Pike's Peak and Fascination with Impending Vapor Lock

I doubt you can see the "Pike's Peak Summit" sign behind us, but it's there! We made it up to the summit, despite having no generator running, by leaving the motel early. We were the first people at Pike's Peak to start the ascent to the top. The drive is 19 miles and goes from around 7,000 feet or so to 14,110 feet. The boiling point of water is lower at higher altitudes, so I looked up that table night before and was discouraged to see that water's boiling point at 14,000 feet is 85C, which is just 2-3C higher than I normally run, but driving up the mountain would push up our temperature higher.

I kept it in second gear most of the time, sometimes going to third on the flat or even short downhill sections on the way up. The water temperature was good, but then we started hitting the switchbacks which forced us to drop to about 5-10 mph on the hairpins, so the low RPMs and heavy work caused the temperature to rise. I thought about trying to get all the way to the top without stopping, but the temperature was at 93C so we stopped at 13,000 feet and milepost 16 (Devil's Playground). The water was boiling but hadn't purged any out, so I opened the cap and let the pressure vent off and we waited 30-40 minutes for the water temperature to cool to 84C. From there we made it up to the top with no further issues. Our final accomplishment before coming home.

The fascination with vapor lock will likely fascinate no one but me, but for those interested, read on:

Given: My generator is dead.

Given: Besides ignition, unless my lights are on the only other real draw on current is the fuel pump(s).

Given: The standard dual-SU fuel pumps draw current only when they're clicking. They click to suck fuel when there is not sufficient pressure to the carbeurator (~3psi). You can see this amperage draw by watching the ammeter.

Given: When I turn on my auxiliary pumps, they draw a constant amperage, therefore the ammeter is steady instead of the bouncing of the ammeter seen when running just the SUs.

Given: If I have vapor lock, I turn on the auxiliary pump which overpowers the dual SUs, therefore the ammeter shows no bouncing because the dual-SUs don't have the need to provide any fuel.

If I am running the auxiliary pump and the conditions are such that I still encounter vapor lock, suddenly the SUs realize they need to provide fuel. They aren't going to be able to do much, because if the more powerful auxiliary pump can't do it, they're not going to be able to compensate.

What fascinated me was the following. As I'm driving down the road with the battery continuously discharging and the auxiliary pump on, the ammeter reads a constant 0.5A discharge. When it was hot out today, if I put down too much power (fuel demand), I could watch the ammeter stop reading constant and start bouncing -- indicating impending vapor lock. The dual-SUs were trying. But when it gets *really* bad, those dual-SUs start working like mad, a constant clicking, and when that happened I could see it manifested in the ammeter no longer bouncing, but a constant discharge of about 3A. Now I knew we were just about to start feeling the vapor lock.

The drive today through the heat consisted of me trying to walk that knife edge. How fast can I keep going without experiencing vapor lock? It was so easy to see now. This is the surface curve I was talking about in a previous post. If the ammeter started bouncing, I could drop the MPH by 1-2 and be safe, discharging at a constant 0.5A, safe from vapor lock. It was like a game, and while we sometimes had to drop to about 45mph on the interstate on the longest upgrades, we never had vapor lock hamstring us.

I don't know if that was interesting to anyone else, but watching the gauges (ammeter, temperature, speed) and the traffic is a very different way than just driving our modern cars. It really is entertaining, although I have to say that I really wish my generator were working.

Tonight I pondered continuing on through the night, but surely the lights would have drained both of my batteries quickly. So we're stopped relatively early tonight and will get up and get back on the road before it gets hot tomorrow...