I have been doing a little planning in terms of adding ignition control to the Megasquirt installation on my 1971 B20E. As part of this, I have been trolling the forums to try and get a sense of what people had been using for ignition control maps on the B20E. While doing this, I came across some posts that suggested that the B20E would run better without the vacuum retard function connected. Just run on pure mechanical advance with a range of about 8 deg to 32 deg (the mechanical advance on the B20E provides about 25 deg of advance on the crankshaft).
I decided to give this a try just because I was curious. I blocked off the vacuum retard line to the distributor and reset the idle down to around 900 RPM and confirmed the advance operation with a timing light. A little test driving with this arrangement showed no perceptible change in performance or drivability. I didn't do enough testing to determine whether there was any change in fuel efficiency with the resulting higher advance at low throttle openings. However, when I went to do a restart on the car with this arrangement I discovered that it had become very difficult to get started. The engine turned over without any problem and there were no misfires; however, I was having a problem getting successful sustained operation. Getting a start generally required wide open throttle like I was doing a flood clear. I reconnected the vacuum line to the distributor and the starting difficulty immediately went away. I repeated all of this twice to confirm that the starting problem was related to the disconnection of the vacuum line. With the current fuel set up that I have on Megasquirt combined with my Bosch SR437X starter motor, the engine is normally a very quick start up hot or cold.
I find all of this a little puzzling. Has anybody else experimented with disconnection of the vacuum retard on the B20E and did you experience similar results?
I understand the theoretical benefits (emissions issues aside) of running more advance at low manifold pressures. However, it seems that based upon my experience, I may need a very low advance setting in the cranking portion of the ignition map before transitioning to more advance in the idle section of the map.
I decided to give this a try just because I was curious. I blocked off the vacuum retard line to the distributor and reset the idle down to around 900 RPM and confirmed the advance operation with a timing light. A little test driving with this arrangement showed no perceptible change in performance or drivability. I didn't do enough testing to determine whether there was any change in fuel efficiency with the resulting higher advance at low throttle openings. However, when I went to do a restart on the car with this arrangement I discovered that it had become very difficult to get started. The engine turned over without any problem and there were no misfires; however, I was having a problem getting successful sustained operation. Getting a start generally required wide open throttle like I was doing a flood clear. I reconnected the vacuum line to the distributor and the starting difficulty immediately went away. I repeated all of this twice to confirm that the starting problem was related to the disconnection of the vacuum line. With the current fuel set up that I have on Megasquirt combined with my Bosch SR437X starter motor, the engine is normally a very quick start up hot or cold.
I find all of this a little puzzling. Has anybody else experimented with disconnection of the vacuum retard on the B20E and did you experience similar results?
I understand the theoretical benefits (emissions issues aside) of running more advance at low manifold pressures. However, it seems that based upon my experience, I may need a very low advance setting in the cranking portion of the ignition map before transitioning to more advance in the idle section of the map.