Jump to content
SAU Community

R33 Gts-T Vacuum At Idle

insert

By insert,
in Engines & Forced Induction

 Share

Recommended Posts

insert Contributor

insert

Posted
Posted

hi all,

recently bought the car. it has a drift iridium (digital) boost gauge. ad idle its reading -18psi. is that a normal/correct reading, or is the gauge malfunctioning. for some reason i think it should be reading less.

the car is pretty much bone stock mechanically save for a CAI, exhaust, intercooler, boost controller (running stock boost level).

forgive me for my ignorance, its my first r33.

thanks

Link to comment
https://www.sau.com.au/forums/topic/381472-r33-gts-t-vacuum-at-idle/
Share on other sites
GTSBoy Grand Master

GTSBoy

Posted
Posted

Yep Psi is a measure of positive pressure

And negative pressure. Pressure units are quite universal. It's just that manifold vacuum is traditionally read in some of the more bullshit units like inches or mm of mercury. It shits me to tears that whilst we have a perfectly good set of self consistent SI units for pressure (Pa, dPa, hPa, kPa, MPa) that people continue to talk in rubbishy units based on the column height of some randomly selected fluid like mercury or water. It's time to come kicking and screaming into the 20th century is what I say.

zebra Grand Master

zebra

Posted
Posted

Isnt it because Mercury isnt affected by air density as much?

Therefore measuring head flow in mmHg or inHg is more consistant, rather than saying x port flows y cfm at 22.14646363 deg C and 1009 QNH.

I think...lol

89CAL Grand Master

89CAL

Posted
Posted

I've seen mercury and water used, there is a reason i just dontt remember

A negative psi value does really exist. you can't have below 0psi in a vessel. 0 pounds/square inch

Remembering that 0psi on your boost gauge is still 1atmosphere

GTSBoy Grand Master

GTSBoy

Posted
Posted

A negative psi value does really exist. you can't have below 0psi in a vessel. 0 pounds/square inch

Remembering that 0psi on your boost gauge is still 1atmosphere

Yeah you can. Absolutely no reason why you cannot express it in psi. The positive pressure is outside the vessel.

psi is a measure of force (pounds force) per unit area (square inch). So is any SI unit. The Pascal (Pa) is defined to be one Newton (force) per square metre.

same same. Just that SI units don't suck because they are easily convertible from one to another without having to use/remember arbitrary conversion factors. And the mmHg and mmH2O units require that you use the force of gravity to convert them (9.807 m/s2) which is gay, and is not universal because the same real pressure would give you a different fluid column height on a different planet (or even a different height on different parts of Earth where the force of gravity is slightly different from elsewhere. It is a very small difference though!)

cheers

GTSBoy Grand Master

GTSBoy

Posted
Posted

Makes no difference whether you're talking absolute or gauge pressure. It's all pressure. If you totally evacuate a volume you have zero absolute pressure in it. That's zero psi, zero kPa, etc etc. The gauge pressure (relative to 1 atm pressure outside the vessel) inside is -1 atm, -14.7 psi, -101.325kPa (assuming we're at sea level of course). Let a little bit of air in there, and you might have a pressure of 1 psi absolute, -13.7 psi gauge.

cheers

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • GTSBoy
      RB20DE NEO smallbox clutch.

      By GTSBoy · Posted

      Input shaft bearing. They all do it. There is always rollover noise in Nissan boxes - particularly the big box. Don't worry about it unless it gets really growly.
    • Kapr
      RB20DE NEO smallbox clutch.

      By Kapr · Posted

      For once a good news  It needed to be adjusted by that one nut and it is ok  At least something was easy But thank you very much for help. But a small issue is now(gearbox) that when the car is stationary you can hear "clinking" from gearbox so some of the bearing is 100% not that happy... It goes away once you push clutch so it is 100% gearbox. Just if you know...what that bearing could be? It sounding like "spun bearing" but it is louder.
    • GTSBoy
      Mistakes were made, my R34 Story

      By GTSBoy · Posted

      Yeah, that's fine**. But the numbers you came up with are just wrong. Try it for yourself. Put in any voltage from the possible range and see what result you get. You get nonsense. ** When I say "fine", I mean, it's still shit. The very simple linear formula (slope & intercept) is shit for a sensor with a non-linear response. This is the curve, from your data above. Look at the CURVE! It's only really linear between about 30 and 90 °C. And if you used only that range to define a curve, it would be great. But you would go more and more wrong as you went to higher temps. And that is why the slope & intercept found when you use 50 and 150 as the end points is so bad halfway between those points. The real curve is a long way below the linear curve which just zips straight between the end points, like this one. You could probably use the same slope and a lower intercept, to move that straight line down, and spread the error out. But you would 5-10°C off in a lot of places. You'd need to say what temperature range you really wanted to be most right - say, 100 to 130, and plop the line closest to teh real curve in that region, which would make it quite wrong down at the lower temperatures. Let me just say that HPTuners are not being realistic in only allowing for a simple linear curve. 
    • Kinkstaah
      Mistakes were made, my R34 Story

      By Kinkstaah · Posted

      I feel I should re-iterate. The above picture is the only option available in the software and the blurb from HP Tuners I quoted earlier is the only way to add data to it and that's the description they offer as to how to figure it out. The only fields available is the blank box after (Input/ ) and the box right before = Output. Those are the only numbers that can be entered.
    • GTSBoy
      Mistakes were made, my R34 Story

      By GTSBoy · Posted

      No, your formula is arse backwards. Mine is totally different to yours, and is the one I said was bang on at 50 and 150. I'll put your data into Excel (actually it already is, chart it and fit a linear fit to it, aiming to make it evenly wrong across the whole span. But not now. Other things to do first.
×
×
  • Create New...