Can someone explain to me how a turbo ends up reaching the surge limit? I've read it's caused by too much boost relative to airflow capabilites, in layman's terms what does this mean and how would you determine from a compressor map if your likely to hit the surge limit.

I read in another thread that you half your calculated lbs/min required and at whatever PR(pressure ratio) used draw a line then see where both lines cross. I was looking at t04e 50 trim compressor map and at 2.0 PR and 15lbs/min I ended up left side of the surge limit. Only way I see to stay inside surge limit would be to run less boost(lower PR)?

 

What kind of power are you trying to make? 50 trim is relatively low boost pressure turbo. At 15 pounds of boost it won't be at the surge limit. Don't get caught up on boost pressure so much. Pick a hp goal and then ask what's best of that power level and what the car is going to be doing ie street drag auto cross etc.

 

I was just using that turbo as a example. Below is compressor map for that turbo. So say if I was running 1bar with this turbo(2.0PR) and my engine required 26lbs/min at half that i'm too far left of surge line. I'm not sure what the relevance is of checking half your required lbs/min at given PR but it was mentioned in thread I read regarding compressor maps.

 

Pressure ratio of two is going o roughly be 15 psi boost which lands you Roth in the effeceiency land on the map, your red line on the right. Where are you getting the green line from. At less boost it will come down on the angle of the map not like that. Also will probably be more like 32lbs/min at that pressure

 

Green line is 50%, this is what i'm trying to find out, what is the relevance of 50% as mentioned in this thread
http://www.sohchonda.com/forums/topi...ze-up-a-turbo/

 

This is going to come into play wich rather large turbochargers not with something of this size. I don't think I've ever had an issue with surge line and I've run upto a t67. When would you be at 59% half throttle? That would be less boost anyhow

 

Ok, just wanted some clarity on that and as to why you need to consider 50%.