So, I tried the GM BCS, as many users of evolutionm use it with success.
The car is an EDM EVO VII with EVO9 20G turbo, GSC S1r cams, full exhaust including elbow and DP, single cone air filter, 255lph fuel pump, 720cc inj, and 93 octane fuel.
I have installed the GM BCS in the stock location, with new tubes, and with a 1.5Watt - 5ohm resistance.
The goal was 22psi flat, without tapering, and it was achieved.
BUT from 3400 rpm to about 5000rpm there is a VERY FAST fluctuation, it look like surge (but it isn't surge). I can see it on my big and precise boost gauge, that I mount during the ecu calibration session, I can see it on 2byte load and 2byte airflow, and I can hear it!
I have tried with TBEC table set to zero, so no correction from the base wastegate duty cycle.
I have also tried with a MBC and i haven't the issue.


Anyone have had the same issue with the GM BCS?I have some ideas of how to solve, but I am curious to know if anyone has had the same experience, and how he solved.


WGDC table


GM BCS with TBEC set to zero, ISSUE


MBC, NO ISSUE

 

first off you could try removing the resistor since there are alot who didn't put a resistor and it is working fine and makes the bcs respond much faster(this is my set up as well). secondly i noticed that you used a 1.5watt. on evo_kid's thread on this he said 1watt. it might be drawing too much power.

if this doesnt work you could try borrowing a gm 3 port and swap that in. Good luck and keep us updated.

 

1.5Watt means that the max power that the resistance can manage is 1.5Watt.
I can put a 10000000000Watt, doesn't change nothing

However yes, a test is to remove the resistance, because it slows the solenoid, but many guys use 10ohm resistance, I use 5ohm, so I am in better situation than many others.

My GM 3 port is a new unit, and here in Italy it isn't so common to find one.

 

I'm the only one that have noticed this boost fluctuation?

 

I've noticed this too. I think it is the period of the duty cycle that is causing it. Since we can't change is, my idea is to try and take the boost source from after the IC. I also want to try one of those restrictors in between the GM 3 port and the wastegate to smooth out the pulses.

 

This is likely due to the on/off nature of solenoids and the lack of any substantial damping in the boost control lines. The ECU operates the BCS at a frequency of around 20 Hz, and when I did bench testing of several different boost control solenoids, I saw pressure fluctuations at the BCS that I figured would cause boost oscillations on a car, but up until now, no one had reported any oscillations.

The oscillations you are seeing don't have the correct frequency though. If I am reading your log correctly, I get a frequncy of 3.25 Hz which is much lower than the ~20 Hz operating frequency. Do your seat-of-the-pants observations of the boost fluctuations match the frequency in your log?

 

Hi mrfred, thanks for the reply.
I read your test, so I want to install a restrictor in the compressor line, and if it isn't enough another (bigger) in the wastegate line.
It will be great also if the 30hz patch can be made, to reduce oscillations.

I can hear a fast oscillation when I drive the car, but I don't think that it have a 20hz frequency. Maybe some of BCS oscillations are dampened in the line?
In a 5th gear log i can see a 4-6hz load oscillations frequency.

 

I wish I could say the restrictors will help, but my bench testing didn't show that much of a reduction in oscillations.

I think that tephra's v6 incorporates a 30 Hz frequency.

 

You'll never see the the "20hz" in the data logs cause the sample rate is not high enough. Some old guy named Nyquest said you need to sample a signal at least 2 times the highest frequency or you get aliasing, but really 2x is the absolute minimum. In reality you would want at least 3 or 4 times that to really be able to see it, so we need something around 60 - 80hz which I don't think we can get with EVOscan and MUTT.

I think adding some damping to the line will correct this. It is the worst for me at low RPM in 5th gear.

 

Most people log so many parameters in EvoScan that the effective logging frequence for each parameter is less than 10 Hz, so I was wondering if he was seeing aliasing. Hence the question about whether he could feel it.

There's not much that can be done to damp the oscillations with the high flow rate solenoids using restrictors and bleeders, especially if high boost and fast response is desired. I tried quite a few different restrictor and bleeder variations on the bench top, but the best that could be acheived was about a 20% reduction in oscillations. The most effective means to reduce the oscillations was to bump up the solenoid operating frequency.

 

What is the highest operating frequency you tried with the solenoid? Back in the day I made a home brew boost controller with a hc12 and a different solenoid off a GM car I found in the junkyard. I found the best I could get out of it was around 28hz, after that is was unreliable and would lock up under pressure.

I got some 555 timers and a FET, I could play around with this if I ever had time

 

With a base pressure of around 30 psi and 14 V applied to the circuit, the GM 3-port solenoid did fine at frequencies all the way up to the point where the frequency = 1/latency. I was able to monitor the performance by watching the voltage waveform on the series resistor using an oscilloscope. The Prodrive and the MAC solenoid did ok too, but the latency of the Prodrive had a noticable variability.