Compressor fluttering coming on to boost
 

Hi all,

I have a freshly built cosworth motor and I've been trying to be good, but yesterday i decided to give it a little bit of a squirt in 5th.. and it built up about 13psi boost and it started to flutter (like a compressor stall sound) and didnt seem to want to build any more boost (im not sure how much boost it is set to run at this stage)

its a stage 3 cossie with a .48 t3/t4 turbo.

Would a weak actuator lead a to a problem such as this ?

Any help would be appreciated.
Cheers,
Damion

Too small turbine housing/large compressor. You`ve got surge!
Compressor surge is when the air pressure after the compressor is actually higher than what the compressor itself can physically maintain. This condition causes the airflow in the compressor wheel to back up, build pressure, and sometimes stall.

Normal compressor ratio of a turbo is 2: 1, ie the compressor wheel is 2.1 times the exhaust wheel, if you do indeed have a T4 COMPRESSOR but T3(.48) TURBINE, you will most likely have trouble in the form of surge, it stems from as said above.
At a given flow rate velocity and duct area vary roughly in inverse proportion to each other, and the dynamic head is prportional to velocity squared.
Very big differences alter the ADIABATIC ideal also so should be avoided as the sizes of the components is carefully considered when being put together.
A T4 compressor will not work with a T3(.48) turbine IMO.
In normal terms it is the turbine spins the turbo up but does not have enough puff/power basically to shift the amont of air from the compressor it is trying to shift.
Howver I am not convinced yet it is surge, need more details, does it come and go(surge) or does it just hit a wall and stay there ?
Surge tends to be slower in forming and is very linear, it could well be another fault, as you say actuator weak .
More info please.
tabetha

Thanks for the replies, It was seeming to come on flutter a little and then clear.. i haven't reved the engine over 5000rpm yet and i was not holding the throttle flat at this time.

I think I will play it safe for the next 500kms or so of 'running in' and then i will put the car on a dyno to check that all is well and then i will look into this problem further from there..

Could a restrictive air filter cause any issues here ?