[Vwdiesel] Altitude compensation
Roger Brown
r.c.brown at ieee.org
Fri Sep 2 22:50:50 EDT 2005
Libbybapa at wmconnect.com wrote:
> When I checked the compression on my TD vanagon all four were within 5 psi of
> each other. 3 were 400 and the fourth was 395. I was a little concerned,
> but the engine ran fantastic, so I've continued to drive it. My friend's
> quantum checked out at 380 on all four. I recently got thinking about the fact that
> I live at about 7,000 ft. When the altitude compensation is factored in to
> my friend's engine his compression at sea level is 460 psi. My TD vanagon
> engine would read 475-480 psi! Nothing wrong with that!
>
> I was also thinking about the recent discussion of Passats running on low,
> mid or high grade fuel. Someone mentioned that some people saw no performance
> decrease or mileage decrease with the lower grades, others saw significant
> difference. I got thinking that probably the cars seeing no change were primarily
> at high altitudes. I'd love to have that member of the group post that idea
> to the passat group. It makes me think that I've been wasteing my money
> putting high test in my ABA work van.
You can generally run 1 grade lower octane gas up high. My Toyota 4Runner takes 87, but when I hit the high plains and mountain
areas where 85 octane fuel is available, I use it and the engine works fine. In fact one time I was still running on 85 in the
tank by the time I got back to sea level and it ran fine. I do find I get better MPG at the higher elevations, probably a
combination of less engine power (ECU cuts back on fuel to match the lesser amount of air) and the thinner air has less density
and drag.
--
Roger
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