Turbo boost gauge queery

[kfc]

Hi guys,
I think my gauge may be telling me pork pies, so in the interests of saving a few quid, would any of you chaps please be kind enough to tell me what your gauge reads when the car is at idle. my car has a hlm tune on it i dont know if that makes a difference.
Thanks in advace guys.

[LiamT4]

Should be about -14psi or something, its been i while though.

[kfc]

Just thought I best mention that its a S70R. Pre me7.

[LiamT4]

Just thought I best mention that its a S70R. Pre me7.

Not really that much difference between cars when at idle, sure my brothers 200sx is about -12or14psi.

[nobananas]

Shouldn't matter what the vehicle is or what state of tune it's in, all you are reading is manifold vacuum. Back in the 'old days' we used to tune motors using engine vacuum (amongst other things) as a variable, I remember setting contact breakers....... blah blah, dwell angles...... waffle waffle, balancing carbs ......drone drone, .....still had change from sixpence....etc etc

[960kg]

Myself being "old school" the vacuum at idle DOES matter.

Yes, it is only reading the vacuum in the inlet manifold but it does depend on the condition of the rings the valves etc. in other words if the vacuum is less the engine is not sucking so well so it is worn.

It depends what the compression ratio is and also how much carbon in the combustible space! So the reading does matter.


Engine Speed Gauge Reading Engine Condition
Idle 16" - 22" steady Healthy
Idle 14" - 20" steady Fair but worn
Snap throttle Jumps to 2" then on decel moves to 25" Healthy
Snap throttle Jumps to 1" then on decel moves to 22" Fair but worn
Idle 8" or less Vacuum leak, loose intake manifold
Idle Fluctuated between 14" - 19" Worn valve guides or head gasket blown between 2 cylinders
Idle Reading drops from normal Burnt valve, valve stuck open, misfiring spark plug
Idle 8" - 14" Valve timing incorrect or large camshaft overlap
Idle 14" - 16" Ignition timing wrong
Idle Moves between 12" - 16" Idle mixture incorrect
Slow engine speed rise Needle falls then rises suddenly Blocked exhaustWeak valve springs
3000 rpm Needle fluctuates and worsens with higher rpm Weak valve springs