Originally Posted by GretchenGotGrowl
Maybe it is a placeholder and they will change it when a ZR1-like version comes out.
I think you can make any boost gauge show -PSI if you connect the reference tube to something that reads both boost and vaccum. I'm using an AEM TruBoost, so that's pretty common. If you hook it up directly to the turbos then you only read boost. If you hook it up to the manifold it will read both boost and vaccum. We hooked mine up to the manifold because I installed a vacuum pump and it gave me an easy way to adjust the vaccum I was pulling without installing another gauge in my car. Once I got that dialed in I just left it like that.
I know you can get it to read vacuum. What im saying is that -12 is not a number you will see on a gauge reading just PSI. 12inHg maybe since its reading vacuum but not -12PSI. The "-" on your boost gauge is just there to show you that the gauge is reading vacuum now. So -15 on aem truboost gauge is saying you have 15inhg. The positive number is psi obviously. I have never delt with those directly but have been told thats how it functions. Since its just leds and does not actually say "PSI or inHg" on the gauge. If it really was reading -15psi that would be a very unhealthy engine with very little vacuum.
Which brings me back to why the C7 gauge says PSI but yet have a negative number. Its probably just a placeholder though ya.