Vacuum Gauge, My Observations
 

So on my swift I have recently installed a 14.99 Princess auto vacume gauge. It is not mounted yet and sits in one of my cup holders.

At idle it reads at 25Hg and it moves very quick with throttle input.

While driving I noticed that alot of my typical acceleration would have the guage reading 0Hg. I tryed different throttle inputs and found I can climb most hills without going below 5Hg. There are a few that need WOT in gear and 0Hg. In typical coast driving, I.E. level ground to a slight uphill grade I find I can keep it at 10-15Hg.

Has anyone else noticed how sensitive to throttle input the gauges are. I have found that I can move the needle with such imperceptable throttle changes. I can now bring the vehicle to accelerate by bringing the gauge to 5Hg instead of my usual response which would be a 0Hg.

Another thing I noticed was when the vehicle begins to build vacume on a slight downhill I can find at 20Hg I can push in the clutch and begin a coast.

Anyway if I make any other observations I'll share them. Have you noticed how your cars react?

I have a vacuum gauge on my '88 Escort. You are correct about how little you have to change the throddle opening to make a huge difference in engine vacuum. Mine reads 20-21 In/Hg at idle and on flat road which there's not much of around where I live I can keep it at 15-18 In/Hg. On smaller hills I'll usually drop to 10-15 In/Hg, on larger hills I'll drop down to 3-10 In/Hg and about 25 In/Hg during deceleration. Lots of people say they get better mileage accelerating down a hill to get momentum for the upcoming hill, but I've tried it in my car and I always do better coasting down the hill and start accelerating right at the foot of the hill before I lose any speed and momentum.

I notice that exact same thing

Now I had a chance to see what drafting is all about the other day. Well yesterday. I was in the slow lane driving and a dump truck passed me but realized he would be losing speed for the upcoming hill and changed lanes in front of me. Well I was reading 10Hg on the flat part of the road and when he pulled in front of me, say 5 car lengths, the vacuum began to rise and sat at 15 Hg with the truck in front of me. I figured he was too far ahead to obtain a measurable difference from his wake but I did, so I moved a bit closer after the hill, which needed less throttle then usual with him in front of me, and the vacuum read 15-18Hg. His exit was approaching and he merged off the road and my vacuum then dropped to 10-12Hg almost imediatly after he merged and I had to tip the throttle a bit to maintain my speed, approx 85km/h.

Just another observation

I've not tried drafting trucks in a long time, but I have also noticed that when one gets in front of me my engine vacuum will increase several In/Hg at distances up to 200-300 feet. Next time I go on a road trip I may see if I can find a truck that isn't driving but 60-65 mph and draft him at a couple hundred feet which is about 10-12 car lengths. That should be a good safety cushion.