Carbuerators and high elevation.

[Coupe Deville]

Hello everyone, This may be considered a "technical" question, so if this is in the wrong section feel free to move it. But I feel like some people in the club who live in high altitude areas deal with this everyday so it would fit in the "general discussion" section.

I have a 1972 Cadillac Coupe Deville, with the original 472 engine and HEI. The carburetor was professionally rebuilt 4 years ago and has no problems whatsoever. It is the original 4BBL quadrajet that came on the car from the factory. Original jets, rods, everything. Only thing that is changed on it is that the idle mixture screws are very much on the lean side, of normal tune. What altitude does a 4BBL (or any carbureted V8 car of that matter) start to have serious trouble climbing hills in high elevation? Reason I ask is, on I-40 in Arizona, the elevation will get as high as about 7,300 feet. Will my Coupe Deville have trouble keeping up in that altitude? Ive driven in high elevation before, but never in a carbureted car. Is the problem of the engine starving for oxygen and being out of tune as bad as people really say it is?  I would really appreciated some input on this one. As always, thank you!

-Gavin

[Carl Fielding]

Gavin , IMO general is the best place for this general interest guestion : sooner or later , the lucky cruisers among us will find ourselves at altitude. As a long distance driver with considerable experience over 10,000 feet , up to 16,000+  in South America , the most important factor is octane. If I were to be spending any length of time on high , I would lean it . If just a quick trip over a pass , I would not bother. Southern gas was quite good. I seem to remember something like 98 octane for coastal driving 40 years ago. High altitude octane was 70 something. Pulling grades was where you had better have had low octane . I have been in situations where a u-turn would have been your only option if you neglected octane management. I am fanatic about this. I climbed White Pass in Cal in my '79 Ford Van. 460 mill , I think that was about 11,000'. I think the lowest octane I could find was 87. I just can't remember if the 85 octane gas you find in Rocky Mountain states was available . That Ford did great. Also , if you will tune for prolonged duration at altitude , you can advance the timing a bit. The good news is that these 472/500 Caddys , even the low compression '71 and newer really do just fine running the lowest octane gasoline available. And remember , you drop I.Q. at significant elevation. I had just come up to 15,000' in the Andes from sea level in my new '77 Blazer. Put it on its side out of sheer stupidity. Took 12 guys working pick and shovel all day , and a beautifully rigged winch operation to get back up. Ask me about it next time we are kicking it around the campfire.  - CC

[David Greenburg]

When I lived at altitude (6000 ft)with an old car, I set my timing with a vacuum gauge; maximum vacuum and then back off 1". Set like this the car ran great, and easily handled excursions up into the mountains (8-9000 ft.)

["Cadillac Kid" Greg Surfas 15364]

Gavin,
Higher altitude means less Oxygen (per cubic foot of air) which means less available to burn gasoline which means the car will run rich and loose power.  There is an "altitude" carb that is jetted leaner, so if your intentions are to run at high altitudes continuously I would suggest re jetting (and rods too) to the "Altitude" carb specs.  Otherwise, your motor will have plenty of power for normal operations.  The only thing I noticed with my '72 Eldo at 6500 feet was a loss of some power.
Greg Surfas

[The Tassie Devil(le)]

As an aside, in 2002 when  touring USA, I was driving from Sacramento to Lake Tahoe.   

During the drive, I commented to my wife that there was something wrong with the car, and I was a bit concerned as we still had another 3 months and 14,000 miles to go.   The car was losing power at an alarming rate, even for a V6.   

Rounding a corner, I noticed the sign on the side of the road giving the height above sea level at something like 7,000 feet.   I knew immediately what the problem was, and upon driving back to Sacramento, later that day, I noticed the remarkable increase in power as we descended the mountain.

Never came across the phenomenon before as mountains in Tasmania only get to 4,600 feet.   That is those that we can drive up.

Bruce.

[David Greenburg]

4,000 ft.?  That is a "hill."  Try driving to the top of Pikes Peak in Colorado (14,000 ft. plus).  Even in a modern, fuel injected car, you and your car will both notice the lack of oxygen, especially after you pass 11,500-12,000 feet. Some folks fly from sea level to Colorado, jump in their rental cars and drive up to the top of the Peak.  When they get out of their cars at the visitor's center, you can tell who they are, because they look/act like zombies.

[The Tassie Devil(le)]

I know about Pikes Peak.

Went up there in 2008, with John Washburn at the wheel of his own vehicle whilst my wife and I enjoyed the scenery, and took lots of pictures.

At the top, I had trouble moving around, and when I got back to the car for a rest, there was John, stuck into his Oxygen.   Actually, plumbed into his oxygen supply.

Bruce.

PS.   He did stop part way up so we could "acclimatise" to the altitude.   He is a nice fellow.

[Carl Fielding]

Test , test , test. I just had one of my insightful thorough compositions wiped out. I will try to re-post under more robust conditions.  - Carl

[Carl Fielding]

The altitude at which any engine develops problems climbing hills depends on grade. You will have no trouble on an Interstate at 7300'.  - CC

[raugusti]

As another high altitude dweller (7500ft) north of Colorado Springs, I don't think you will have any problems that warrant making changes just passing through.   Living here I lean out the carb and retard the timing to compensate for the lack of oxygen.

Scott 

[bcroe]

I've been up Pikes Peak 3 times, all using a carb. It doesn't run great at
the top, but it ran.  I suppose a V6 might have problems with power; I
had plenty of cubic inches.  I never noticed an issue at 7000'.  Bruce Roe

[Walter Youshock]

My sister drove us there in her Honda CRV years ago.  I remember it would run ok on the east side of the mountain and we practically had to push it when we were on the West side.

I also remember GM was testing Pontiacs when we were there.  They were on the way down the mountain as we were climbing.

And the altitude definitely affected me.  Even at her house which was at about 10000 feet, I had trouble getting around.  I'll take sea level, thank you...

[bcroe]

My sister drove us there in her Honda CRV years ago.  I remember it would run ok on the east side of the mountain and we practically had to push it when we were on the West side.

I also remember GM was testing Pontiacs when we were there.  They were on the way down the mountain as we were climbing.

And the altitude definitely affected me.  Even at her house which was at about 10000 feet, I had trouble getting around.  I'll take sea level, thank you... 

A couple years ago we had our 2001 CRV up to 11,000' at Alma, CO.  That
fuel injected 4 banger with 5 speed stick had no problems, but I certainly
had limited energy up there.  Gives us flat landers a headache.  Bruce Roe

[John Washburn CLC 1067 Sadly deceased.]

You lower elevation folks are fun...

Besides taking Bruce to the top of Pikes Peak in my wife's 92 GMC the 37 LaSalle, the 49, 53, and soon to be back on the road 56 run ok when you adjust and re-jet them for altitude.

But if your are just touring the loss of power is to be expected, as was the case with all carburetor cars, so just enjoy the drive stay in the slow lane and all will be well.

6,000 foot Johnny