The way i understand it, surge is when the turbo produces more air than the engine can consume?

is this right?

also i have heard that some turbos are more prone to surge than others, if this is true, why?

 

Yes, as far as i'm aware.

I wouldn't think any turbo is more prone to surge than any other. The turbo surges if its incorrectly spec'ed for the engine.

 

yes, being very basic

yes and some turbos are more susceptible to surging, due to there design,, normally a too small of exhaust housing compared to the compressor

 

ahhh, i can now see the picture in my head...

turbo produces so much pressure (as the engine cannot consume more) and the exiting exhaust gasses do not have enough force to spin the turbo?

 

This only happens mainly on the smaller turbos mainly GT3071 or below, The Larger units like a GT35 can run the .63 without a problem, Surge on these is down to airflow.

Mark

 

Ah, that makes sense. It will have a lower boost theshold with a smaller exhaust housing?

 

my car was surging very badly when i got it. its a t4 to stop surge boost was caped to 22 then 26 psi below 5400 rpm then after that it runs 32 to the limiter and loves it. the surge was so bad before set up it was jumping up and down about 8 psi on the gauge

 

change the word pressure for flow, and ill be happy

 

but as the engine cannot consume it, its not flowing? therefore pressure?

 

turbos produce flow,, pressure is force acting on an area! so therefor the engines isnt consuming the flow

 

sorry Gareth you clearly know what you are talking about, unfortunately the turbos i work with are a bit bigger and the terminology doesn't quite read across, but i think i get where you are coming from buddy

 

Surge line is one the left:


If you dont know how to read a compressor map, look here:
http://www.vauxhall-sport-forum.com/...urbos-t92.html

 

sorry Chip, do you a plot for a BR710, RB211 or T1000, as i dont know much about the one you posted

 

Surge is NOT as described but when the COMPRESSOR side cannot produce ENOUGH airflow, due to bad ratio between TURBINE and COMPRESSOR sizes.
The surge effect is caused by the air speed stalling due to not having enough power transmitted through shaft to drive it sufficiently hard, due to amongst other things too large a compressor side unable to build boost, which is continually being used.
All turbo's have a window or engine load/rpm where they operate best, below this pointy you can get a surge situation whereby the flow is unstable due to the turbo not being able to supply enough air.
When the mass flow rate through a compressor is reduced while maintaining a constant pressure ratio a point is reached where local flow reversal occurs in the boundary layers, if the flow point is further reduced complete flow reversal occurs.
This will relieve the adverse pressure gradient until a new flow regime is established at a lower pressure ratio, the flow will then build up again to the initial condition and this flow instability will continue at a fixed frequency and can be quite violent and is called surge.
It is more prone on turbo's that have a small operating window.
Put simply there are various reason for surge but most common is bad match of comp/turbine housing sizes whereby the shaft connecting the two cannot transmit enough force through to the compressor side due to compressor being to large, and power transmit not being great enough from turbine impeller.
tabetha