gzk
9th January, 2013, 05:02 PM
hope this can help
http://www.megamanual.com/ms2/
For timing, we don't have a generator written yet. The basic principles are to determine a maximum advance for your engine and work backwards from there with heuristics ('rules of thumb'):
older engines (1960s up to 1990 or so) with two valves - max advance = 36?
newer two-valve engines - max advance = 30?
three or four valve engines - max advance = 26?
then adjust for bore size:
under 3.5" (89mm) - subtract 3?
between 3.5" and 4.000" (101.6mm) - no adjustment
over 4.001" (+101.6mm) - add 3?
then adjust for the fuel:
regular - subtract 2?
mid-grade - subtract 1?
premium - no adjustment
That gives us a maximum advance figure. It you have an aftermarket combination with a good squish area and optimized quench, subtract another 2?. If you have a flathead, add 3? or 4? or more.
We will use this to fill in the table at 100 kPa from 3000 rpm to the redline.
From idle to 3000 rpm, we want the advance (@100kPa) to increase fairly linearly from the idle advance to the maximum advance. idle advance is really a matter of tuning, but assume 8? to 16? in most cases, with stock engines being on the lower end, and 'hotter' engines being on the upper end.
So if we have a hot engine with 36? maximum advance and 16? idle advance (at 800rpm), the spark table might look like this for 100kPa:
100 16? 16? 18? 24? 28? 36?
rpm 600 800 1000 1500 2000 3000
Below 100 kPa, we add 0.3? per 1 kPa drop. So for example, if our total spark at 100kPa and 4000 rpm was 36?, the advance at 50 kPa would be:
36? + 0.3? x (100-50) = 51?
and the advance at 45 kPa and 800 rpm would be:
16? + 0.3? x (100-45) = 32.5?
However all of these would need to be tuned, and it often helps idle stability to limit the advance at idle to under 20?.
Finally, for boosted engines, you subtract 0.3? of advance for every kPa above 100 (it's not a coincidence that this is the same factor as for the 'vacuum' adjustments). Because 101.3kPa=~14.7psi, this works out to ~2? per pound of boost. It is often the case that you want to limit the retard under boost as well, typically so that it takes out no more than about ? of the maximum advance at 100 kPa.
None of these will give you the 'right' values for your engine though, and like the VE table calculator, are just a relatively safe starting point. They should be somewhat closer than starting with an empty table, though!
http://www.megamanual.com/ms2/
For timing, we don't have a generator written yet. The basic principles are to determine a maximum advance for your engine and work backwards from there with heuristics ('rules of thumb'):
older engines (1960s up to 1990 or so) with two valves - max advance = 36?
newer two-valve engines - max advance = 30?
three or four valve engines - max advance = 26?
then adjust for bore size:
under 3.5" (89mm) - subtract 3?
between 3.5" and 4.000" (101.6mm) - no adjustment
over 4.001" (+101.6mm) - add 3?
then adjust for the fuel:
regular - subtract 2?
mid-grade - subtract 1?
premium - no adjustment
That gives us a maximum advance figure. It you have an aftermarket combination with a good squish area and optimized quench, subtract another 2?. If you have a flathead, add 3? or 4? or more.
We will use this to fill in the table at 100 kPa from 3000 rpm to the redline.
From idle to 3000 rpm, we want the advance (@100kPa) to increase fairly linearly from the idle advance to the maximum advance. idle advance is really a matter of tuning, but assume 8? to 16? in most cases, with stock engines being on the lower end, and 'hotter' engines being on the upper end.
So if we have a hot engine with 36? maximum advance and 16? idle advance (at 800rpm), the spark table might look like this for 100kPa:
100 16? 16? 18? 24? 28? 36?
rpm 600 800 1000 1500 2000 3000
Below 100 kPa, we add 0.3? per 1 kPa drop. So for example, if our total spark at 100kPa and 4000 rpm was 36?, the advance at 50 kPa would be:
36? + 0.3? x (100-50) = 51?
and the advance at 45 kPa and 800 rpm would be:
16? + 0.3? x (100-45) = 32.5?
However all of these would need to be tuned, and it often helps idle stability to limit the advance at idle to under 20?.
Finally, for boosted engines, you subtract 0.3? of advance for every kPa above 100 (it's not a coincidence that this is the same factor as for the 'vacuum' adjustments). Because 101.3kPa=~14.7psi, this works out to ~2? per pound of boost. It is often the case that you want to limit the retard under boost as well, typically so that it takes out no more than about ? of the maximum advance at 100 kPa.
None of these will give you the 'right' values for your engine though, and like the VE table calculator, are just a relatively safe starting point. They should be somewhat closer than starting with an empty table, though!