[MethoD]

HFS4 connected to a Link ECU. The Link provides a PWM output to the HFS4. I use a table with RPM and MAP as X and Y axis to control the duty cycle of the output. I have the flow meter output from the HFS4 also connected to the Link. I use the value from the flow meter as an axis on fuel trim and timing advance tables. Thus the greater the flow, the more fuel is pulled and the more timing is advanced (to a limit, of course).

I'm still in the process of tuning the system. It's slow going because I only make small adjustments then do several pulls to verify AFR is safe and no knock, but so far it seems to be working out pretty well. The one thing I notice though is that the longer the meth sprays, the richer the AFR becomes. It does seem to stabilize after a few seconds. I'm assuming that is because the first few seconds some of it wets the intake piping. The upshot is that the tuning has to be a bit of a compromise -- if I don't pull enough fuel out, it gets too rich in the upper gears. Pull too much out and I get lean at first.