I will answer your questions the best I can but I will start off saying that using a MBC on a modern car that can be tuned easily is in my opinion not a good plan.
MBCs depending on how it has been plumbed into the system can cause all sorts of different results. Ultimately you can use them to set boost but temps, altitude, humidity, etc all will cause the boost to fluctuate.
So you mentioned that your seeing more lag slower response etc. My GUESS is that the wastegate actuator is seeing some signal prior to target boost being hit. In short the wastegate is cracking open too soon, this is causing slower spool and a feeling of lag or heavy throttle response. Again depending on how the MBC is actually in the system will make a difference it how it works and responds.
The way to solve your problems would be to install and tune a 3 port EBCS like a Grimmspeed one. Allowing the car to handle boost control will keep safety systems in place to protect the motor and will compensate for climate changes and always hit your targets.
Originally Posted by justinh
Just recently bought an 05 sti with an fp green (recently built motor + all supporting mods) that was tuned to hit 1.6 barr. The weather in my area is a bit cooler than where the car was tuned by the previous owner and have noticed that i am having spikes of overboosting around 1.7 1.75 barr in higher load situations (higher gears, even cooler weather, sometimes partially being on the throttle when shifting, etc). The car only has a MBC (hallman pro) and accordingly i turned down the controller approx a 1/2-3/4 turn to attempt to keep the boost down.
Immediately i noticed that the throttle is less sensitive and that there is more lag in building boost, yet i am still managing to reach 1.7+ barr
1) why is it that despite turning down the controller i am still achieving the same boost levels?
2) is it normal to have the increased lag and decreased throttle response issues when turning down a MBC?