Just thought I'd post up a quick note about something I did recently that worked out well.
I was wanting to optimise ignition timing for cruise, so using some switches on my dash to trigger a combination of datalogging, 4D ignition, 5D ignition and the 2nd ignition table set to overlay mode.
With the idea that I could add or remove timing from the main table in varying amounts without having to stop the car, and datalog the whole lot easily.
Since you can turn on more than one ignition trim table at once, using those three you can get a combination of timing settings which I then marked on the switches.
So +1 degree, + 3 degrees, +5 degrees, etc.
I completed a run on a particular stretch of motorway that has lots of ups and downs, with cruise control turned on at a speed that's at 3250rpm in 6th gear.
Then flicked the first switch, did it again.
Flicked second switch, did it again, and so on.
When home looking through the data, bringing up a time plot with instant fuel consumption and throttle angle it was very easy to see which timing gave best economy.
However a secondary method of checking fuel consumption overall is to create a "statistics" page and bring up wheel speed and instant fuel consumption, and look at the mean values:
Then from here I've made a quick excel sheet that converts it to Litres per 100km:
Then from here, collated the results from each run.
So based on this it's pretty clear that an additional 9 deg advance made the engine pretty happy on those particular cells, so updated my ignition table and readjusted some of the surrounding cells to more sensible values too.
It was a fairly time consuming exercise but it's amazing to see how much fuel I have been throwing down the toilet just based on under advanced ignition.
It was also interesting to see that at 100kpa my car only has 14 deg ignition at that rpm, but then by 70kpa it's wanting 33. (The goal AFR changes though, to be fair... 15.2:1 goal AFR for cruising)
Since changing the timing the car is a lot quieter too!
I am guessing because when you dont have enough timing, the flame front is still expanding when the exhaust valves open. So instead of having energy push the piston down, it's coming out the exhaust as noise and heat.