m-mman

Vacuum accessories and their affect on motor operation

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I just got a 1946 Automotive News newspaper and in it is an advertisement from the Trico corporation for their line of vacuum powered windshield fans.  (the little ones that mount on the steering column or dashboard)  

 

The ad text reads:

"Here is one fan which puts no drain on your battery - which requires no wiring - which operates on cost free harnessed air power and as dependability as your windshield wiper."  The target audience would likely also include heavy trucks. 

How truthful do you think this position is? 

 

Is the operation of a continuous vacuum accessory (fan/wiper) actually 'cost free'?   (fuel and maintenance)

An electrical drain would require a little more effort to spin the generator, but these things are essentially functioning as a vacuum leak.

 

Is the engine perhaps operating a little leaner because of them?

The additional air is brought into the manifold after the carburetor, but how many CFM of non-fuel air would it possibly be?

Would a leaner mixture somehow result in better MPG?

In mileage contests all non essential electrical drains are stopped, but nobody induces a vacuum leak for better fuel mileage. 

 

Maintenance - An electrical drain might wear the brushes faster, but could a 'vacuum leak' burn the valves faster? (or do any other damage?)

Maybe these slight differences would show up only in the cost conscious area of commercial trucking. 

 

With a 3 brush generator system, tuning the electrical output to compensate for various electrical accessories might be difficult, so before regulators, perhaps vacuum power was better?

 

An engine's vacuum 'draw' (inches of Hg) I think is consistent regardless of the size, number of cylinders or design (OHV, side valve) Is this true?

As engines evolved from say 1920 to 1940 were there changes in their ability to operate a continuous vacuum accessory? (Not talking about vacuum drop when climbing a hill, but a lower power engine would certainly have the throttle open farther and therefore provide less vacuum)

 

Do you think Trico's claims were accurate? or were they promoting a dying technology? Continuously operated vacuum powered accessories. . . . 

 

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Posted (edited)

It only takes a tiny (REALLY tiny) vacuum leak to screw up fuel distribution. However, in the 30s a lot of cars were jetted (for various reasons) way too rich. I guess you could get away with it. Meanwhile, the quite a few of electrical systems of the day weren't really good enough to carry much in the way of accessories. Maybe it made sense.

 

You usually see vacuum taps (for wipers or whatever) way at one end of the manifold. That sounds like the worst possible place to me. Anything that is known to leak should be leaking where it will mix with the incoming air/fuel, probably right under the idle jet.

 

 

 

 

Edited by Bloo (see edit history)

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1 hour ago, m-mman said:

I just got a 1946 Automotive News newspaper and in it is an advertisement from the Trico corporation for their line of vacuum powered windshield fans.  (the little ones that mount on the steering column or dashboard)  

 

The ad text reads:

"Here is one fan which puts no drain on your battery - which requires no wiring - which operates on cost free harnessed air power and as dependability as your windshield wiper."  The target audience would likely also include heavy trucks. 

How truthful do you think this position is? 

 

Is the operation of a continuous vacuum accessory (fan/wiper) actually 'cost free'?   (fuel and maintenance)

An electrical drain would require a little more effort to spin the generator, but these things are essentially functioning as a vacuum leak.

 

Is the engine perhaps operating a little leaner because of them?

The additional air is brought into the manifold after the carburetor, but how many CFM of non-fuel air would it possibly be?

Would a leaner mixture somehow result in better MPG?

In mileage contests all non essential electrical drains are stopped, but nobody induces a vacuum leak for better fuel mileage. 

 

Maintenance - An electrical drain might wear the brushes faster, but could a 'vacuum leak' burn the valves faster? (or do any other damage?)

Maybe these slight differences would show up only in the cost conscious area of commercial trucking. 

 

With a 3 brush generator system, tuning the electrical output to compensate for various electrical accessories might be difficult, so before regulators, perhaps vacuum power was better?

 

An engine's vacuum 'draw' (inches of Hg) I think is consistent regardless of the size, number of cylinders or design (OHV, side valve) Is this true?

As engines evolved from say 1920 to 1940 were there changes in their ability to operate a continuous vacuum accessory? (Not talking about vacuum drop when climbing a hill, but a lower power engine would certainly have the throttle open farther and therefore provide less vacuum)

 

Do you think Trico's claims were accurate? or were they promoting a dying technology? Continuously operated vacuum powered accessories. . . . 

 

 

Wow you have been busy thinking; my take is that, as mentioned, back in the day electrical accessories were troublesome and vacuum was potentially less so.

 

As to burning valves, leaning mixtures etc. I would think the volume of manifold air extracted wouldnt  be significant enough to cause any grief, after all how many vehicles with vacuum wipers, vacuum fuel pumps etc. do you think suffered from these issues.

 

Time to turn out the light and start counting sheep 😉

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Posted (edited)

Think in volume.  I've never used one of the vacuum fans to test, but I have rebuilt and tested, many SW vacuum tanks and Trico wipers.  Compared to the volume of air an engine is pulling in, a wiper motor's  air leak is tiny and doesn't affect engine. You can see that with a tachometer, or vacuum gauge hooked up to the motor. If all is working as it should, the RPM's don't change because there isn't enough change in the air/fuel ratio.

 

A properly operating vacuum tank will pull more volume (leak air) than a wiper motor and as such, slightly drop the rpm's at idle as it cycles on. Still not enough to stall the engine and at higher RPMs there the engine is pulling even more volume so that the proportion of the vacuum tank's air leak is even less.  

 

And, keep in mind that a vacuum tank is not pulling just air, there are gasoline fumes mixed with that air from the vac tank, also. So it doesn't get lean enough to harm the motor.  If it did, there'd have been so many damaged motors that the industry would not have used vacuum tanks for over a decade until mechanical fuel pumps started to be used in the late 1920's.

 

Paul 

Edited by PFitz (see edit history)

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This is a video of the vacuum tank operating on my 29 Cad. 

When the tank is full there is no vacuum loss. Then as the level gets low it draws vacuum for a few seconds and shuts off again. So, not a continuous leak. And yes the vapors in this system might not represent a pure atmospheric type leak.

 

A vacuum powered HVAC part or a vacuum advance would also operate for a few seconds then there would no longer be a vacuum leak.

The fan & wiper system however would provide a continuous leak. . . . . 

 

Perhaps with the crude carbs of the vacuum wiper era (running rich?) and the fact that the device(s) would be operated mostly at highway speed, the loss might be insensible.  But a long drive with both the wipers going AND the fan spinning there must have been a leaner mixture. 

The vacuum leak from the wipers while operating is probably less than from a broken or disconnected vacuum wiper rubber line. That situation I have noticed on an old car. 

 

If you operate the lights, electric heater fan and every other electrical accessory and have a weak battery, it is possible to overdraw the generator output and possibly stall the engine. (idle)

If you operated every possible vacuum accessory (top? antenna? etc.) perhaps you could also stall the engine at idle? Hummmmm. . . . 

Maybe I will just go back to sleep 

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