Discussion and questions related to the course EFI Tuning Fundamentals
Might be a stupid question, but can someone explain in a little more detail how absolute pressure gague reading 40.7 psi and when connected to a tyre with 35psi of air in in would measure 49.7psi in absolute pressure.
I cannot get my head around it.
The world is in a constant pressure (barometric pressure), which is 14.7 psi at sea level on a good day, on a gauge it will read 0psi.
absolute pressure = gauge + atmosphere
So for your example, the gauge pressure of the tyre is 35psi but for the total pressure (absolute pressure) it is 35psi+14.7psi=49.7psi if you were at sea level, if you are at a higher altitude or in a weather system with a low pressure then your atmospheric pressure won't be 14.7 any more, it could be 9.7psi. 35+9.7=40.7
it's either that or the gauge is faulty.
EDIT: it's also worth noting that pressure gauges for tyres are reading the pressure differential, the difference in pressure from the inside of the tyre to the atmosphere around it