Vacuum gauge and throttling loss (vehicles, fuel, tire, best)

[nick gar]

Car has an an efficiency meter which is nothing more than a vacuum gauge. I like to not live by "what my grandfather told me." I know cylinders drawing air through a closed throttle is a source of efficiency loss called throttling loss.

There is a sweet point where throttle plate losses are minimal while the air-fuel ratio remains lean (full throttle= no throttle loss but very rich AF ratio).

Any tips to put this feedback sensor to use?

Ps my similar era Bimmer at least tapped the FI circuitry, even though the gauge was a confusing logarithmic scale and by 2008, worked only with a serous rap on the dashboard.

[ukrkoz]

serous rap? I know serous membranes...

Anyhow. Here's wild one for you. Called E-Ram.

[GregW]

Engines are most efficient at WOT at peak torque. You can rarely drive there however so the lowest RPM that can carry the load is most efficient.

[arleigh]

I don't understand , are you trying to find another use for it ?
Or are you trying to get better gas milage ?
One thing I have learned relative to that situation is modifying a significantly larger air filter .
All air filters act as a choke , especially at higher speeds, it's constant never changes with the change in RPM .
The only way to compensate for that is an oversize element .
I lived in the mountains 7K feet elevation you loose 20% of our horse power (lack of air)
I worked on boats as well ,and it was a serious sciense when some one wanted a turbo on a boat engine , in the end it didn't work out when the custmer took the boat down to sea level ,bad things happen . (to many pieces).
Because boats starve for air to begin with they do not have any paper element , only a flash screen over the intake for safety.
Eliminate the choke and maximize your effeciency .= over size element .
Some of my friends do this to their vehicles before they even leave the car lot for the first time, SOP.
On you meter , It is likely the gears leavered from the bordon tube lack lubrication,and that will always be a problem sticking . Usually they are made of brass but as time and wear take their tole especially if there is a lot of action in a very small area of the gear pattern,pinion to rack ,the brass simply breaks down .
I worked on air compressors a long time and played with pressure and vacuum gages a lot . when it's your world, you want to explore it all.

[nick gar]

Economy

[M3 Mitch]

Is that a Mercedes? Make, model and year would help figure out your question.

If the car has FI rather than a carb, I would doubt it's really a vacuum gauge, but rather something like what your BMW had - a read out that looks at road speed and fuel flow (injector open interval or %)

Typically one gets about the best economy that can be had short of "hypermiler" techniques by short-shifting a manual trans, opening the throttle a bit more and shifting up at a bit less RPM than "typical". Important not to over-do this though. With an automatic you are stuck with the shift points designed into it, although sometimes by lifting the throttle a bit when you know from experience it's about ready to shift up will "encourage" it to go on and shift a bit sooner.

[nick gar]

Servicing vacuum gauge

[nick gar]

I think I now understand what a vacuum gauge is used for. Skipping grandfather's advice, my father used a vacuum gauge on his boat to indicate load on the engine. Propeller pitch, engine RPM and hull planing velocity are wildly varied between vessels, yet fixed to a particular boat. Efficiency can be inferred from matching vacuum gauge readings with logs containing speed, distance, and fuel consumption.

I normally do all around town driving and was trying to use the gauge to maximize efficiency knowing it lays between a full jackrabbit start, and a slow take-off (the latter if I obeyed the gauge). Having burned through a tank with jackrabbit starts, I'm at 15.8mpg, opposed to 16.5 mpg babying the car after I first bought it.

I now will use the manifold vacuum as a good indicator of load while cruising on a highway, and nowhere else. A headwind, a mild grade, or low tire pressure are just a few of the indicators my Economy gauge will swing past rest position while cruising 60mph.

[nick gar]

Originally Posted by M3 Mitch

Is that a Mercedes?
sometimes by lifting the throttle a bit when you know from experience it's about ready to shift up will "encourage" it to go on and shift a bit sooner.

Yup, '89 MB S-Class, 6cyl gasser. The last month I've kinda skipped 3rd gear, does that count? Car is programed to start in 2nd, so I roll in the throttle as to not cause a brief drop into first, yet stop at WOT which is a high enough RPM the transmission chooses 4th gear.