OK, dumb question time. I was arguing this with a friend last night, maybe you can tell us who's right.

Example, Say I'm running 8 pounds of boost at sea level then I travel to Denver. If I change nothing on the car, will I still make 8 pounds of boost in Denver?

If yes, will the 8 pounds of boost in both places have the same air density (assuming that the temps, humidity etc. are the same)?

If no, why the hell not?

 

not sure about the psi but the air density will be thinner in Denver because of the higher altitude. Its the same reason why mountain climbers have to wear air tanks, becuase the higher you go the thinner the air gets

 

I tend to agree. So based on that would it be safe to run higher boost levels at higher altitudes than you normally would at low altitudes?

 

If you put 35PSI in a tire, and the car is in Baltimore (sea level), the tire will have 35PSI.
If you put 35PSI in a tire,and the car is in Denver (aproximately 5,200 feet), the tire will have 35PSI.

Same with 8 pounds of boost.

 

do a search on boost and altitude, I'm at 5500ft in ALbuquerqe, and I have started several threads on this topic....

the turbo will still make 8psi, it wil just need to spin faster, compress more of the thinner air to reach the 8psi...also, depends on what your boost gauge is setup at..most mechanical boost gauges assume "0" is atmospheric pressure, or 14.7.... up here at 5500ft, atmospheric pressure is about 12.2, this also changes a few things regarding reading the boost

-TODD

 

Goes for Vacuum also

 

8psi is 8psi is 8psi no matter what altitude. The turbocharged motor is unafected by altitude until turbocharger runs into inneficiency issues @ higher rpm or the wastegate is completely closed and can no longer regulate boost.

Humidity does not change air density. Humidity level is not a factor influencing performance in regards to engien output.

JET

 

No argument on this statement, but I've heard (maybe incorrectly) on a pretty consistent basis that if you're running a xxxx size pulley on a SC that is supposed to generate xxx psi of boost at sea level, the actual amount of boost you will generate at altitude is indeed less (assuming nothing else is changed). My guess is this is what the OP was getting at???

 

Superchargers will have a loss of boost with an altitude increase. That is a true statement.

JET

 

the boost level will not change. and yes, it is safer to run more boost at altitude. cheers!

 

That's an incorrect statement.

JET

 

So back to the density portion of the question. Would the 8 pounds of boost in Denver (assuming that all other factors are the same) be at the same density as the 8 pounds at sea level?

I guess what I'm asking is, what is the 8 pounds referenced to? Is it to the ambient pressure of wherever you are at or is there a universal standard?

 

PSI is a measure of density by weight. Pounds Per Square Inch. So your asking does a pound of feathers weight the same in Boston as it does in Denver. I think you can answer that one.

JET

 

AHHHHH --HMMMMMM ??? Are these downy feathers or like --dip in the ink and write stuff feathers ???? Have these feathers been taken from a willing or unwilling recipient ??? And if unwilling---Has the recipient been traumatized ???

 

Density is a measure of mass per volume. PSI is a measure of pressure isn't it? What you describe, it seems to me at least, would be something like pounds per cubic inch.

 

PSI = POUNDS per square inch. POUNDs is a weight measurment. The question you are asking is how much does 8 pounds per square inch weigh. 8 pounds per square inch of air weighs 8 pounds per square inch. It's as simple as that.

JET

 

But it's not what it weighs. It's the amount of pound-force (force and weight being totally different principles) that it is exerting on a given square inch of surface area. In order to weigh something you have to have a defined volume.

Edit: I could be way off base here, I've been out of school for a while. But this is the way that I've always understood it to work.

 

The atmosphere is the defined volume. The atmosphere exerts 14.7psi at sea level at 29.92 hg at 59 degrees farenheit.

I can't go into the basics of atmoshperic affects on engine performance in a message group. You could find a book or video on flight physics and performance and it will explain everything to you.

Here are the facts summarized. Altitude has no effect on turbocharged engines until the wastegate has reached it's fully closed position and can no longer regulate boost. Any altitude increase at that point will decrease the power of the engine. Supercharged motors lose perfromance with altitude at the same rate a naturally aspirated motor will.

As altitude increases the wastegate regulates 8psi of turbo boost by opening later and dumping less exhaust. Due to the thinner air of the atmoshere as altitude increases the compressor encounters less resistance/friction from the thinner air and spins faster to create the same amount of boost.

JET

 

Ok, I see what you're getting at. BUT!

At sea level let's lets say that you have 14.7 psi of atmospheric pressure add our 8 pounds of boost to that and you have a net 22.7 psi.

Now we go to Denver where atmospheric pressure should be slightly less than an atmosphere. Let's just pretend that the atmospheric pressure is 14.2 there (because I have no idea about what it actually is) that gives you a net pressure of 22.2 psi.

This is where I am getting confused. Wouldn't the boost be indexed to the atmospheric pressure of where you are actually measuring it?

 

The question is "Does the atmosphere in Denver contain the exact number of oxygen molecules CORRECTED for barometric decrease as the atmosphere at sea level.
Denver is about 0.85 of sealevel so normal Denver pressure is 12.5 psi and you would need 2.2 PSI more boost to equal the same power at sealevel.

http://www.phoenixelectrode.com/lvl2/oxygenguide.html

A pound is not the same everywhere on earth as gravity varies around the earth by up to 1%.