SiRCiviC94

Quick? I have a B16a on a 57 trim garrett and a .68 exhaust wheel. if im driving around the city and hit anything from 1-4psi half throttlish and let off i get a chchchch sound and im not totally sure if its the turbo or the BOV but it would be nice to let a puff of air like most oem turbo cars do with atmopheric bov and not hear what i would call compressor surge. my old chinese turbo would surge a bit too but I didnt care about it and didnt bother addressing it since racing it worked perfect.

blow off is a blitz DD with what i believe the original spring stiffness. not race.

if i punch it and build say 5+psi steady and let off it works perfect.

let me know any idea's or if i should worry

TheShodan

iTrader: (14)

Its just a dual drive valve similar to the HKS. when you go just outside of vacuum like that, (0-5psi or so), they tend to flutter. No compressor surge. you're fine.

SiRCiviC94

superb. I did once check last year and could see the valve opening and closing simulating the surge and didnt worry then either. thanks for the re assurance. high boost coming soon!

TheShodan

iTrader: (14)

it can't "simulate" the surge. Surge is basically compressor wheel reversion in the opposite direction.

Forge Performance made an interesting explanation of compresor surge

"It is a surging or rapid change or oscillation to the speed or possibly even the rotational direction of the compressor wheel of the turbocharger when under load.

This is caused by one thing and one thing only, of which the origins of will be explain more thoroughly later. Compressor surging is caused by two opposing pressures acting against one another on the impeller and compressor wheels of the turbocharger which share a common drive shaft.

These two opposing pressures are exhaust gas pressure which spins the impeller wheel and then a reversion of boost pressure acting against the normal rotational direction of the compressor wheel which is driven by the impeller wheel.

The opposing pressures act on their respective wheels in pulses which are caused by intake and exhaust valve events (based on cam phasing, timing, and engine RPM). The opening of the exhaust valves within the head of the motor leads to exhaust gas pulses that spin the impeller wheel of the turbo which then drives the compressor wheel which generates boost. The pulses of pressure waves that revert back into the compressor wheel are similarly caused by intake valve events (opening and closing) however the buildup and subsequent reversion of pressure itself is caused by something entirely different. (See the next paragraph)

Though the term surging can seemingly imply many things in the world of turbochargers today, the term was originally derived from a condition in which the turbo (compressor wheel) is actually spooling and generating boost pressure faster than the motor can “ingest” it. In such a scenario, where airflow volume exceeds the rate of consumption at which the engine itself is capable of operating, as the compressor wheel is spooling and boost pressure is building, when it reaches a point at which the motor can no longer accept any more airflow, a buildup of pressure in the intake manifold and charge piping will occur that will cause the reversion of boost pressure (pulse timed by intake valve events) as the turbo attempts to overcome any and all flow restrictions.

The reason that the pulsating reversion of pressure into the compressor wheel is dictated by intake valve events and not by throttle position is that the forces (pressures) that cause surging are only present to act against one another at a high RPM wide open throttle condition in which the throttle plate does not act as a restrictor as it is fully open".


Forge continues:

"Compressor surging is incredibly difficult to empirically measure, however, through using a turbocharger turbine speed sensor (yes, they exist), it becomes possible to directly measure the speed of the compressor wheel under all kinds of different load and boost conditions, but because of the incredibly high speeds at which turbocharger impeller and compressor wheels spin and even gain and lose speed (accelerate and decelerate respectively), the highest sampling rate possible must be used as consistently as possible otherwise inconsistent wheel speed readings will result. Using a turbine wheel speed sensor to measure surging, however is not its primary function and not necessarily the best method which to do so, but it would certainly be the most accurate of any currently available option to measure such a phenomenon.

In order for such opposing pressures to even exist in order to be able to cause surging, the engine will need to be operating at a very high RPM, and the turbo too must be operating at a high RPM to be generating more pressure than the motor can ingest. A 200 RPM change or fluctuation in compressor wheel speed is not indicative of surging, particularly on turbochargers that can sometimes see wheel speeds in excess of 120,000 + RPM. Such a small change could easily be attributed to a wheel speed sensor anomaly based on sampling rate or even fluctuations in the volumetric density and speed of the exhaust gas pulses which are driving the compressor wheel by way of the impeller wheel. Even a 2000 RPM fluctuation in wheel speed is not indicative of surging to any degree. It would take a larger change in wheel speed, and more appropriately, a rapid oscillation of wheel speed more proportional to the maximum compressor wheel speed of the application to result in surging that would be noticeable or even detrimental to the turbo in any way."