Porsche SC 1983 Microsquirt setup for ignition control

[pw36889]

Hi there,

I wish to use the ignition control from Megatune to drive the ignition on my Porsche SC 1983 3.0 l engine. My timing and rpm signal is from the hall effect of the distributor. The ignition box is a MSD 6a + the associated coil. On the Megatune software, the base ignition setting is asking for the ignition input capture, the cranking trigger and the coil changing scheme. Can someone help me in setting those for my setup.

thanks

[Matt Cramer]

If you have a mechanical or vacuum advance, you'll need to lock that out. That said:

1. Ignition input capture with a Hall effect can be either rising or falling edge, generally whichever edge is closest to TDC.
2. If you can get the edge that triggers it to fall roughly in the 10 degrees BTDC range, use Trigger Rise; otherwise, use Calculated.
3. Standard coil charge and use the settings in the MSD page to get a 50% square wave signal. However, we do recommend using Going High / Inverted instead of Going Low / Normal with MSD boxes.

[cmonref]

pw36889,

If you have a stock 911SC distributor, you have a VR, not a Hall sensor. It is a VR if you have the 6-pointed rotating star below the rotor.

Matt suggested locking the advance out which will allow you to control timing thru MS. But as the timing advances, the rotor's position will lag its proper position under the cap -- MS will fire the ignition BEFORE the rotor gets into alignment. This will create weak spark transfer from rotor to cap causing the engine to suffer with weak spark. To avoid this, install a crank pulley setup to sense for the MS, and run spark thru a distributor that has functioning advance.

Brian

[pw36889]

Thanks for the response, I guess the correction on the advance from the MAP should be minor compare to CF correction. In fact I ran the engine with and without the vacuum hose in the distributor and I got circa 3 deg. I think with proper mechanical adjustment I should be able to make it work. I let you know once I've got results.

Thanks

Alain

[cmonref]

Here is the writeup that provides more detail than I summarized above, describing the author's plan -- the same as your plan -- then what he found and how he fixed it.

http://forums.pelicanparts.com/showthre ... t=ignition

Brian

[pw36889]

I am not tto sure that I will remove the CF compensation device on the distributor in my case like Tony has done. This will require to have at least 30 deg of of contact from the rotor to the contact pin on the cap. I am not sure this will work out. I rather use the CF device and compensate for deltat with the mapping. I will try to make it work this weekend and let you know the outcome.

Alain