Date: Sun, 1 May 2005 09:37:23 -0500
Reply-To: John Rodgers <inua@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <inua@CHARTER.NET>
Subject: Re: HELP! Westy Stranded in Bryce Canyon National Park...
In-Reply-To: <e0.12b2c0a8.2fa5c580@aol.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Not to beat this to death, but....
If I understand our vans and the FI systems, the ECU has sufficient
capacity to maintain proper fuel/air ratio regardless of altitude or
temperature.
A hot summer day at altitude would be the worst of all conditions, as it
would tend to send Density Altitude right off the scale. 10,000 feet ASL
becomes 12,000 feet ASL at a high temperature - for performance
performance purposes. If the engine is in good condition, proper
condition, at sea level, then at those higher density altitudes the ECU
should be able to maintain that proper fuel/air ratio.
The problem of decreasing performance at altitude is due to the fact of
less dense air. As the air becomes less dense, the engine ttends to run
more and more rich as altitude increases. The ECU adjusts the fuel air
mixture to proper ratio, but it does it by reducing the amount of fuel
to match the air available. At altitude with the air thin - less oxygen
per pound of air than at sea level - the reduction of fuel to match
results in a power loss. So if you van is very peppy at sea level, don't
expect it at altitude, especially out in the west in summer.
As a side note, the Density Altitude is a matter of serious concern to
aircraft operations. Lift generated by the wings of the aircraft is
related to speed, and an airplane must have sufficient speed to lift off
the runway and to gain altitude. At high density altitudes the airplane
must have a runway long enough to allow the airplane to accelerate to
the higher speed required. To accomplish that higher speed, it must also
have sufficient engine power. With the loss of power, from the effects
of altitude and temperature, combined with the need for additional speed
to achieve liftoff velocity, and the subsequent additional runway
required to allow enough time to reach that liftoff speed, it can become
very problematic for an airplane to even be able to get off the ground.
So, there are all kinds of tables, charts, and considerations for a
pilot to make or refer to , so as to be able to make a decision about
the safety of the flight about to be attempted. One of the first steps
to attempt to overcome such difficulties was to add a supercharger to
the engine to get the power back up. With a supercharged engine, the
power is maintained, acceleration is faster, and lift can be achieved to
get the airplane off the ground within the confines of the runway. Later
came turbine engines, which improved matters even further. But even so,
pilots to this day must be concerned about the relationships of
temperature, aircraft loaded weight, engine power available, etc.
How does all this relate to the Vanagon. Expect less power at altitude
unless the engine has been turbocharged. That is the main thing. One
might also expect an increase in gas mileage at altitude - high density
altitudes mean lower air resistance....plus the reduced fuel consumption
when the ECU reduces the fuel to keep the fuel/air ratio correct. But
again, if the engine is turbocharged, sea level power could be
maintained so fuel consumption would not change. Gas mileage might
improve slightly due to lower air resistance.
My $0.02 for the morning.
John Rodgers
88 GL Driver
Chelsea, AL
Jeff Oxroad wrote:
>In a message dated 4/30/2005 5:14:06 PM Pacific Standard Time,
>camper@TACTICAL-BUS.INFO writes:
>
>Here in colorado it is possible to get different blends according to the
>altitude. But that blending is for emissions and your engine should run the
>same either way if the O2 and AFM and ECU are working correctly.
>
>
>
>I have to respectfully disagree, and I do so with no ill intent and no ill
>will. But instead to set the record straight.
>
>You are correct that the high-altitude blend of gasoline has a posative
>effect on emissions. However the theory that there's no effect on the engine's
>ability to run correctly doesn't fit the above conclusion. The idea that a
>different blend effects the emissons but not how the engine runs is flawed. This,
>because how the engine is running is directly responsible for the emissons.
>A "correctly" running engine--one running under ideal circumstances-- will
>produce lower emissions than one running under poor conditions. The
>configuration is also then contigent on the blend of gasoline and the altitude.
>
>The gasoline blended for a specific altitude is concocted with consideration
>to the amount of oxygen in the air. The guy who's stuck in Bryce is very
>possible having a problem related to the fuel system. He stated he can smell
>fuel. Therefore let's say for arguments sake his bus is getting too much fuel
>for the amount of oxygen at the altitude were he is camping. This is likely
>because the fuel in his tank is mixed for a lower altitude. In essence the
>engine is getting too much fuel to start--it is "flooded." It is running rich we
>would say if it were running. or now we can say it's too rich to start.
>Why--because they're ain't enough oxygen to create a favorable situation for
>combustion with the higher octane fuel. (and I'm not willing to agree that the
>difference in the high altitude blend of fuel is soley an issue of octane.
>Although this is certainly the most notable difference to the consumer since it is
>printed at the pump.)
>
>Granted this lack of combustion--or even if he got the engine to
>tstart--creates an unfavorable emissions output. But this emissisons problem is
>precisely the same problem that is keeping the engine from starting: poor combustion.
>One is the same as the other.
>
>I would almost agree that if everything is working properly this might not
>be a crucial concern. So I'd say if the guy stuck in Bryce drove his Westfalia
>off the dealer's lot in 1984 and headed to the Canyon with a lower altitude
>fuel he'd likely be up and running and we wouldn't be here hashing this out.
>But 21 years after that bus came off the lot, that extra rich mixture might
>just be enough to leave a guy stranded. And quite frankly it may have been
>enough to leave him stranded him in 1984.
>
>Therefore I still recommend fueling up every 1,000 feet you gain in
>elevation. Also a fresh tune up when heading to a higher altitude will help.
>
>Disclaimer: The fellow in Bryce Canyon could be suffering from a host of
>problems. The altitude vs. gasoline is not necessarily it. But it's worth
>examining.
>
>Best,
>83.5 Westfalia
>LA,CA
>
>
>
>
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