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DBredS4

Blown Turbos

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I was wondering about the spate of blown turbo and while reading Practical Performance Car I had a little epiphany of sorts.

I then posted this on PPC's own forum:

'Hello all, haven't posted much on this forum but as I'm a avid reader I thought I'd open this to a wider audience.

Well, had a little epiphany of sorts. I was reading the Dave Walkers Tuning (my favourite) section this morning and it occurred to me that the reason so many turbos are blowing on our cars (4cyl Esprits) might just have found a solution.

He mentions an R36 running higher than 'normal' boost with a Rotrax supercharger and the risks of pre ignition due to the spark plug running temps, ie the more power you run then you need a plug that runs cooler too.

Got me thinking as we have a spate of blown turbos on 'chipped' and souped up 4 cylinders which we have been putting down to flexing of the turbo shaft clipping the edge of the housing hence losing a blade, smoke, loss of power, trip to specialist with a big bill. All to my knowledge run stock plugs. NGK EPR6EKN or something.

I wondered if the problem was actually a spark plug losing its tip which when sent through the exhaust valves and down the pipes was actually causing the turbo to blow. Running on 3 cylinders would be not really noticeable because we simply pull over and get a low loader ride to the shop.

Any suggestions, comments, laughter, piss taking welcome...

I wonder whether I was just grasping at straws or investing in a cooler running Denso Iridium plug might be wise...

Cheers

Dom

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Upgrade today to remove Google ads and support TLF.

When this happened to mine, all I did was to bolt on a PUK supplied shiny new one.

turbo003-1.jpg

If the failure had been attributed to a piece of spark plug then I'd be expecting the car to run on three cylinders upon re-start. Interesting theory and probably the cause of some issues, but I think it'd become apparent during the repair.

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Ive been scratching my head on this one and had to delve into my old physics books.

But from what Ive found

- to get more boost into the engine you need to get more air into it

- to get more air into it, your compressor either needs to be modified to give more airflow for a give compressor speed or spin faster

- compressing air causes heating, some of which will be experience by the compressor

Let assume that we are allowing the turbo to spin faster to achieve it.

A spinning object experiences a force which, according to the physics text book can be calculated as;

(((Revolutions of the object squared x radius of the circle) x mass of object ) / Pi squared) = force

So lets assume some very simple numbers.

If we say 100,000 rpm, compressor radius of 2.5cm and turbine mass of 150 grams, we have a raw force of 379.9KN.

Lets get more boost by increasing the rpm to 110,000 and the raw force is up to 459.7KN.

So in summary - by achieving increased boosts, are we potentially exposing the materials of the turbine to forces beyond the material structural limit?

Now my head hurts, over to those who know better for their thoughts and possibly need to correct my useage of units of measure.

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(wrong section btw)

From what I have been reading and looking into the selection of the turbo vs increasing the boost past normal setting is a bit of a riskay area.

Increasing the boost (compresser rpm) will cuase more mechanical force on the unit - turbos are hard as nails IF they are worked in their specified parameters and maintained.

Increased boost also causes additional heat but without taking readings from the compressor itself it's hard to know what the resulting temp is.

Finally - and this is only my opinion - there is a question of the Esprit's overboost feature. As far as I know chips will make the turbo spool earlier in the rev range and the only way they can do this is to allow the wastegate solenoid to operate lower in the rpm scale (5000 down to 3000 rpm kick in) - this creates a massive and rapid speed increase as the turbo basically goes into open loop and the pressure is un-regulated by wastegate solenoids at 90-100% duty cycle...

...IMO that operation can cause damage, you cant rev an engiine that quickly and the same applies for all rotating machines. That turbo is only meant to really operate at 0.65bar - the ECU opens it to 0.85bar by moderating the wastegate solenoid to build more boost (rpm).

If you just let the thing accelerate from 0-100,000 rpm in a split second it's obvious that it will increase it's chance of failure becuase it is operating outside of normal parameters.

The thing really boils down to the more performance the more maintenance you have to spend, if that is acceptable offset for the increased power then fine but if people complain about reliability probs after they've frigged with the ECU and boost paterns then you could say you had it coming !

More I read into chips and the like the more I dont think they are necessarily a good long term idea for a stock turbo, apart from improving the base code (ie SE -> S4s). Of course I must add I haven't had the opportunity to test chips out and by that I mean not driving the car but by looking at the hard code- driving a car that bring max boost in much earlier that normal will of course feel like a rocket.

Edited by Jonathan

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The turbos do have limits, but they aren't set at .65bar and xxxrpm per se.

The turbos are more efficient over a given range of conditions for a give pressure ratio and engine size and yadda yadda.

