How much pressure builds up in the gas tank?

[banditt007]

How much pressure (PSI) actually builds up in the gas tank during extreme heat, sunlight/high ambient/running hard ext?

I'm wondering about the rule of thumb I heard of not going lower than 10 PSI on the pop off pressure and if thats due to pressure build up in the tank as a saftey issue or just general running/tuning problems that are encountered at that low of a spring pressure.

 

[CausticUC]

Thermal expansion of gasolines from 0 degrees to 30 degrees C - NIST PageView attachment jresv7n6p1133_A2b.pdf

 

[SteveSr]

How much pressure (PSI) actually builds up in the gas tank during extreme heat, sunlight/high ambient/running hard ext?

I'm wondering about the rule of thumb I heard of not going lower than 10 PSI on the pop off pressure and if thats due to pressure build up in the tank as a saftey issue or just general running/tuning problems that are encountered at that low of a spring pressure.

I think what you are looking for is called Reid Vapor Pressure. It is a controlled specification of motor fuels. Its value depends on the season and location. If your state has a motor fuels lab that would be a good place to start.

 

[banditt007]

Thanks guys it looks like it is in fact boarding just below 10 psi, so it seems the rule of thumb actually has some merit...

 

[SteveSr]

I'm wondering about the rule of thumb I heard of not going lower than 10 PSI on the pop off pressure and if that's due to pressure build up in the tank as a safety issue or just general running/tuning problems that are encountered at that low of a spring pressure.

Pop-off pressure is not tremendously relevant for saw carburetors any more. The main thing is that can hold back the tank pressure. You can damage the diaphragms in the carb by applying too much pressure attempting to measure the pop-off pressure.