To Vacuum Advance or Not to Vacuum Advance
I don't have any data logs with a drag race start.
But it really doesn't matter. Manifold vacuum increases only a little with rpm.
(The logger is reading MAP and I've converted it vacuum. Its about an 1"Hg different than I see on the dash gage (mechanical).)
Here's a short WOT onto an interstate from a rolling start.
Dark blue is vacuum. Orange is acceleration, Green is rpm.
Next is one to give some idea of what happens when running a restricteed carb.
This is on a dyno, the dashed lines show a run with just two barrels of "750" on a 340.
Rolling into WOT in 3rd gear (torqueflite).
First marker: 3970 rpm, 2.2" Hg
Second Marker: 5740 rpm, 3.5" Hg
Pretty unusual for a vacuum advance to add anything down around 3"Hg.
The one on my FSJ does. AMC 360, smogged, with a 2 bbl (Motorcraft). Believe me - I've never spun it to 5500 rpm!
But at WOT its way below most vacuum advances.
I don't have any data logs with a drag race start.
But it really doesn't matter. Manifold vacuum increases only a little with rpm.
(The logger is reading MAP and I've converted it vacuum. Its about an 1"Hg different than I see on the dash gage (mechanical).)
Here's a short WOT onto an interstate from a rolling start.
Dark blue is vacuum. Orange is acceleration, Green is rpm.
Next is one to give some idea of what happens when running a restricteed carb.
This is on a dyno, the dashed lines show a run with just two barrels of "750" on a 340.
Rolling into WOT in 3rd gear (torqueflite).
First marker: 3970 rpm, 2.2" Hg
Second Marker: 5740 rpm, 3.5" Hg
Pretty unusual for a vacuum advance to add anything down around 3"Hg.
The one on my FSJ does. AMC 360, smogged, with a 2 bbl (Motorcraft). Believe me - I've never spun it to 5500 rpm!