If you go outside of that range, then the turbo will not be operating within its most efficient zone. If you go too far out of the range, say past the "surge line" then the turbo will be stressed to a point where it may fail.

I suggest reading

http://www.turbobygarrett.com/turbobygarre...ech_center.html

with that information it is possible to calculate the range where a certain turbo is most efficient and see if your planned mods will allow the turbo to be in a good range


Travis

Vulcan Grey 89SE

My Lotus Photo and Projects Album

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Also, a chipped SP tip would result in serious damage to the piston and head. This happened to me in 94ish to an Escort RS. They put the wrong plugs in and a piece of the ceramic isolator was set free in the chamber. This thing broke a piece of the valve, mae the head and the piston look like it was sandblasted with hammer heads.....

So if a plug goes, the chamber should be seriously injured.

To diagnose right , get one of those USB PC endoscopes ( 80 Euro or so....) to check the inside of each chamber.


Olaf S400 project www.esprits4.de

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Definately not Spark plugs....having had 4 failures in 5 years of ownership the cause is warped turbine blades due to the over excessive heat build up running at over specced boost. Spark plugs have always been intact.

To be honest my last Turbo (current and logest lasting) has only lasted this long due to the fact I know now with experience when to let off the gas.

She'll pull like a train but on continuous boost of say 7 secs+ let off or she'll definately go pop like the others did.

ITs been an expensive lesson

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Waynef,

Have you ever done the calcs to see where you fall in the compressor map for your turbo?

Are you past the surge line with too big/heavy of a turbo, and damaging the blades with shocks from throttle changes? Or are you past the choke line with too small of a turbo and overspeeding it?

My friend has a highly modified Esprit X180-R (T3-4 hybrid, blue race, more fuel...) and his turbine housing cracked in many places from excessive heat due to an exhaust manifold coating, but the turbine blades were fine.


Travis

Vulcan Grey 89SE

My Lotus Photo and Projects Album

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If your running an uprated turbo that is supplied as being fit for the chip fitted then surely replacing it every year due to the shaft flexing & turbines getting mashed against the housing is crap and the supplier is selling a pile of shit thats not suitable for the job its been spec'd for?

Only being able to run full throttle for 7 seconds and then having to lift off must be massively frustrating, the supplier should be revising the specification of their turbo internals and refunding everyone all of the money they've had to blow (quite literally) on replacement turbos!

If I was being charged


Chunky Lover

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I think the questions been answered in your post Simon....chip number 5 is not a standard on the S4 so running the engine at well over its maximum recommended boost with the extra high exhaust gas temperatures and manifold temps is only going to make the turbo fail quicker.

7 secs of continuous acceleration is ample and will propel you well into 3 figure speeds.

The Turbo its self boosts as normal from 3000 revs and pulls through to the redline however as it passes 7000rpm it hits what can only be described as another powerband and free revs the turbo flicking the needle to inexcess of 8000rpm. I believe chip 5 does up the redline to 8200 (maybe someone can clarify this). However this is the point if she is going to go she will.

I believe the issue is at the over boost state the exhaust turbine is causing huge pressure differential between the intake turbine causing extra heat build up and metal fatigue. Proof of the pudding is same Turbo now for approx one year. If i wanted to blow it all i'd have to do is ignore the over boost at high revs keep the gas on and she will definately go.

The fact is that factory settings would never put the turbo into these conditions in the first place. I guess upping the power will have consequences, but i'm happy with my cars performance and i guess thats all that matters.

Waynef

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I think we've found the cause of your turbo problems Wayne! 8,200 rpm is pretty insane for a stock engine :devil:


88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

Evora NA

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... Markus changed mine to, I believe, 8200 and we were advised by Garry to narrow the oilduct, going from block to head. I would have to ask Steffen what the exact diameter was, but seems to be plausible to keep more oil in the sump at higher rpm...

I have not had the pleasure of going to that range as of yet, kinda just parked the car in the garage after surgery....( my personal surgery of last year...:-( )


Olaf S400 project www.esprits4.de

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interesting stuff chaps, especially the mention of the blades scoring the turbine housing, Jeff has got the turbos now with 'clipped' blades to give a very slight gap to the inside of the housing to help prevent them 'pinging' off. Mine is modified thus as is at least one other unit.

The downside is a tad more lag but if it means reliability well fine. As it is, if you keep it on boost, the power is there so I am not fretting. I cannot afford more turbos going pop, just had a new steering rack and a few other jobs done which is renewing the life of the car for another 100k or so.

Dom

ps I was under the impression that Marcus upped the rev limit by only about 100-150rpm? Correct me if I'm wrong...

Edited by DBredS4

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