Hello Pelicans!
I'm still slowly grinding on my 2.2T-2.4E engine swap, but I took advantage of a quiet morning to look deeper into my new ignition solution. I'm trying to grok how the stock vacuum input impacts timing. What's its purpose? Emissions? Efficiency? Idle control?
I'm aware that the original distributor works great without vacuum input, and so will the one I'm trying to set up, but I'm a curious sort and I want to understand.
I got a shiny new 123ignition programmable distributor (
https://123ignitionusa.com/porsche/) and am working on building ignition maps that match the Bosch original specs for 0 231 169 004. I was able to google the original data thanks to some very old Pelican threads and websites like
Early 911 Distributors - Carbs-Fuel-Ignition (CFI) - Repair & Sales
The centrifugal curve was very easy to reproduce. I know the advance is supposed to be anywhere between the lines, but for accuracy and performance I plotted the top line. If it's a bit too much, I can physically turn the distributor a degree or two to shift the whole curve down.
Here's the result. I'm very happy with it.
This is the original vacuum curve:
Using Google I was able to convert Torr to kPa, although I'm not at all confident with the numbers.
I don't like the result at all. When I try to use negative timing values the program gives an error. Also, in spite of the Torr to kPa conversion being rather straightforward, the values seem very low. For example, 200 Torr, the far end of the Porsche chart, is only about 35 kPa. The distributor recognizes inputs as high as 200kPa. I'm wondering if I'm missing a decimal point somewhere?
I'm also finding it confounding that 123ignition set an immovable point on the graph. The 100kPa, 0 deg is fixed and immovable. I don't think it's an issue because the vacuum range from Bosch is all far below that value, but I still don't understand why it's there.
So, vacuum system on the 2.4/2.7L engines... what's it supposed to do? Given the freedom to make the vacuum and centrifugal curves anything you want, where is there room for improvement? Anybody else fiddled with this system?
Thanks all!