Curtis - thanks for the reply. Makes sense, but it doesn't really feel like the engine is stalling due the brakes being applied, but rather due to the vacuum line being "plugged up" when the line collapses.

I have not changed the master cylinder yet, but was planning on ordering one. Do you suggest sticking with the 240 one or going with the 280 version?

Curtis - thanks for the reply. Makes sense, but it doesn't really feel like the engine is stalling due the brakes being applied, but rather due to the vacuum line being "plugged up" when the line collapses.

I have not changed the master cylinder yet, but was planning on ordering one. Do you suggest sticking with the 240 one or going with the 280 version?

Thing is, the vacuum line feeding the Master Vac is dedicated to the Master Vac, so whether you connect the vacuum line to the Master Vac or not has no effect on the engine performance. It does however effect how well your brakes work. You can test this theory by capping off the vacuum line to the Master Vac and your engine will run fine, but BEWARE your brakes will be very hard to push and the stopping distance will be compromised!

The 280ZX master cylinder is 1/16" bigger in diameter so it moves more fluid for the same amount of pedal travel. If you also changed to a larger front caliper, then your pedal travel is probably too long compared to OEM. So in that case if you want to shorten your pedal travel, the 280ZX master cylinder would address that. Note that the 280ZX master cylinder has the front and rear reservoirs switched as compared to a 240Z so you will have to swap the brake lines accordingly.