As some of you knew, I had a nasty little boost overrun. It wasn't so bad when creeping into boost from say, 3k. But when shifting at 5-7k and matting it, I'd get an over shoot of 5psi before it settled. Well, I was playing around with the software last night and I stumbled upon a little tidbit. I was running my BCS at 50hz. Not good since 15-20hz is reccommended. I've got it at 17psi now with an overrun of <2psi when shifting from the upper legions of the rev range. This seriouly has made my day. This would have been nice to know ON SATURDAY!!!!!! Now all I need is that 7 bar MAP sensor, and all hell is gonna break loose :nana:
Awesome.... its great you are learning all this stuff with Link so you can help me with my car when it comes time
So what is a BCS? Boost Solenoid? If so, sounds a bit strange that you turn down the sampling frequency and get a decrease in boost....do you think that maybe something is being missed? Maybe nothing, but thought I would note that this didn't sound right.
When I think about it, it kinda makes sense. With a lower frequency, the pulse widths are longer overall, even though there are less per given time. Therefore, when the turbo is spooling up very quickly, like when I'm ripping through the gears and the turbo goes from zero boost to target at 4-5krpm, the longer pulse widths have more of a chance to act upon bleeding boost pressure in the Boost Control Solenoid. With the higher frequency, there was more dead time in the BCS's activity and thus was slower to react to the differntial boost gain. [/nerd]
I see where you are going, but that would be valid if the duration of the acceleration was on the order of the frequency of the controller. Over a "long" time, relative to the duration (duration of one cycle is 1/Freq), the amount of time that the valve is open is equal. The "time" you need is how long it takes for the engine to get from 0-4k rpm...maybe 1.5sec? In 1.5sec, the solenoid would have cycled (open and closed) about 75x on the high freq and ~30x on the low freq, I would call that "long" since it is happening more than 10x for both freq. However, the amount of time that it is open would be the same. Maybe the solenoid can't open and close at 50Hz? If that was the case you would have to understand how the solenoid reacts to the controller. It may just miss cycles on a periodic basis or it may completely confuse it and it may open randomly... [/biggernerd]
Ya, 15-20hz is reccommended because, "higher frequencies can cause erratic operation." The thing is, the BCS worked fine once the boost settled, was was plenty stable when slowly working into boost, like on the dyno. The problem was only when shifting in the upper RPM regions, and matting the pedal. The boost would ramp up so fast, it seemed that it took a half sec for the BCS to catch up. With the lower frequency, the solenoid is more effective at steady state. When I first lowered the frequency, my boost was 3psi higher without changing the duty cycle. I'm thinking you are on to something with that the solenoid just could not open and close at 50hz. I gues that is kinda was what I was getting at, but didn't word it right. By running it too fast, it must have been too short of a pulse width for it to be as effective at it should have been. Now I'm wondering what is a better solenoid. My GM, or the one I was running which come on the old turbo Legacys. That older solenoid is apparently better than the ones of late on the WRX and so on. The ports on it are pretty big. Maybe a little experimantation is in order...
I think that you have found the culprit.... As for a solenoid with a bigger port, based on logic alone, that would result in issues at higher freq (more cross-sectional area to open/close). However, logic isn't always right... Good luck....
