docwyte

Ok, I've always assumed that with a boost controller set to 15psi, the car will boost to that regardless of altitude.

A person has recently told me that at altitude, even if the boost gauge is showing 15psi, if you put a MAP sensor on the car it'll show 3-4 LESS psi than the boost guage will show.

Ie, that you're really only making 11-12 psi, despite the 15psi shown on the boost gauge. (Which happens to be tapped off the intake mani, btw)

I personally think this is a crock, but they guy swears he's validated this on the dyno.

Can anyone else support this? Am I full of it?

Yabo

I thought altitude did matter, because of air density. I thought 15PSI at lower altitude will have more oxygen molecules (which cause the power increase) than 15 psi would at a high altitude?

dont take any validity from my answer,, i really have no background on it..

Perry 951

Pressure may still be the same at different altitudes, but mass will be different. Same concept as cold vs hot air. Colder is more dense, as is air at sea level.

We also have altitude compensation boxes in our cars that should assist with ignition timing as well as fuel.

docwyte

Ok, that's what I thought. Power would go down, as it would on a naturally aspirated car (more so for them) but boost pressure would be the same...

theedge

Tell him to share what hes smoking. Why is a boost gauge going to show differently than a MAP sensor? Did he explain that? Even the stock gauge is driven off a MAP sensor in the KLR.

Unless this is Autometer striking again...

docwyte

This isn't on a 951, although it shouldn't matter, boost is boost, regardless of the car...

theedge

Exactly, unless what he is talking about is measuring before and after the intercooler and thus pressure drop.

GodSpeed

this is a true statement. the air will be less dense due to the atmospheric pressure change but you will still get 15psi for your turbo.

CO951

The density of the air with 15psi boost at 6000 feet is probably close to the denisty of the air with 11-12 psi boost at sea level. That maybe what he is thinking, but that is far from what he said.