so , i was always under the impression that if a car was tuned for sea level and went to high altitude, it would run rich (less o2 at higher altitude...) and if a car was tuned at 5500 ft and went to sea level, it would run lean...

also, i was told running a bit higher boost , you can get away with at higher altitude because the cylinder pressure is automatically lower because of the thinner air (is overall cylinder pressure lower or just o2 content of the cylinder?)

in addition, if i am misunderstanding in the above statement, so if cylinder pressure is always the same and just the o2 content is less...would upping the boost at 5500 ft a few pounds (8-9psi)...be the same stress on the engine as say 6lbs at sea level??? my impression was the turbos just have to work harder to put out the same power at lower altitudes/lower boost levels...

could someone please give me a little lesson here?

THANKS

 

at high altitude you can run higher boost safely, but your car will not be faster. in fact, you will run slower. about 1 sec slower at 5k ft.

 

thanks for the input...but if anyone could elaborate and answer some of the points i asked...such as... is cylinder pressure at higher altitudes the same or lower as compared to sea level (or is just the o2 ammount lower at higher altitudes?)

 

At higher alt it is the lower atmospheric pressure that causes the lower output of motors. There is still 21% oxygen at any altitude in the atmosphere but due to the lower pressure (less dense) at higher altitude the total mass is lower thus less oxygen.

The reason you can run higher boost at higher altitude is due to the fact that (X) psi above ambient pressure is equal to (X) psi minus the difference between your altitude and sea level.

So for example 6psi @ sea level has the same mass (total number of particles) in each cylinder stroke as 8psi @ 5500ft. Thus the cylinder pressure is the same at 6psi @ sea level and 8psi @ 5500ft.
Gary

 

thanks gary... very informative ... the reason i ask is because i had a conversation with a tuner shop here in california (while visiting)...he said different... i explained to him my understanding... and he seemed to have the facts wrong... he must have read a different physics book

 

thanks gary... very informative ... the reason i ask is because i had a conversation with a tuner shop here in california (while visiting)...he said different... i explained to him my understanding... and he seemed to have the facts wrong... he must have read a different physics book