Frank Crowe wrote:
>
> > Shawn said: "The high point of the road is 12,183 feet."
> > Peter Zaborski said: "How do the non-computerized cars deal with that
> elevation?"
>
> I just went over that pass a few weeks ago on a trip 'cross country, but
> was driving an injected Volvo (those injection systems amaze me at how
> well they work at any altitude or temperature.)
Barometric compensation can be accomplished in a number of ways with
fuel injection, and most do fairly well at it... the injection system
can lean the mixture proportionally to the barometric pressure, but just
can't compensate for the lack of air. Even for an injected engine which
is metering fuel accurately, the power loss without turbo or
supercharging is considerable. Air density drops by about 3% for each
1000 feet above sea level, so at 12,000 feet, the engine can produce
about two-thirds of normal power in a given rpm range. What makes
carbureted cars suffer even more is the progressive richening of the
mixture in the upper rpm range (where it is producing maximum power or
close to it) due to Bernoulli effects.
> As I was climbing toward the top, I was also thinking how my TR3 would
> be doing at over 12K'. Shawn, please discribe how LBC's do where a good
> portion of the earths atmosphere is below you.
In general, the cars don't do well at altitude, unless jetted for that
altitude. Mine is cobbled a bit (lower float level to compensate for
richer jets) and seems to pull okay, but not dramatically, up to around
8,000 feet. I have driven a rented Nissan, carbureted, and jetted for
Albuquerque (5200 ft) over the pass between Taos and Santa Fe, and that
is close to 10,000 feet. And the little beast was really struggling...
although it would do fine at 7,000 ft.
In short, properly jetted, a 100 hp engine will make about 65 hp at
12,000 feet, so the performance will be modest at best.
Cheers.
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