4x4

what is it?

and what does it look/sound/smell like?

cheers

mechanic28

iTrader: (5)

pretty sure this is where the turbo is forcing to much air into the engine,therefore the air has no where to go and makes the turbo stall!as for what it sounds like aint got a clue!

4x4

so this would be going on when your on the power yes??? not when you back of?

mechanic28

iTrader: (5)

yes when your under boost conditions

bluescortcossie

as a understand its when the turbo is producing more air than the engine can consume so the extra air is forced back through the turbo which then makes enough room for it to be produced again and then starts all over again , this causes a sort of fluttering noise due to the air pulsing

as for sound its a bit like wastegate chatter but with on boost noise too

i may be miles out with that theory though

bluescortcossie

its most noticeable on big tractor pulling engines that use stupidly big turbos

http://www.youtube.com/watch?v=mHmdO350xcY

4x4

see now this is good... the reason for my question is because I like yourselves had the same theory for comp surge but these dumb jap car owners i know always say "aargh look that cars got comp surge" every time they hear turbo chatter after a driver has just slammed the throttle shut just after hitting high boost.

i always argue with them on that but to no avail

"i seriously hate MOST jap car boys... and even if im wrong i still hate them!!!

if i am wrong someone please correct me

Bullett

iTrader: (2)

stu is best to explain this.i thought it was wastegate flutter?i was told it was the same thing

Stu @ M Developments

iTrader: (12)

Brief explanation:
Surge is caused by stall, which is worsened by surge, its a vicious circle...

Imagine the way our turbocharger's compressor is driven, right back to basics: The turbine wheel is spun by exhaust gas, utilising also the energy stored in the exhaust gas as latent heat.

This force on the turbine shaft generates torque at the compressor end as they are physically connected. Remember that part as its the key element.

Ok,
Now lets imagine our turbocharger compressing air, forcing it into the engine, the engine is utilising it.. what happens then? Ok, The engine expells it, and our turbine housing pressure goes up accordingly, the torque applied at the turbine wheel increases, increasing the spin speed and compressor efficiency at the other end. Great chain of events!
End Result? boost is climbing nicely.

Ok,
Now imagine this scenario:
The turbo begins to spin, as above, but the compressor wheel is generating more air than we can move and the torque required to spin that huge compressor is not being met? Remember that unless the air is processed by the engine, and expelled as hot, rapidly moving air into the turbine housing, our turbine shaft torque will not increase to spin the compressor faster, and it may well diminish.. our compressor is slowing, braked massively by the compressed air its trying to overcome and increase.....

Result? Compressor starts to slow a little.. (beginings of a compressor stall)

Ok, So now what?
The engine is still rotating and consuming air, but the turbo has stopped producing an excess, so our engine has now had chance to consume what excess was available and the inlet pressure is now diminishing, the turbine torque is now increasing again...

VERY IMPORTANT:
Remember also that at same time, compressor resistance to spin has also dropped due to housing no longer being as pressurised and as a result, the torque required to spin it has dropped massively..

Boom.. Suddenly the Turbine wheels torque massively exceeds the compressors resistance and the turbo spins to speed in an instant!! Sounds great, rapid boost climb!! The compressors acceerating at over 2G

BUT: We just hit the same problem again, our huge compressor has made so much boost, so fast, and is trying so hard to push the massive volume or air, that our YB cant use it.... so we start to slow again........

So we went: Fast, slow, fast, slow, or in other words: The turbo is Surging. As you can imagine, it continues this cycle until it hits the revs your engine consumes all the air.. then your away!!

Downsides to this surge are pretty obvious:
We can have serious bearing wear, due to the excessive loads imparted on the shaft supports. Compressors have been known to simply explode!!

Worst case scenario, the compressor being slowed rapidly with a turbine still trying to accelerate it can simply do as expected, part company.

Hope this helps to explain in as simple terms as i can put it, the phenomena known as "Turbo Surge."

When you back off, the chattering noise is a similar phenomenon, so the jap boys are almost right, but its NOT what we would call classic surge as your only really interested in surge when your on the power and TRYING to consume air. You arent trying to consume air at all with a closed throttle obviously.

Bullett

iTrader: (2)

so is this more than likely how i snapped my standard t3 shaft in two at 330 bhp stu?

R5FORD

iTrader: (1)

nice explanation Stu

bud-weis

very doubtful i'd have thought?

Lo@der

iTrader: (8)

Well done stu, I even understood that.

R5FORD

iTrader: (1)

agreed. sounds doutful tbh. how much boost were you running?

Bullett

iTrader: (2)

its the one and only turbo ive broken.and ive had turbo'd cars for ten years. never did understand how i snapped one.

4x4

Stu @ M Developments

thanx for the detailed explanation... very helpful and very useful.

i also understand what you mean when backing of the throttle is a form of surge but like you say we are not interested in it unless we are on the power trying to go fast!

Thanx again, good explanation as always

Mr.T

http://www.youtube.com/watch?v=LZUbo_mNDZM

Bullett

iTrader: (2)

round 20 to 22psi from what i remember