using MSD graphview for vacuum advance
04-13-2010, 06:31 PM
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using MSD graphview for vacuum advance im having trouble with my curve for vacuum advance. i know what i want in In Hg vacuum, but the measurements on the graph are in PSI. i don't know what values i should put down. the stock graph went from top left to bottom right, the way i want it in vacuum, it goes from bottom left to top right... what's going on?
04-13-2010, 08:39 PM
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well i figured that since 1 in hg is 0.4912 PSI i would do that, but i want to be sure since my curve looks exactly opposite of the factory one. why would they have 20 degrees advance at 0 psi/in hg?
04-14-2010, 06:19 AM
#6
0 PSI is 30 inches of vacuum. High vac is what you see at idle/low load cruise.
With the engine off the MAP sensor should read atmospheric pressure, roughly 15 psi. Motor heads call that 0 inches of vacuum. Run the engine and pressure in the manifold drops. A vacuum gauge measures the difference between manifold pressure and atmospheric pressure. As vacuum goes up, MAP pressure goes down.
Got it?
I use to have a link to a table saying stuff like 12 inches vac = 6 PSI absolute, but can’t find it anymore.
MSD should have an option in their software to do an approximate conversion.
With the engine off the MAP sensor should read atmospheric pressure, roughly 15 psi. Motor heads call that 0 inches of vacuum. Run the engine and pressure in the manifold drops. A vacuum gauge measures the difference between manifold pressure and atmospheric pressure. As vacuum goes up, MAP pressure goes down.
Got it?
I use to have a link to a table saying stuff like 12 inches vac = 6 PSI absolute, but can’t find it anymore.
MSD should have an option in their software to do an approximate conversion.
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04-16-2010, 05:34 AM
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http://www.carcraft.com/howto/ccrp_0...arts_cost.html
page 2 has the conversion info. Hope this helps
CONVERSION TABLE
Pressure in psi absolute Inches of mercury
5 10.2
10 20.3
15 30.6
Ignition Curve Basics
Basic ignition timing can be a bit confusing, so let's dig into the meat of all this to make it less intimidating. We'll start with initial timing. This is indicated on a timing light on the harmonic balancer with the engine at idle. For most performance engines, initial timing is around 10 degrees before top dead center (BTDC). Next, we'll address mechanical advance. Most mechanical-advance distributors can generate around 25 to 26 degrees of total mechanical advance. This is created by a pin moving in a slot in the advance plate of the distributor controlled by a combination of weights and springs. When you add an initial-timing figure of 10 degrees with 26 degrees of mechanical advance, you get a total advance of 36 degrees.
page 2 has the conversion info. Hope this helps
CONVERSION TABLE
Pressure in psi absolute Inches of mercury
5 10.2
10 20.3
15 30.6
Ignition Curve Basics
Basic ignition timing can be a bit confusing, so let's dig into the meat of all this to make it less intimidating. We'll start with initial timing. This is indicated on a timing light on the harmonic balancer with the engine at idle. For most performance engines, initial timing is around 10 degrees before top dead center (BTDC). Next, we'll address mechanical advance. Most mechanical-advance distributors can generate around 25 to 26 degrees of total mechanical advance. This is created by a pin moving in a slot in the advance plate of the distributor controlled by a combination of weights and springs. When you add an initial-timing figure of 10 degrees with 26 degrees of mechanical advance, you get a total advance of 36 degrees.
Last edited by 70lx327; 04-16-2010 at 05:35 AM. Reason: want to
04-16-2010, 05:37 PM
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that's how mine is. that's how many people set the curve up on a mechanical distributor as well, but they don't have the luxury of the real low initial timing setting unless they have a start retard.
04-16-2010, 09:06 PM
#13
http://www.carcraft.com/howto/ccrp_0...arts_cost.html
page 2 has the conversion info. Hope this helps
CONVERSION TABLE
Pressure in psi absolute Inches of mercury
5 10.2
10 20.3
15 30.6...
page 2 has the conversion info. Hope this helps
CONVERSION TABLE
Pressure in psi absolute Inches of mercury
5 10.2
10 20.3
15 30.6...
04-16-2010, 09:25 PM
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the graph you showed is how the map vacuum advance is supposed to be set. supposed to start on the left high, and as map increases (vacuum decreases) the timing should be pulled. like this:
http://www.carcraft.com/howto/ccrp_0.../photo_07.html
http://www.carcraft.com/howto/ccrp_0.../photo_07.html
04-17-2010, 08:26 PM
#15
the graph you showed is how the map vacuum advance is supposed to be set. supposed to start on the left high, and as map increases (vacuum decreases) the timing should be pulled. like this:
http://www.carcraft.com/howto/ccrp_0.../photo_07.html
http://www.carcraft.com/howto/ccrp_0.../photo_07.html
04-18-2010, 11:35 PM
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dude look at the picture i send you again. look at the TOP graph, not the bottom. the bottom graph is rpm, the top is MAP. to the left of the graph is 0, to the right is 15. it starts off high and goes lower as MAP increases...
04-19-2010, 08:10 PM
#19
