After my issue with a fluctuating vacuum tester, I wanted to learn more since part of my problem with my turbo Busa this summer had to do with the vacuum connections. After some searching and reading, I came up with the following since I'm interested in making a few changes. I certainly hope the following is correct so please let me know and feel free to add to this...
Vacuum at any given cylinder is only created during the intake stroke, or once every 4-strokes, which explains the wild fluctuation after connecting the vacuum tester to just one TB.... one stroke with vacuum followed by three strokes without vacuum. Using all four throttle bodies smoothed out the response since there was always one cylinder providing vacuum.
Apparently using vacuum ports from any two TB's won't necessarily give the same results... for example, pairing TB's 1&2 can have a different effect than pairing TB's 2&3. I'm sure someone else can explain this better than me... and feel free to do so...
During one intake cycle, using the vacuum ports from TB's 1&2 will provide vacuum during two consecutive intake strokes on Cylinders 1&2, but not during the next two consecutive intake strokes on Cylinders 4&3. The same principle would hold true using TB's 2&4, 1&3 or 3&4.
However, using the vacuum ports from TB's 2&3 will provide vacuum during alternating intake strokes... Cylinder 1 (none), Cylinder 2 (vacuum), Cylinder 4 (none), Cylinder 3 (vacuum). The same would hold true using TB's 1&3.
Compared to using vacuum from any one TB, I'd guess the first scenario would provide a stronger vacuum but the second secnario would provide a smoother vacuum response which could effect which TB's you would want to use in a given situation.
Vacuum at any given cylinder is only created during the intake stroke, or once every 4-strokes, which explains the wild fluctuation after connecting the vacuum tester to just one TB.... one stroke with vacuum followed by three strokes without vacuum. Using all four throttle bodies smoothed out the response since there was always one cylinder providing vacuum.
Apparently using vacuum ports from any two TB's won't necessarily give the same results... for example, pairing TB's 1&2 can have a different effect than pairing TB's 2&3. I'm sure someone else can explain this better than me... and feel free to do so...
During one intake cycle, using the vacuum ports from TB's 1&2 will provide vacuum during two consecutive intake strokes on Cylinders 1&2, but not during the next two consecutive intake strokes on Cylinders 4&3. The same principle would hold true using TB's 2&4, 1&3 or 3&4.
However, using the vacuum ports from TB's 2&3 will provide vacuum during alternating intake strokes... Cylinder 1 (none), Cylinder 2 (vacuum), Cylinder 4 (none), Cylinder 3 (vacuum). The same would hold true using TB's 1&3.
Compared to using vacuum from any one TB, I'd guess the first scenario would provide a stronger vacuum but the second secnario would provide a smoother vacuum response which could effect which TB's you would want to use in a given situation.
