Could you please tell me the PSI you are running at the following RPMs and Speed on your EVO?

70 mph
75 mph
80 mph
85 mph

AND

2500 rpm
3000 rpm
3500 rpm
4000 rpm

EDIT: Since some of you have asked for clarification here it is:

05 EVO with Cat-back exhaust
Cruising on a flat freeway to maintain a constant speed of either 75 or 80 mph

 

as soon as i get my logger fixed i'll post up a chart

 

that's gonna be based on load, mods, and throttle position. IE, more boost going uphill than down.

 

Stock car or Exchaust only, freeway cruising at constant speed.

 

Mabey im reading this wrong but if your cruising at a constant speed wouldnt you be off boost.

 

regardless, it's still dependent on what avengerhed said...i would say vacuum-zero based on "cruising speed" which I take as constant velocity. How is this information useful other than seeing if your boost gauge is not reading correctly?

 

OK, let me try it this way. What will the boost gauge read when I am cruising at 75 mph on the freeway? The gauge should read something, what is it?

 

All lot of people say stay out of boost if you want to save gas. I want to know what is the boost reading at those speeds/rpms.

 

Gauge will probably read -0.4bar (-5 to -6psi) or so, depending on how you are cruising. Even the slightest change in throttle position will change the reading quite a bit as previously discussed.

This is assuming 5th gear on a 5MT Evo. It's also assuming your car is similar to mine.

 

-.4 bar! Holy vaccum batman!

Vaccum is rated in measured in in. Hg, not psi

 

^^ theres no such thing as negative boost (neg psi)

what you will be reading is vacuum as you are coasting...which you will be reading in "Hg (inches of mercury)...this is actually a positive number although it will look like a neg number on your gauge b/c it will be below the ZERO point of pressure

while coasting (with your foot OFF the throttle) you should read 22-26 "Hg or thereabouts

but im really not quite sure what you are asking or why you are asking it

 

Bolsen, He is more right then you are. It is an absense of pressure not really vacuum.

To the original poster. If you are cruising at 75 mph then the boost guage will not be reading anything since you will not be in boost. If you are then you are accelerating.
Especially stock. What you are asking is boost so I assume you are only looking for positive readings.

 

What is the point of needing to know this?

My car at any "cruiseing speed" not accel not decell im at 10 Hg or so
With Zero throttle its around 22ish as stated and when full throttle well its pulling into PSI as it should

but this kinda seems like a pointless thread to me

 

One last word on the vacuum thing. Remember that guages are corrected to be relative to atmospheric pressure not absolute. Therefore it is really not vacuum unless we are talking 29+ in. of mercury.

 

why is it measured in vacuum?

the absense of pressure would just read zero would it not?