Vacuum at idle
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There is a difference between psi and inHG. An accurate vacuum gauge is not something most have. Boost gauges tend to have have 2 scales, psi for positive pressure and inHG for negative pressure. Any multi cylinder engine should be steady at 18-20inHg at idle, sometimes slightly higher. Increased cam overlap or altitude above sea level will reduce.
My old 71 340 Small block Chrysler with a 284deg duration cam idled around 12-14 inHG.
My old 71 340 Small block Chrysler with a 284deg duration cam idled around 12-14 inHG.
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Realized my Autometer needs to be recalibrated, it sits at about 4 psi when the engine is OFF instead Of Zero. Did some reading and it seems to be common with this gauge. Its an easy fix, and explains why it was sitting at -13 inHg at idle. Guess thats what I get for buying a $50 boost gauge lol.
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Mine specifies inHg for vacuum. Its definitely off, as it doesn't "zero out" when the engine turns off as it should. It sits at about 4psi when the engine isnt running, i just didnt notice it before. But yea I read psi conversion charts and 1psi is equal to 2.03 inHg, so Moddiction and the others using the AEM gauge should be right on the money if it reads in psi.
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