Knebel
Senior Member
I am not sure how to properly ask this but can someone explain to me, lets say I have a mechanical timing curve that is only rpm dependant, how do i know how many degrees the vacuum adance should add and when?
In Theory:
If i break this down, a regular distributor has so to speak different "steps" of advance. anything above idle, when the throtte opens is purely mechanical advance until it maxed out at "all in at 3000rpm". We reach this point and back off the throttle and the vacuum goes up and adds more advance to it.
no vacuum advance connected would that look like: idle 18° - 1500rpm 20° - 3000rpm 34°...or something to that affect
lets say I add vacuum adance to the picture, I know that I want to reach 40 or so degrees at cruise, which would be the all in at 3000 (34° plus 6° vacuum). But...how is the mechanical plus vacuum determined at rpms below "all in rpm". Lets say we are just above idle or cruising at 1500rpm and are having 20° mechanical timing, should the vacuum advance only be adding...2... 5° or whatever it takes to reach the 40+°? If in theory it would be adjustable that high?
What is the optimum timing at rpms below the 3000rpm threshold while no load is applied, which of course will have lower mechanical timing? Would you aim at 44° while coasting or cruising at any engine-speed below 3000?
would a cruise/coasting situation look like: idle 18° -off idle rpm cruise 44° - 3000rpm cruise 44°?
how do I determine how many degrees the vacuum advance SHOULD add between maxed out and not activated at certain rpms? Im trying to understand a little how a vacuum advance is normaly working and if (in building a timing curve) it can be improved with the abilities I have in my EFI. I am focusing on cruise timing values and am very unsure what to do about low load/low rpm situations. So think about it this way, if you could punch a number into the vacuum advance and it would add whatever number you put in, what would you do?
In Theory:
If i break this down, a regular distributor has so to speak different "steps" of advance. anything above idle, when the throtte opens is purely mechanical advance until it maxed out at "all in at 3000rpm". We reach this point and back off the throttle and the vacuum goes up and adds more advance to it.
no vacuum advance connected would that look like: idle 18° - 1500rpm 20° - 3000rpm 34°...or something to that affect
lets say I add vacuum adance to the picture, I know that I want to reach 40 or so degrees at cruise, which would be the all in at 3000 (34° plus 6° vacuum). But...how is the mechanical plus vacuum determined at rpms below "all in rpm". Lets say we are just above idle or cruising at 1500rpm and are having 20° mechanical timing, should the vacuum advance only be adding...2... 5° or whatever it takes to reach the 40+°? If in theory it would be adjustable that high?
What is the optimum timing at rpms below the 3000rpm threshold while no load is applied, which of course will have lower mechanical timing? Would you aim at 44° while coasting or cruising at any engine-speed below 3000?
would a cruise/coasting situation look like: idle 18° -off idle rpm cruise 44° - 3000rpm cruise 44°?
how do I determine how many degrees the vacuum advance SHOULD add between maxed out and not activated at certain rpms? Im trying to understand a little how a vacuum advance is normaly working and if (in building a timing curve) it can be improved with the abilities I have in my EFI. I am focusing on cruise timing values and am very unsure what to do about low load/low rpm situations. So think about it this way, if you could punch a number into the vacuum advance and it would add whatever number you put in, what would you do?