If Christian is or has any experience with the gt28 on the ms3... please post up what size pill you are using. The hole in mine has a .035" hole. Using the Standback set to 20psi. I am spiking to maybe 21-22psi before I settle into 19~20 psi gear pending. I think I tried .065", but could never hit my targets. It was set to 18psi and only hit maybe 14psi.
This is very simple, but will take a bit to explain.
Mechanical Tuning
Changing the size of the center hole in the restrictor pill; the vacuum lines for the factory boost control system contain a small brass restrictor pill located in the short vacuum line coming off the turbo compressor housing. In the MS3/MPS, this restrictor pill is actually pressed into the compressor outlet vacuum nipple. The middle of this restrictor pill has a lengthwise hole precisely machined to a certain specification so that it works with the factory wastegate actuator and the wastegate duty cycle settings in the stock ECU. The size of this center hole can be changed in order to mechanically assist boost control.
A smaller diameter hole in the center of the brass restrictor pill will have a higher tendency to create boost spike in the system and require less wastegate duty cycle to run higher boost. The larger the diameter hole in the center of the restrictor pill, the less chance the boost control system will boost spike and greater wastegate duty cycle will need to run in order to produce higher boost. If you have a stock turbo and are running an AccessPORT map, you have no reason to modify your restrictor pill. If you have installed a new turbocharger and you are using the stock boost control system to tune boost, please verify that the vacuum line coming off the turbo compressor housing (prior to the T-fitting) contains a restrictor pill with a hole machined in the center of the pill.
The stock boost control system most commonly uses a restrictor pill with a center hole size of 0.041 +/- 0.001.
So...
The weaker the WG actuator daiphragm, the smaller hole in the restrictor pill. A 7psi WG actuator needs a restrictor pill in the .030" - .040" range.
The stronger the WG, the larger hole in the restrictor pill. A 16psi WG actuator needs a restrictor pill in the .041" - .058" range.
If you are increasing or holding wastegate duty cycles steady and boost is dropping then you have most likely reached the threshold of the mechanical efficiency of the turbo or your exhaust gas back pressure prior to the turbo is too high and is forcing the wastegate valve to open.
Generally speaking,
you should not try to get a 7psi WG actuator to control boost above double its base pressure or 14+psi. Boost control is less stable as you go over double the base WG pressure. If you want to run higher boost, then start with a strong WG actuator.
If you are increasing or holding wastegate duty cycles steady and boost is dropping then you have most likely reached the threshold of the mechanical efficiency of the turbo or your exhaust gas back pressure prior to the turbo is too high and is forcing the wastegate valve to open.
If you are having a small boost spike you may need to decrease the WGDC percentage a few hundred RPM prior to the over boosting event to allow the exhaust energy to be released past the turbine wheel.
NOTE: With porting a wastegate, you are trying and make the wastegate valve function potentially work better which means that your turbo is going to lower boost super fast when the wastegate door/valve opens or not run as much boost as it was engineered to. If you make your wastegate react quicker then boost will be very difficult to stabilize and reach peak #s at an earlier RPM. If you make the wastegate flow better, then the exhaust energy your turbo needs to make and maintain boost will have less opportunity to flow across the turbine wheel. Generally speaking, air/pressure/exhaust gases will always flow along the path of least resistance. Not bashing, just trying to give you a different perspective. I hope this helps.
Take care,
Christian.
