IE when people say 'He came round & out of that last corner surging his tits off!'

 

Stu did a REALLY good explanation the other day....

Use the force Luke!!!!

(or try the search button you CUNT)

 

think its when the turbo is supplying too much air for the engine to consume

dunno if i read it in one of stu's technical essays or not .. i might just be dreaming it

 

Its far too early Lee!!

 

I'll have a look Pete, thanks!

 

Brief explanation, starting back at 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. Torque.

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."

Taken from this topic:
https://passionford.com/forum/viewtopic.php?t=34511

 

Nice one Stu.......

 

So what you trying to say ????






















Good explanation Stu
I dont know how you can be arsed to type all that , but its good that you do

 

take it i was wrong then well not exactly right in what i put

thanks stu

 

What is slightly misleading, is when not running a BOV and letting off the throttle, the fluttering noise of the boost going back through the turbo is also sometimes called 'surge', but it is not the same occurrence as Stu said above as there is no loading on the turbine shaft..

 

To elaborate a little further...

Whilst there is no loading on teh shaft with the throttle closed, the compressor stall was initiated at around 60% throttle when there was indeed still a load on the shaft. Of course once closed and turbine effort reduced to nil, the pressure trapped in teh induction system still needs to equalize with atmosphere at one end and depression at the other and we hear this happening as a warbling effect through the compressor which, whilst slowing, is still travelling at very high speed.

 

No what you put, although over simplified was indeed correct.

 

should have asked your Mrs Franco

she knows all about SURGE

 

Indeed she does!!

I may only have a 4 in penis...............

But i've got 19stone of muscle to ram it in with!!!

Now back on topic Mike!

 

19 stone

 

I take it you'll know while giving it beans if the turbo's surging

What are the main causes for this then........... Mechanical failure?

 

I know i hide it well!

 

spat me tea out at that



so running a bov is in someways a good idea .. if you could get it to open and close at specific pressures, it would remove the excess pressure but not enough to stop the turbo totaly stalling, thus allowing a faster spool up time.. i think ..

 

Its sounds like "wastegate chatter" but at full boost full throttle instead of as you back off.

The reason is an incorrectly matched turbo/engine combination essentially, its nothing to do with mechanical failures.

Typically its when someone has a turbo with a big compressor side for huge power but tries to get it to spool up quickly by having a small hotside on it.

 

Cheers chip!

So bad forward planning is the biggest culprit for surging

PS

Pete.........sorry mate!

 

To a certain extent a good mapper can minimalise the effects, but yes if you get the right turbo in the first place, its not an issue.

 

Yes, you need an ecu with electronic BOV control, so the valve can be opened a certain amount, on/off or pulsed and above and below certain boost/rev threshholds..

 

I remember seeing JC at National day last year with surge, the sound is wierd, like forced chatter,as chip put