So today I was monitoring my car data and logging everything, when I was driving on the highway going +60mph and on ~2500RPM, my intake manifold pressure read +10Psi. I read it's usually near 5Psi. On idle, mine is around 5Psi.

Is this normal?

  • Is that a gauge or absolute reading? Makes a big difference. What is the car? Turbo? Supercharged?
    – Solar Mike
    Sep 28, 2019 at 21:13
  • The intake manifold pressure is not speed dependent but rather load dependent. For instance 60 mph going downhill is likely to produce a LOW manifold pressure (i.e. a vacuum) while 60 mph uphill will make for a relatively high pressure. A 5 psi reading at idle, however, sounds about right. Are you diagnosing a specific problem or just curious?
    – jwh20
    Sep 28, 2019 at 21:38
  • @jwh20 - It really depends on the vehicle ... most stock vehicles I've seen do not produce positive pressure (either turbo or supercharged) until under load, and never at idle. 5psi at idle seems very high and 10psi under load even higher, especially driving down the highway at 2500rpm. Most stock vehicles don't produce more than 7-8psi, and many under that. Sep 28, 2019 at 22:14
  • @Pᴀᴜʟsᴛᴇʀ2 It's going to be +5 psi relative to +14 (or so) psi ambient. Which makes 5 psi a vacuum which is what it should be. If the intake was actually at +5 psi (i.e. about 19 psi) that would be an impossible reading even with a turbo or supercharger since they will not create 5 psi of boost at idle.
    – jwh20
    Sep 29, 2019 at 1:20
  • 1
    @Everyone if it is not pressure induction then it is correct.
    – Solar Mike
    Sep 29, 2019 at 5:37


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