We have two cars: a 1989 Volvo 240 and a 1997 Toyota Tacoma. We
recently moved to Maryland (roughly sea level) from the Colorado Front
Range (elevation roughly 5,300 feet.) Both our vehicles were
originally sold in Colorado.

We were wondering if it is necessary to get any adjustments made to
the engines of either car because of the change in altitude. For
instance, some people have speculated that cars sold at high altitude
have their fuel/air mixture optimized for this altitude. Is anything
like this true? Is there something we should do to our cars, or do the
vehicles need no adjustment whatsoever to perform optimally at lower
altitude?

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Request for Question Clarification by gan-ga on 02 Nov 2002 12:35 PST

Hello massysett,

Certainly, the change in atmospheric pressure with altitude means that
a basic piston-type internal combustion engine will run most
efficiently when it's carburettor jets are of the correct gauge
specified for the band of air pressures likely to be found at a given
altitude.

Other factors apply though..

The above only applies to engines fitted purely with a fixed-jet,
simple carburettor. This often does not apply to modern vehicles,
which may use instead, variable venturi or variable jet technology (or
a combination of the two), which goes some way toward automatically
compensating for altitude.

Also, fuel-injected engines generally have their intake fuel-air
mixture controlled by an onboard computer, which in many cases uses a
measurement of air pressure as one of it's inputs - in this case,
there is no need for adjustment as such, as the computer is
continually 're-tuning' the engine.

If you could clarify your question by telling us the exact engine type
fitted in each car (more than likely the exact car model would
suffice),
for example '1997 Toyota Tacoma 4x4 XtraCab with ?.? litre twin
carburettor engine' (a ficticious model for illustrative purpose
only..), myself or another researcher may be able to check on the
details and provide you with a definitive answer.

hope this helps,

gan

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Clarification of Question by massysett-ga on 04 Nov 2002 07:02 PST

Hi gan-ga,

Thank you for the clarification request. The 1989 Volvo 240DL is a
4-door sedan. It has a 2.3-liter 114 horsepower four-cylinder engine.
It is fuel-injected.

The 1997 Toyota Tacoma is an x-cab, with a 2.7-liter four-cylinder
150hp engine. It is also fuel injected.