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Discussion Starter · #1 ·
I am going to put a permanently mounted vacuum gauge on the steering column in my '26 T. Looking at the available gauges I came across electrical vacuum gauges on Summit's website. I didn't even know there was such a thing. It would be easier to install than a mechanical gauge. I am wondering about the performance of the gauge? Also I am wondering what the sending unit looks like and how it connects to the vacuum line? Does anyone have any experience with electrical vacuum gauges?
 

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If you don’t mind excess modernism in your T, then a digital is the easiest to read at a glance.

For analog read outs I like mechanical but in reality my projects mix it up with electrics, for myself I usually avoid digital gauges except on actual racing vehicles because at least those with simple numeric read outs they are easy to read with just a glance while everything including you are shaking in heavy vibration and impacts.

Bogie
 

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Discussion Starter · #6 ·
I like analog gauges. In my opinion they are easier to read than a fast moving digital gauge. You do need to know your gauge to read at a glance though.
I always had mechanical vacuum gauges. I just had never heard of an electrical vac gauge.
 

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Discussion Starter · #8 ·
In the racecar I would orient the gauge so the needle was straight up during normal operating conditions. Except the tach. I never looked at that while racing!
 

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If you don’t mind excess modernism in your T, then a digital is the easiest to read at a glance
I disagree. The absolute number is irrelevant on most gauges. What matters is trending - is the temp climbing, is the oil pressure dropping, etc? Analog gauges are much easier to keep track of trends. As noted, real racers mount the gauge so that the needle is straight up at normal operating conditions. This makes it extremely easy to assimilate the data at a glance. Digital readouts require much more attention and mental processing to glean the useful data. And frankly, you're measuring an analog signal (pressure). One aspect of my day job is understanding and evaluating telemetry data from aerospace systems. Digitizing analog data always compromises fidelity.
 

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Just out of curiosity why a vacuum gauge to read while driving? I can see it as a useful tool setting up the carburetor and tuning. It‘s not like a tach, temperature, or oil pressure that is an “alarm” if out of range.
 

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So the thing that's really going to matter is how the gauge operates.
You're saying it's an "electrical" gauge, but some people are referring to "digital".

So we need to discern between "electro-mechanical" vs. "digital".
Some electrical gauges use the "bi-metal" thermal operation, which takes time to move the gauge.
They're only good for things where the gauge only needs to change gradually (fuel, temp).

For anything that changes quickly, mechanical is much better.
If the digital sending unit and gauge show instant results (I'm assuming they should), then that should work just as well.

Example:
I had bought an electrical trans pressure gauge, and never gave any thought to how it would operate.
Once I installed it, I realized that it couldn't give me a readout of the trans pressure as it varies with the throttle.
So I had to get a mechanical gauge for that.
The electrical would've been fine for a tow vehicle, just to make sure you have good pressure as you're cruising down the highway.
But to be able to monitor instant pressure changes as the throttle varies, it had to be mechanical, although I'd assume digital could also give you instant results.
 

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That's the problem with digital readouts , they process & display too quickly , by the time we see it & attempt to process the information , its changed !!
That's a good point... if you are considering digital for something that changes rapidly, you'd be best off with a digital "sweep" readout, rather than numbers.
That way you're simulating a mechanical dial gauge.
Otherwise, you're better off with mechanical.

My $0.02 is that for vacuum I'd just go with a standard mechanical gauge, since you're just running a vacuum line to the gauge.
With gauges that require fluid connections, I can see why you'd want to have an electrical gauge if feasible, so that you can avoid the chance of fluid leaks inside the vehicle.
But for vacuum, there isn't much difference between running a wire for an electrical gauge, and running a vacuum line.
 

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Discussion Starter · #16 ·
Just out of curiosity why a vacuum gauge to read while driving? I can see it as a useful tool setting up the carburetor and tuning. It‘s not like a tach, temperature, or oil pressure that is an “alarm” if out of range.
I'm still into the distributor thing on my Model T. I want the vacuum gauge to get a better understanding of how timing is affected by the vacuum advance. When and how much vs load. I could temporary my gauge in, but it might as well be a nice permanent installation. My experience is with race motors. Never used vacuum advance. Rarely even used mechanical advance. 34 degrees locked. :) Any way, I like gauges. The more the better!
EDIT: It might even help my lead foot get better gas mileage.
 

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I'm still into the distributor thing on my Model T. I want the vacuum gauge to get a better understanding of how timing is affected by the vacuum advance. When and how much vs load. I could temporary my gauge in, but it might as well be a nice permanent installation. My experience is with race motors. Never used vacuum advance. Rarely even used mechanical advance. 34 degrees locked. :) Any way, I like gauges. The more the better!
EDIT: It might even help my lead foot get better gas mileage.
I run them in my hot rods for the same reason. I usually fitted my distributors with adjustable vacuum advance canisters. After driving the car for awhile and observing the way the vacuum responds to load, I could dial in the advance to decrease rapidly as load and throttle opening went up. That way I could optimize advance for both cruise and power. These were all street engines of course. Tuning the advance was done with a hand held vacuum pump while watching how the timing responded.

I like mechanical vacuum gauges because mech gauges usually have a greater sweep making them easier to read. Somewhere around 270*, however, Speed Hut makes an electric vacuum gauge with a stepper motor drive that gives about the same sweep.
 

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Even if your model T has a flat head 4 banger the manifold vacuum measured with a mechanical gauge is going to give instant reading to any change to throttle and/or advance. I would think any mechanical to current conversion would be as it was a bit a go.
Any reading ported would be abstract as far as information as to what your doing that is affecting efficiency. What ever way you go report back the effectiveness.
 

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Discussion Starter · #19 ·
That's a good point... if you are considering digital for something that changes rapidly, you'd be best off with a digital "sweep" readout, rather than numbers.
That way you're simulating a mechanical dial gauge.
Otherwise, you're better off with mechanical.

My $0.02 is that for vacuum I'd just go with a standard mechanical gauge, since you're just running a vacuum line to the gauge.
With gauges that require fluid connections, I can see why you'd want to have an electrical gauge if feasible, so that you can avoid the chance of fluid leaks inside the vehicle.
But for vacuum, there isn't much difference between running a wire for an electrical gauge, and running a vacuum line.
Really the only reason I am considering an electrical gauge is that I can run a wire through the firewall in an existing grommeted hole for wires, but would have to drill a new hole and grommet it for the bigger vacuum line and the wire could come up the steering column with the turn signal and horn wires. IMHO a cleaner and easier install.
 

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Discussion Starter · #20 ·
I run them in my hot rods for the same reason. I usually fitted my distributors with adjustable vacuum advance canisters. After driving the car for awhile and observing the way the vacuum responds to load, I could dial in the advance to decrease rapidly as load and throttle opening went up. That way I could optimize advance for both cruise and power. These were all street engines of course. Tuning the advance was done with a hand held vacuum pump while watching how the timing responded.

I like mechanical vacuum gauges because mech gauges usually have a greater sweep making them easier to read. Somewhere around 270*, however, Speed Hut makes an electric vacuum gauge with a stepper motor drive that gives about the same sweep.
Yeah, that's what I figured. I could get a better understanding with my vacuum pump and timing light.
That gauge from Summit I referenced has a 270 degree sweep.
 
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