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Old 08-28-2015, 10:36 AM   #11 (permalink)
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Originally Posted by Fat Charlie View Post
It follows that "being in a hurry" is more about living the stress than actually getting somewhere more quickly. I can't help them get there sooner, all I can do be amused at their stupid and unconstructive reactions to unnecessary stress.
I agree about it being so much less stressful when driving on the far right, freeway lane at 55-60mph.

Before "seeing the light" of moderate freeway speeds, I can recall how stupid I felt speeding to my destination, parking, then to dally around my car, and then see the car that I rushed past on the freeway pull into the same parking lot.

I treat metropolitan freeway driving as if I'm in a controlled air traffic control space. 747s don't maintain their cruising speeds when beginning their landing patterns in a crowded air space. The ATC slows them down so they play nice with the other air traffic.

The Zen of driving slower comes from how you mentally frame it.

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Old 08-28-2015, 10:40 AM   #12 (permalink)
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Originally Posted by RunningOnEmpty View Post
...you'll probably find that driving economically will not make you popular with commuters that are in a hurry.
Originally Posted by Fat Charlie View Post
To hell with their popularity: embracing the suck doesn't mean doing everything you can to make it suck more.
....I can't help them get there sooner, all I can do be amused at their stupid and unconstructive reactions to unnecessary stress.
like it.
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Old 08-29-2015, 09:54 AM   #13 (permalink)
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Originally Posted by RunningOnEmpty View Post
Doug, you appear to have made a faulty assumption about gas consumption being linear to throttle position.

Get a vacuum gauge and mount it where you can see it without being distracted from driving. It will have a single port on the back and you will want to run an 1/8" vacuum line (vacuum line has a heavy wall so it doesn't collapse) to the intake manifold and tee off an existing vacuum port. You'll want to find one that is down stream of the throttle blades.

When you drive, try to keep the needle as high as possible. It will be quite a challenge but will lead you to more economically driving techniques.

The gauge will pay for itself but you'll probably find that driving economically will not make you popular with commuters that are in a hurry.
The idea is to operate the engine at the most efficient load (and speed)possible. The efficiency falls, after peaking, at the very highest manifold pressures/loads.

You don't want manifold pressure as high as possible, rather as high as possible before getting into fuel enrichment (simplistically) and falling over the other side of the efficiency peak. How deep into the throttle this is depends on engine speed. You really need two "gauges"; one for manifold pressure (MAP) or throttle position, and some indication of O2 sensor feedback.

Throttle position tracks with MAP up to the point where the engine is consuming the maximum amount of air it can at a particular speed. (I have observed this on data logs.)

After that point, opening the throttle further will not affect airflow (and so fuel consumption). This will be past the point of entering into fuel enrichment and maximum efficiency. With O2 sensor information you can use throttle position or MAP to determine the most efficient operating load.

Assuming a narrow band sensor, the same circuit from the link ^ without the 330 Ohm resistor will read - 0-1V - O2 sensor voltage. An alternatively is a comparator based circuit described in an Autospeed article - and linked to in other threads on here.

If an indication of MAP is preferred, an '89 Honda Civic has (although it may depend on which market it was sold in) a MAP sensor with a 0-5V output. The circuit ^ will work using the output from that.

For a car that does not come OEM with a MAP sensor (eg. Miata), they are inexpensive to buy used (careful; some types don't output 0-5V) and a regulated 5V is easy to set up from battery voltage. It is good practice to use a 16V Zener on the battery voltage side and capacitors to ground on either side of the 5V regulator.

An alternative to a stand alone 5V supply is to tap into the regulated 5V sensor supply on the car. Watch how much extra current - proportionally - is being drawn by what you are adding on though. The 1M Ohm resistor serves to limit the current in the ^ circuit.

If a numerical indication of either MAP or throttle position is preferred the 0-5V output can be scaled with a voltage divider and fed into a 0-200mV digital panel meter. eg. 5V (nominal voltage at atmospheric pressure) can be divided by 50 to read 100mV (~kPa) or by 34 to read 14(.)7mV (~psi).

Driving efficiently (pulse and glide) involves what most people would agree is brisk acceleration and then coasting. Slow deceleration, as might occur when travelling towards a red light, can be confused with driving slowly.

The most efficient engine speed range is likely to be in the realm of 2-3000 rpm.

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