Map + Boost Leak = Dead Turbo?

[Rolls]

I have a question. Lets say you have a turbo with an ecu that runs a MAP sensor opposed to the stock AFM and a boost leak. What I propose will happen is the air will leak out of the pipes causing the boost to never reach the set level (say 10psi) because of this the turbo keeps spinning harder and harder trying to reach the 10psi however due to the leak it cannot. As the ECU is reading the correct pressure (and temp) in the pipes it injects the correct amount of fuel allowing the car to drive properly. Now would the turbo just keep spinning harder and harder or at least as hard as it has to to reach the boost pressure with the leak, this would cause far more wear and may even destroy it instantly if the leak is bad enough? If so how would you protect against this?

I know with an AFM car the AFM will read more air than is really going into the engine, so the engine massively overfuels causing it to barely run, you then go 'oh shit I have a boost leak' and fix it immediately.

Anyway I am curious as to if my thinking is correct and what you people think about this. As if correct, this could be the source for a lot of turbo failures or accelerated wear on MAP tuned cars.

I guess ultimately it comes down to how much harder the turbo has to spin to overcome the boost leak, if it is 10% it probably doesn't matter, if it is 100% then it would. However if the boost leak has to be so large to make it spin 100% harder, then there probably wouldn't be enough exhaust gas to spin it this hard. I imagine the problem would be more pronounced with smaller (stock) turbos.

Edited February 4, 2010 by Rolls

[paulr33]

with a leak i dont think pressure would exceed a high enough level to damage it

with a reasonable leak i dont think boost would go much past a couple of psi, if that

so the turbocharger would be spinning fast enough to damage it

however

if you clamp the voltage of the map sensor, or it fails and gives a bogus reading

then depending on your boost control, you may have unlimited boost

as the actuator spring never see's pressure, as map tells the solenoid not to open, so it never does

this in turn runs unlimited boost and can kill shit

[Rolls]

with a leak i dont think pressure would exceed a high enough level to damage it

with a reasonable leak i dont think boost would go much past a couple of psi, if that

so the turbocharger would be spinning fast enough to damage it

Do you mean turbo speed/air flow? Because once the pressure reaches say the set limit (eg 10psi) it will open the gate and stop increasing. If you did mean turbo speed then yeah that is my question I guess, how much faster it will spin. Do you agree that it would spin faster though? Because any increase in speed would make this a problem big enough to look into, as any increase in speed will wear your turbo faster.

I agree that with a large leak even with the wastegate closed all the way to redline that it won't be able to make more a few psi, and that because of that there wouldn't be enough exhaust gas to spin the turbo fast. However if we had say a medium sized leak which is large enough that the boost will never reach 10psi (lets say 8psi for example is the max it can reach) would 8psi (with the wastegate closed) be enough to create enough exhaust gas to overspin the turbo? Assuming that if it spins faster trying to reach the 10psi and all the extra air is going out the leak it will just keep spinning faster and faster until it reaches the limit that 8psi can spin it to.

Gah this is doing my head in trying to understand it and explain it. I think the only real way to test would be to use a turbo tacho and a variable sized hole on the intake.

Edited February 4, 2010 by Rolls

[paulr33]

no, i dont think the physics would support an ever increasing acceleration of the compressor wheel

remember with a boost leak the engine is working no where near as hard, which means less exhaust gas

less exhaust drive, means lower compressor driver as well, so i think the turbocharger wouldn't be ever increasing its turbine shaft speed

[Rolls]

no, i dont think the physics would support an ever increasing acceleration of the compressor wheel

Obviously not forever but until it started to get out of its efficiency range I believe it would.

[JonnoHR31]

if its leaking enough to cause any damage to the turbo and you cant notice it then you shouldnt be driving a turbo car, simple.

[Rolls]

if its leaking enough to cause any damage to the turbo and you cant notice it then you shouldnt be driving a turbo car, simple.

It is just a theoretical question, I would hope that the average Joe would hear it and notice as well but that is not the point of this thread.

[paulr33]

i still dont think the physics would support it

if there is a leak on the intake side the actuator never opens so all the exhaust gas must run via the turbocharger wheel (instead of bypass)

so technically the turbine speed is ever increasing, but and it's a big but, the engine load is basically jack all, as there is no decent positive boost pressure forcing more load on the engine

[Rolls]

the engine load is basically jack all, as there is no decent positive boost pressure forcing more load on the engine

I agree with what you proposed if there is a very large leak. However if you decrease the size of the leak so that a decent amount of the air is going into the engine (remember a stock turbo can hold full boost at 3000rpm with half throttle, let alone redline on full) so let us say half the air is going in and half is leaking out. Now being as a stock turbo can run full boost at 3k with half throttle surely there would be enough exhaust gas to allow the turbo to keep increasing in speed to some point?

edit:

I've made the same thread over on performance forums to get a wide range of opinions and GTSboy has explained why he thinks it would overspeed with the aid of a compressor map. I guess the only thing to argue now is whether or not you have enough exhaust gas to keep the turbo spinning faster, personally I think with a small undersized (stock) turbo you would have no trouble doing this.

http://www.performanceforums.com/forums/sh...php?p=840645505

Edited February 4, 2010 by Rolls

[paulr33]

i think that it's either a non issue in the real world and its not common or the physics dont support it an ever increasing turbocharger shaft speed with a leak

theres no way either of us can prove it either way without a turbocharger shaft speed guage and some testing

garrett sell and recommend a turbocharger shaft speed guage to monitor the turbocharger shaft speed

maybe look into one of those if you are that keen and that precautious on it

i think there are more common elements that cause turbocharger failure in today's day and age

i would assume and logic would say so that the turbocharger is pretty well balanced and setup to maitain a higher than efficient shaft speed

for how long is debatable, but it would be at least able to cope with this for a short period

i think elements such as poor oil flow, oil contamination, excessive pressure surge from no BOV and compressor damage (from open mouth or poor pod filter) are your likely causes of turbocharger failure

[Rolls]

i think there are more common elements that cause turbocharger failure in today's day and age

i would assume and logic would say so that the turbocharger is pretty well balanced and setup to maitain a higher than efficient shaft speed

for how long is debatable, but it would be at least able to cope with this for a short period

Without a doubt there are, this is more just for some interesting debate, I'm running an AFM in my skyline now so it is not even a possible issue, I am just curious of the physics and whether it can occur.

I agree that we need a variable sized hole and a turbo tacho to ever prove this one way or the other, still I think it is interesting to discuss.

[paulr33]

understand

so are we trying to decide if the scenario is any different with AFM vs MAP?

or if its possible in either way to fry the turbo as a result of a leak?

[Rolls]

understand

so are we trying to decide if the scenario is any different with AFM vs MAP?

or if its possible in either way to fry the turbo as a result of a leak?

With an AFM I imagine the car would just run super rich and you'd notice straight away, unless of course the car was tuned from scratch with the boost leak. I wanted to get a better idea of whether the situation was possible with a MAP, I'm still not 100% convinced but I think it is quite likely, to what extent though? I do not know. Only way to tell is as you said, with a turbo tacho and a controlled environment.