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Date:         Wed, 11 Jan 2012 09:53:00 -0800
Reply-To:     Don Hanson <dhanson928@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Don Hanson <dhanson928@GMAIL.COM>
Subject:      Was:Re: Oil in Coolant Morphed to "Power at Altitude" or
              something like that.
Content-Type: text/plain; charset=ISO-8859-1

On Tue, Jan 10, 2012 at 6:22 PM, Larry Plotkin <zeplotkin@gmail.com> wrote:

> Finn wrote: > > Klip, klip ... > ... I moved from NJ to Taos, NM ... At 7000 feet here in Taos, I believe > that the hp loss is around 21% ... Is there anyone listening that is at a > similar altitude... I > would have no problem getting to say 75 mph at sea level in the 87... > > Well, I have no tech help for you but ... I ran my 87 Wolfy hardtop 4sp > (stock everything except 27x8.5 14 tires) in the northwest near sea level > for 11 years and then moved to the AZ mountains where I've been for nine > years, at 7000 feet. I changed nothing, adjusted nothing, and noticed no > change in performance. 75 is easy as ever. Coming up here from the desert > ain't fun, a crawl in 3rd gear often, but climbing near 6000 feet in two > hours, that just goes with the vehicle. So I guess I'd be looking for > something to fix, not an inherent limitation of elevation. > > (And I guess I'd have to add that Taos must be way better than anything in > NJ, at any speed.) > lp > There is a significant loss in power from any internal combustion engine as altitude increases.. Someone will probably know the numbers exactly but I'd guess about 20% power loss at 7000' above sea level as compared to sea level on a normally aspirated motor is about right. Forced induction motors are less affected by elevation gains, and of course, engines with carbs...they are more affected than fuel injected motors.

Combustion in the motor is very dependent on oxygen and simply, there is less oxygen as you gain elevation...A turbo or supercharged motor can adjust and pack in more combustable mix...maintaining better power as you gain altitude. A fuel injected motor can adjust it's mixture to compensate for less oxygen, keeping the air fuel ratio correct as you climb up...but it must just diminish the amount of fuel to compensate for the diminished oxygen in the atmosphere. A carbed motor loses power two ways in that there is less air to burn stuff AND since it doesn't adjust to this...the air fuel ratio gets 'out of spec' and it runs rich, further losing power that way.

If you doubt this...check it with a watch or something next time you go from ocean to mountains...do a simple 0>75mph timed run both places and you will certainly find it takes significantly longer at elevation to reach your target speed.

On a side note: I have noticed a significant increase in miles per gallon at higher elevations in my inline Jetta gas motored vanagon....I get around 23mpg as my normal fuel consumption overall, but when I venture into the high mountains I have seen fuel economy jump to(max) 26 miles per gallon on several occasions... Wonder what causes that, exactly?

Don Hanson


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