'd have to sustain 3 figure speeds for it to be a problem mate

I've got a knocklink and have never seen any activity at high speed cruising, but then again, I don't break the speed limit *coughs*

I would have thought it would give you some warning, if I understand it correctly, as the temps get higher, that's when the DET starts to set in and from there the failure can happen very quickly.

PS There is nothing silly about having a knocklink, especially if you have a tuned car!!

PPS Just noticed you have an STi RA. I'm assuming it's been mapped for UK fuel, running a JDM on the incorrect grade of fuel would be the biggest concern in terms of engine failure!

Gear Head

iTrader: (2)

Its not an ra, its an sti 3. As far as fueling goes, the setup is standard. I was under the impression that 100ron fuel was not the norm in Japland until 2000, meaning all jap pre 2000 imprezas are NOT mapped for 100ron fuel, but 98.

New_scooby_04

iTrader: (4)

I believe that's correct (although I know less about the Classic Stis than the UK Turbos). IIRC it was the Sti 5 and 6s that were intended for 100RON.

If the above is true, put V Power in it and you'll be fine!

terryb

Chris

I would say that the stress of detonation on the piston crown would be transmitted through the conrod to the big end bearing, causing potential bearing failure - especially if the oil is old/ poor quality.

Just my thought

Terry

APIDavid

iTrader: (4)

Really frustrated here I just put a great long thought out, explanation in the thread as how we at APi see it and the damn 'system' has gone down momentarily across the midlands and lost it into the ether.

B*GGER

David APi

I might do it again tomorrow.

p1mark

David / Paul

With regards to the notion of detonation related shocks being transmitted down the rods and causing bearing failure......

Is this a proven cause? I ask because on other engines i have been involved with that have suffered detonation i have never seen this. I have stripped/built 2 Subaru engines now with big end failure that had no apparent cause - oil pump cover screws tight etc - but the failure was of the bearing contained in the cap and crank damage/scuffing was substantially worse on the underside of the pin. This does not make sense.

I understand the massively higher loads caused by det over and above normal combustion, but this obviously occurs slightly before TDC. At this point the piston is on its upstroke, hence load is most at the bearing contained in the rod, the bearing in the cap has negligable load.

Why then, on a very large percentage of big end failures that i have seen on bikes and cars, is the cap bearing the one that has suffered?

I do know for a fact that angle of oil exit from the oilway to bearing (as regards to TDC) is critical. I believe this has changed on the newer cranks? Is this not an admittance by Subaru that one of themajor causes of failure is purely an oil control issue, combined with bearing material that was not always up to the job.

Or, does detonation continue until past TDC, at which point it would make more sense for the bearing in the cap to suffer?

In the event of detonation being severe enough to knock out a bearing, would you not expect to see piston damage?

Gear Head

iTrader: (2)

Exactly! If it was 'pre-ignition' then surely you'd see piston damage??

Northern Nick

iTrader: (1)

I tend to agree with the scoop theory and the turbo location being part of the problem with number 3 big end failure. But our fuel is poor quality compared to Japanese fuel even if it is the same octane rating. Look at Tesco 99ron, its rubish compared to Shell 98ron.

Pre-ignition causes the heat which thins the oil which cause big end failure. Dispite common belief, scooby pistons are quite tuff.

My mate WRX 94MY knocked 3 No. 3 big ends out with in 12 months, in the end we swapped the engine for a legacy lump and retained the WRX heads.

Putting that aside, the next stage of modification was an aftermarket ECU because thinking along the lines of ignition and fueling causing the previous engine failures, adjustablility would help prevent it happening again.

The map man involved was the living legend (imo (No offence Steve)) Andy Forrest, he took the car for a run pre fitting the PFC ECU and said he was being defend by det before 3000rpm on the origanal ECU through the det cans. Fitting the Apexi and getting it mapped was the best thing my mate ever did to his WRX, knock levels on the commander never go past 25 and the car was faster, smoother and better on fuel.

I'd recommend anybody with an import Impreza to buy an aftermarket ECU as there first mod if your worried your going to have or have had big end trouble and get it mapped by somebody good like Andy or Steve.

Dont know if you guys agree?

Hol

iTrader: (1)

Accelerating uphill with 5 guys in your car at over 4000rpm was another one I heard off.

It this case it was a 22B and I think the extra load on the crank did the job. (Similar point to Terry's).

Has anyone ever noticed that after 4000rpm on a cruise the oil starts to get hotter quicker?

I noticed it on my Type R, with both the standard and Vlimited gear sets and also on my new age.

RedScoob

Just a quickie..... Is the small end ("wrist" of the piston, I think that's right?) that much tougher than the crank bearings?
Just seems strange that if detonation is the cause, that the componants furthest away suffer the most damage?

Northern Nick

iTrader: (1)

The enigine runs lean at cruise, hence heating the oil.

My Celica turbo was glowing orange/white on standard ecu sitting at 85mph on the motorway because of the lean running (better fuel economy).

Northern Nick

iTrader: (1)

The little end is just a pivet and moves alot less than the big end

Pete

Forgive me here folks, but i`m newish to the Subaru scene and when i read posts like this it really makes me worried. The topic in question, does this happen on a REGUALAR basis to cars?? i`ve had my car mapped @ API by pat and David and a fantastic job they`ve done too. Now again bare with me here, having had my car mapped, does this shorten my odds of big end failure etc???



........Pete.

Gear Head

iTrader: (2)

yes, you should be fine.

swtmerce

Something I don't understand here. The standard ECUs have knock correction right? So, is it just a bit useless on the early cars or are there actually more engine failures related to det on cars with aftermarket ECUs like the Apexi which doesn't have knock correction?

Northern Nick

iTrader: (1)

I'll be honest with you here, I'm not sure why the standard ecu caused all the trouble but it did. Maybe it only works to a small tolerence, I'm not sure.

Aftermarket ECU's imo only give det if something changes, a modification without getting it mapped in, bad maintanance, dirty/cheap fuel or they've been badly mapped to start with. All being car nuts, I guessing non of the above should happen.

I dont understand what you mean by "are there actually more engine failures related to det on cars with aftermarket ECU's"?

Apexi doesn't have knock retard but any mapper worth his salt will map a car to a SAFE limit, allowing for the most likely things that could go wrong to be tolerated for a short while until you notice/get it fixed.