Alan Myers wrote:
> Listerati,
>
> Ok. I am not an engineer. Ergo, when these discussions get into
> exponentials and laminar flows, this red haze starts to descend on my
> vision.
>
> So I have a PDQ (probably dumb question) regarding altitude above sea
> level, please be kind and only mildly scientific in any responses.
>
> Everything else being equal, is a carburated car more or less likely to
> knock (or ping) as a factor of octane at high altitude, as opposed to
> sea level? Or, is this a neutral consideration, with leanness and
> richness of the mixture being the primary (or only) variable with
> altitude due to the difference in air density?
>
> Alan Myers
> San Jose, Calif. (sea level + 50 ft)
> formerly of Colorado (sea level + 6000 ft)
> '62 TR4 CT17602L
>
> --
> MZ
Alan,
Provided that the carb is tuned properly, the higher you go in altitude,
the richer the F/A mixture will get. When engines run rich F/A ratios,
the engine runs a bit cooler due to the unburned fuel absorbing heat from
the combustion process.
If a carb is tuned properly for a high altitude (say Colorado) and is then
driven to a low altitude area (say San Jose), without the carb being
re-tuned, the engine will run lean F/A mixture. Lean mixtures tend to run
hotter than normal and can cause knocking.
Re-tune your carburetor for the lower altitude. Once properly tuned, you
should notice a increase in performance. The numbers that I have seen is a
change of 10% in Horsepower for every 3000 ft of altitude change.
--
Patrick Barber, Allen Park, MI
70 Spitfire MkIII FDU89984L
74 Spitfire 1500 FM14774U (Organ donor)
Visit My Triumph Website at
http://www.geocities.com/motorcity/pit/7864/Triumph/
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