Chris, I used 15% as my guide between Bonneville and Lake Gairdner. Seemed to be
right for me. Ran just about the same speed at both places with good plug
readings. Doug Odom in big ditch
Chris Harris wrote:
> Thanks for the anology Mayf,
> A basic qustion from me while on the subject:
> With all conditions being equal ie temperature and humidity.
> How much less oxygen, percentage wise is available at 5,000 ft compared to sea
> level.
> Or another way, with a perfect EFI fuel map at sea level, how much do I lean
> (theoretically) at Bonneville with all other conditions the same apart from
> altitude.
>
> Chris Harris.......................NZed.
>
> Not having done this, only listening to you all, I have a coupla
> thoughts...
> 1) Assuming that the air pressure is about the same from morning to late
> afternoon ( It's not), and the air temp goes from about 75 in the morning
> to
> around 95 in late afternoon, then you will experience a decrease of
> approximately 3.6% in horsepower even if it is in perfect tune. Just a mass
> of air conition. Throw in the slight pressure change from morning to late
> afternoon, then the effect is a bit excerbated. The horsepower due to drag
> reduction matches the loss in hp due to density change, but there are a lot
> of things which say later is better: like reduced tire rolling resistance,
> warmed up components for greater clearances for less friction (albeit,
> small) plus maybe some other things. Now if you are running NO2 and/or
> boosted, you can make up for the power loss due to density change and take
> advantage of the less dense air for drag and go faster in the afternoon.
> So,
> NA run mornings, All others run afternoons, late..
>
> IMHO...
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