Too bad high altitude and four wheeling don't match quite as well. Here are some tips to help you and your rig work better in the high country. Many of you have seen the documentaries on climbing the high peaks, such as Mount Everest in Nepal, where dealing with the effects of altitude is a life or death situation. Well, going over the 12,705-foot Pearl Pass in Central Colorado isn't dangerous to most people, but you and your 4x4 are getting a taste of what these guys on Everest experience and there are some downsides. Planned for, these downsides can have minimal impact on your fun-time.
High Altitude and People
The effect of high altitude on people isn't from a lack of oxygen. The oxygen content at 10,000 feet is the same as at sea level, about 21 percent, but the air pressure is lower. Air pressure is what oxygenates the blood, so at 12,000 feet you're getting about 40 percent less oxygen with each breath than you would at sea level. To compensate, you breathe faster, but at some level of exertion, you will simply be unable to take in enough oxygen. So what's high altitude? Typically, the effects on people are minimal up to about 8,000 feet. Coming from the lowlands, your body needs time to acclimatize before you start exerting yourself. One to three days of taking it easy at, or near, the altitude you will be playing at is enough for most people. Some people take longer. Some people become very ill. Altitude sickness is serious business. There is no rhyme or reason to who it will affect. You can be an athlete and a perfect specimen of human health... and be laid low. Doubly irritating is the chubby couch potato next to you that's feeling fine. The symptoms are headaches; from mild to skull-splitting, nausea or vomiting, body aches, extreme fatigue, breathlessness and jumbled thinking. If you feel these symptoms, don't go any higher. Go back down to an altitude where you felt OK. The majority of the time, given time, your body will adjust. But in some cases, people don't adjust well or take too long to adjust and become impatient. There's really no point in suffering during a vacation, and pushing yourself can be dangerous. While playing at high altitude, drink plenty of water. You will naturally become more thirsty, and feeding that thirst will help alleviate the symptoms of altitude. A high carb diet is beneficial, so choose the pasta over the big hunk-o-seared meat. If you smoke, high altitude will get you to thinking about quitting. Finally, the risk of getting sunburned increases with altitude. Smear up with sunblock and sunblocking lip balm. Wearing sunglasses with UV protection is also important. Above all, avoid alcohol. The higher you go, the cheaper your "buzz." If you drink your normal sea level amount, it can have double the effect. "Whoopee," you say! No doubt some of you flatlanders are already packing the cooler with adult beverages and heading for the high country! Not so fast. The flip side is that you become much more impaired, so you ain't drivin'! Also, you haven't lived... or, should I say lived and prayed for death... until you've enjoyed a high altitude hangover. You'll be surprised to learn how little alcohol it takes to induce a hangover at altitude. Even people not normally disposed to them will often suffer.
High Altitude and Engines
Your rig suffers from the effects of altitude in many of the same ways as you do. Again, it's the decreased air pressure. An engine cannot inhale the same volume of air as it can in the lowlands. This drop in volume will decrease the dynamic compression ratio and change the fuel mixture. On engines that cannot compensate in some way, such as most carbureted and some older EFI engines, the fuel mixture will get increasingly rich with altitude... sometimes to the point of causing symptoms like flooding or fouled spark plugs. Even with mixture compensation, power loss is inevitable at high altitude. How much? The old rule of thumb says three percent per 1,000 feet above sea level. Some people disagree that it's quite so linear, but it seems to be accurate above 4,000 feet, You can build an engine for operation at high altitude, but most of you are looking for tricks that will help you run better for the short period of play in the mountains. A hot engine with a big carb and a long duration cam will be more affected than a stock or more mildly built engine. There is a practical aspect to making altitude adjustments. If you are cruising over the Rockies on I-70, you aren't going to stop for adjustments, but if you intend to 'wheel around Crested Butte for a couple of weeks, it makes sense to take the time to tune for the area.
Ignition Timing: If adjustable, advance it about two degrees for every 1,000 feet above 4,000 feet. Be sure to reset it to sea level norms when you drop back down or risk engine damage from pinging and detination.
Air Filter: A partly plugged air filter will really hurt performance when your engine is struggling to get a full cylinder of air as it is.
Carburetor: Unless you go to the trouble of installing high altitude jets, all you can do is readjust the idle mixture and idle speed. This will help a lot. Idle mixture has an effect on low speed off-idle operation, as well as idle quality. Usually, you'll end up having to bump the idle speed up a bit, and lean out the mixture by adjusting the mixture screws in.
High Altitude: Other Stuff
There are other effects of high altitude on your equipment, gear and provisions.
Air Compressor: If you have a compressor for tire inflation, you will find it's affected just like the engine. Expect tire inflation times to increase with increased altitude. The capacity of an air compressor decreases at about the same rate as the engine, namely about a three percent loss of cfm per 1,000 feet, felt most strongly above 4,000 feet.
Tire Pressure: Indicated tire pressure will change slightly with altitude. Thirty psi at sea level will read about 35 psi at 10,000 feet and vice versa. The pressure inside the tire doesn't change, but the external pressure decreases by about .5 psi per thousand feet of altitude. 10x.5=5 psi. This is most important going from high to low. If you set your pressure to 30 psi at 10,000 feet, it will be around 25 psi at sea level and perhaps too low and unsafe.
Exploding Munchies: Packages sealed at sea level will balloon up at altitude. No danger, but having once opened an inflated bag of Cheetos, only to be dusted liberally with Cheeto powder, has taught me to open bags, cans and packages pointed away from my face.
Drooling Sundries: Containers of sundry items like shampoo, hand lotion, etc, will build pressure as you climb. If it's laying horizontal, the internal pressure could forces the contents out into your baggage. If you keep the containers upright, with a little airspace on top of the contents, they can equalize pressure without spewing all over.
Fuel Cans: Fuel cans, with caps that seal well, filled at sea level can spray fuel when opened at high altitude. Not a good time to have a lit cigarette in your mouth.
