FC3S Murray's never ending build.

[MaczPayne]

Originally Posted by TitaniumTT

Hey Johnson, I've used that site alot but it doesn't make any sense whatsoever. The less kpa you have, the more vac you pull. 100 kpa = 1 bar = 0 vac, 0 kpa should = perfect vac or about 30", so what are we missing here?

This is very tricky to explain. I've probably typed and deleted a whole bunch of sentences just because they sound confusing.

"The less kpa you have, the more vac you pull." This is true, only if 0 is perfect vacuum, and any value above that is pressure. What's missing is the idea of reference zeros. Our boost gauges put the reference at atmospheric pressure (1bar, 100kpa, 14.5psi). Below that point is vacuum, usually measured in inches of mercury, for standard units. 30" Hg = 0psi absolute = 0kpa absolute = -14.5psi = -100kpa = -1 bar.

You might be wondering, "why is 30" Hg positive then?" I believe the reason for that is units for above atmospheric pressures are different. If boost read in " Hg, vacuum would then read in - " Hg. Also the generally accepted standard unit for vacuum is inches of Mercury, which is why negative signs are neglected.

My boost controller reads in psi, so in vacuum, I'm somewhere around -7.3 psi, for example.

Hope this explanation helps. I can help clarify any other details if you so inquire. I am most likely still editing this as you read, heh.