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Vacuum Tank Performance at High Altitude


jrbartlett

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Does anyone have experience running a vacuum-tank-equipped car at high altitude (Rocky Mountains west of Denver)?

I am thinking about taking my '29 Packard on the Glidden Tour, but have never driven it in the mountains and am concerned about whether the vacuum tank is up to the job, considering the long climbs and reduce atmospheric pressure (since it is this pressure that pushes the fuel from the tank).

Any comments?

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Guest Trunk Rack

You would be smart to educate yourself on fuel volitality, known technically as RIED VAPOR PRESSURE.

Here's the problem. In earlier days, the vapor pressure of fuel was much lower than today. That is why you saw devices like the "Fuelizer" on cars as late as the early 1920's. It was little more than an extra spark-plug in the intake manifold, to give the gasoline an extra "kick" so it might "light off" in the combustion chamber.

Obviously, the higher the fuel vapor pressure, the easier it is to get a car started on cold mornings. Thus, depending on the time of year, refiners alter the vapor pressure.

The important thing to remember, is that if you SUCK fuel thru a gas line, you effectively RAISE its vapor pressure, making it more likely to vapor lock. All cars built in the last few years have fuel injection systems, with powerful fuel pumps typically located INSIDE THE GAS TANK. Thus ALL fuel is under positive pressure, so it can not vapor lock regardless of heat or altitude.

Depending on the time of year and location of where the gasoline you happen to buy on any given day, you may or may not experience vapor-lock in a system that was designed for 1920's era fuels.

My recommendation is to do what most everyone else who dosnt want to worry about vapor lock in an otherwise perfectly maintained old car does - INSTALL AN ELECTRIC FUEL PUMP. Mount it as LOW as possible as CLOSE the the BOTTOM of the gasoline tank as possible. Then the fuel to the carb. will be under PRESSURE, and you can forget about vapor lock.

The typical six volt fuel pumps that are commercially avail. have a upper limit on fuel pressure of about 3 lbs. That will NOT force open your carb's "needle/float valve. However, if you are worried about leakage thru that valve, with a little "hunting" you can come up with a modern float valve that will eliminate any question of sealing.

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Thanks Pete, but I already know this, which is why I posed the question.

Actually, my vacuum tank has been working quite well at sustained 55 MPH speeds in hot weather here in Texas. But I recognize that it's a whole different ballgame at the prolonged wider throttle openings on those long mountain climbs.

My option is to take a different car that already has an electric pump installed.

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Some years back some antique Chevy owners took their pre 30's up Pikes Peak. These were 4 cylinder cars equipped with vacuum tanks. The story they tell is that the only problem they ran into was not having sufficient vacuum to keep the tank filled so once every few miles they would have to let off the gas pedal, allowing an increase in vacuum, for just a second or two, and they would continue on their way.

Just like vacuum wipers with the throttle wide open or going up hill a vacuum tank will quit drawing fuel while under load.

I know of one man who has an electric fuel pump in addition to his vacuum tank. On those rare occassions his vacuum tank runs out of fuel going up hill he has a toggle switch to turn on the electric fuel pump for a few seconds filling the vacuum tank.

I have yet to have problems with mine but then I have never been on any "real" hills with it. Give me time. wink.gif

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Chris Coon</div><div class="ubbcode-body">The electric fuel pump in line on a seperate toggle switch works very well, just don't leave it on to long or it will overflow the vaccum tank. The pump causes no restriction in the line when turned off. </div></div>

That's exactly what I've been told

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Chris Coon</div><div class="ubbcode-body">The electric fuel pump in line on a seperate toggle switch works very well, just don't leave it on to long or it will overflow the vaccum tank. The pump causes no restriction in the line when turned off.</div></div> That's how I run one of my '31s.

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A Little Humor Here.....

Met this fellow in Lebanon, TN at the meet there this past weekend. I walked up and observed his middle 20's car(don't want to identify him). I saw that his vacuum tank had a fitting at the bottom of the tank without an attached fuel line. I asked him if he had an electric fuel pump?

"No!" He replied!

I looked at him with a questioning glance?????

(Please note that I had my 2009 Philly name tag around my neck, which may have looked "official" to him.) cool.gif

"Are you an AACA judge?", he asked.

<span style="text-decoration: underline"><span style="font-weight: bold">"No </span></span>!",I replied. "Not this class!"

(I actually didn't judge at all, worked the membership booth.)

"Well then, yes!", He replied. "I thought I had it well hidden." grin.gif

We had a wonderful conversation about his early car and its operation. It was just so funny to hear him change direction on his story so quickly, though.

Wayne

post-31395-143138085307_thumb.jpg

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  • 2 weeks later...

Can't give any help on the vacuum tank but I can tell you pay attention to your brake fluid. Dad toured his 29 Franklin limo to the top of Pikes Peak. After an

un-eventful ride up it was time to descend. It was at that time Dad realized he had no brakes. It seems that the silicone brake fluid everyone had become in love with, had changed into something that would not function in an old vehicle at that elevation.

The Franklin was nursed down the "hill" on a tow strap hooked to a good ole' GM Suburban. It could have been a disaster had the braking issue not been found at the top.

Be careful.

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