On the flat at 75 ish mine reads just under minus 7psi or minus half scale. Foot off decelerating gives almost -14psi. Is this about right? I remember reading a long time ago that the degree of vacuum pulled on closed throttle is a good indication of the condition of your piston rings and bores. So should it go to -14 or lower on foot off over-run? and is higher a bad sign?

So long as you arnt taking the reading from the standard boost guage in the dash.

It is notoriously inaccurate.

How inaccurate is Notorious?

When its on foot to the floor it makes 3 notches goes like hell and implies +10.5psi. This kinda lines up with the Stillen chart for exhaust and intake mods. When I didnt tighten up one boost pipe properly after cleaning the throttle bodies it struggled to +7psi and not same urge cos air pressure leakage. So I am reasonably happy with what it reads when all is tight. Who's to say the after market guages are just as inaccurate. I would defo say the oil pressure gauge is inaccurate because that changes day to day. Seems higher when it rains for example. Can nearly hit 90psi cold and never goes below 15psi but that has electric sender whereas boost guage is mechanical I think.

well according to my blitz id metre which has an electrnic readout, my stock boost guage is waaaaaaaaay off.

i also have a blitz 60 mm boost guage.

and that works fine and basically very accurate when compard to my id metre.

IE if i have .6 bar or roughly stock boost set on my id metre, my blitz boost guage reads .6 bar my stock is of the scale.

Originally posted by WillieO:

whereas boost guage is mechanical I think.

 

FYI the boost guage is electrical - there is a sender top left corner of the engine bay..

And they are hugely innacurate.. Aftermarket guages are a lot more accurate - depending on how much you pay..

 

Az