Hi evoM,

I've searched, and though I've found the question asked, never found an answer due to threads being hijacked or going off on a tangent.

So, my minor gripe is that I bought an Evo at sea level. When I first bought it, the boost gauge zeroed when off. Then, I drove it home to Colorado where I live at 6000 feet. Now, the gauge zeroes into vacuum. This makes sense, as the atm. pressure here is less, and I'm working off the assumption that the gauge is mechanical i.e: not driven by a sensor output, but purely a hose connected to it.

Now, that's all great, but I want my gauge to show psig, which seems to be what it was designed to do, but only at sea level. I'm not so much worried about the zero when off reading, but the accuracy of it at max boost. Since I've heard the gauge is inherently accurate I'd like to simply change the offset between what it thinks local atm. pressure is and what it really is. Is this something I can adjust (shy of gutting the gauge and somehow reclocking the needle at ambient pressure here)? Is my best adjustment more likely relocating the HVAC and adding some "nice" gauges?

Any help appreciated. Obviously this isn't a life threatening situation, but it sure would be nice to fix this.

Thanks!

 

That's a good question, what kind of gauge is it and have u called and asked them about the issue? I've driven numerous cars with boost gauges that are off when engine is off, it's not really a huge issue especially on lower power cars if U ask me.

 

Move too a lower altitude.

 

I do not think the accuracy of the gauge is affected just because you are at altitude. When the car is off and the needle shows a slight vacuum that is, as you stated, because of your 6000ft altitude.

Because the gauge is mechanical and has been calibrated, it is going to accurately read whatever pressure it sees in the intake manifold regardless of elevation. I don't see how the gauge would have reference to atmospheric pressure to inaccurately read intake manifold pressure when the car is running.

 

This is the correct answer. The gauge is correct- you being at altitude means that there is less pressure. Inherently, one cannot consider a pounds per square inch of pressure accurate when there is a vacuum. PSI is generally accepted as a positive measure of pressure, and while we could consider "negative PSI" as anything below 14.7/atm (e.g. -1 PSI = 13.7psi, thereby below 1ATM), most gauges and instruments measure vacuum in a more undertandable measure against "Hg or inches of mercury.

I am not sure about this part, but I would assume that below what we would call "-14.7" PSI, the pounds per square inch measurement would not work. If I am incorrect or someone else would like to chime in additional information I am all ears.

 

Make sure you have the sender plugged in all the way or at least in the right place. When its running does it read vacuum.