Same rpm, same throttle position, different airflow. The pipe effect on a misfire is very weak if it exists at all...
Attachment 332725
My graph doesn't show this well, but above 7k RPM the on-pipe and off-pipe air flow is too different, the on-pipe fuelling (what you've tuned for) will not support combustion off-pipe. Way too rich, true lambda probably around 0.5 or worse. As the engine speed falls below 7k rpm, the on-pipe and off-pipe air flow is not so different, true lambda is approaching the rich limit until it supports combustion. Once combustion begins the small increase of airflow from the pipe effect will bring the lambda above the rich limit, 'clearing' the cylinder. You could install any old MAF sensor to prove this.
I'm still working on the Ion sensing, but I'm getting impatient so I'm going back to measuring the pressure at the PV vent since that worked the best so far (I now have an adjustable bleed to atmosphere so I can adjust it's sensitivity), and using that input to try a table switching approach. Have a fuel table for no-pipe effect, and a fuel table that incorporates pipe effect. Theoretically I could put a box-style muffler on and tune 1 table, then put the expansion chamber on and tune the other. Pressure pulses will determine whether the pipe effect is active and ECU switches between the tables accordingly. Away from the pipe's effective rpm the tables should be more and more the same.
I'm thinking a box-muffler would provide no scavenging effect, and no return wave effect, can someone confirm that?
I'm also designing a 'pressure pulse' sensor. It's basically a piezo electric microphone hooked up to exhaust pressure, it will more accurately and quickly detect the exhaust pulse from the cylinder than the pressure sensor. I figure I can hear when the engine is firing clear as day, why not use a microphone...
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