What is the vacuum/psi of 1grfe? - Toyota FJ Cruiser Forum
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post #1 of 10 (permalink) Old 07-15-2013, 01:51 AM Thread Starter
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What is the vacuum/psi of 1grfe?

Does anyone know the stock vacuum or PSI for a supercharged or non-charged 1grfe engine? From what I understand, correct me if I'm wrong, the intake manifold pressure is measured in HG vacuum unless a supercharger is installed then it is measured in PSI (assuming the charger boost is greater than vacuum).. I'm trying to find the base, I know it varies by elevation/BP/etc, vacuum or PSI for either a charged or non-charged 1grfe engine. Thanks, Bob.
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post #2 of 10 (permalink) Old 07-15-2013, 06:16 AM
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Re: What is the vacuum/psi of 1grfe?

Thought the TRD unit advertises around 5-6 PSI, but that obviously varies quite a bit depending on your elevation.



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post #3 of 10 (permalink) Old 07-16-2013, 12:12 AM Thread Starter
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Re: What is the vacuum/psi of 1grfe?

Is that net PSI? Or boost? If the baseline is vacuum -3 & you add a supercharger that boosts 6 psi that would be a net 3 PSI correct? Or am I way off on my understanding?
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post #4 of 10 (permalink) Old 07-16-2013, 12:20 AM Thread Starter
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Re: What is the vacuum/psi of 1grfe?

I'm looking into getting a water/meth injection kit & am trying to decide what to get. I want a boost controller that uses vacuum/psi not EFI. In order to get the right controller I need to know the vacuum/psi of a charged 1grfe. Tried searching for a chart or graph or any info for manifold pressure over an rpm curve but haven't had any luck.
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post #5 of 10 (permalink) Old 07-16-2013, 04:10 AM
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Re: What is the vacuum/psi of 1grfe?

6psi off the supercharger, that's approximately what the pressure goes to, not 6psi net.



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post #6 of 10 (permalink) Old 07-16-2013, 09:33 AM
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Re: What is the vacuum/psi of 1grfe?

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3/325 previously said: View Post
I'm looking into getting a water/meth injection kit & am trying to decide what to get. I want a boost controller that uses vacuum/psi not EFI. In order to get the right controller I need to know the vacuum/psi of a charged 1grfe. Tried searching for a chart or graph or any info for manifold pressure over an rpm curve but haven't had any luck.
EFI = Electronic Fuel Injection, no boost controller i've ever seen operates on fuel pressure (but I haven't followed the boost game closely for a few years now, so there could be some crazy new contraption out there)


All boost controllers are pressure based. Are you trying to say you want a manual (usually spring and ball valve based and controls vacuum/pressure source based on another vacuum/pressure input) boost controller over an electronic (measures pressure and sends an electronic signal somewhere) one?
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post #7 of 10 (permalink) Old 07-16-2013, 01:57 PM
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Re: What is the vacuum/psi of 1grfe?

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3/325 previously said: View Post
Does anyone know the stock vacuum or PSI for a supercharged or non-charged 1grfe engine? From what I understand, correct me if I'm wrong, the intake manifold pressure is measured in HG vacuum unless a supercharger is installed then it is measured in PSI (assuming the charger boost is greater than vacuum).. I'm trying to find the base, I know it varies by elevation/BP/etc, vacuum or PSI for either a charged or non-charged 1grfe engine. Thanks, Bob.

Manifold pressure at idle should be the same for either vehicle, with or with out supercharger... It should also be the same under any condition where the supercharger is not building boost, IE cruising or low throttle ...

When you would not be at 0 in hg in a NA car, the supercharger should have it's bypass valve open, and the manifold pressure should be identical on the same engine with or with out a supercharger. When you open the throttle and manifold pressure goes to 0psi/0inhg the bypass valve closes and you start building boost.

Most map sensors are self-normalizing, so your vacuum at any elevation, per the gauge, should read the same. It resets 0 to actual atmosphere. Which is why an aftermarket electronic gauge like an auto meter needs voltage that survives crank, because if it resets during crank it will 0 with slight vacuum. A mechanical gauge will read differently at altitude.

Boost gauges generally show in hg of vacuum on the left, 0 in the middle and then PSI of boost on the right.
The factory computer probably reads it in Kpa. ~100 Kpa = ~14.7 psi, or atmosphere pressure at sea level , 0 kpa is a perfect vacuum... 200 KPA would be ~14.7 psi of boost. It's really like 101.3 kpa for atmosphere or something like that, but you get the idea.

The TRD supercharger is a positive displacement pump, so elevation is largely irrelevant, delta p should be the same no matter the elevation. If it's "rated" at 6 psi, then at what ever engine RPM they are rating it at the outlet pressure should be about 6 psi higher than the inlet pressure.

Last edited by f0rcedinducti0n; 07-16-2013 at 02:04 PM.
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post #8 of 10 (permalink) Old 07-16-2013, 08:16 PM Thread Starter
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Re: What is the vacuum/psi of 1grfe?

Thanks for the info Forcedinduction! That was what I needed to know.

iqdchkn, there are boost controllers out there now that apply boost based upon the EFI input. They increase the boost as the the EFI increases fuel.
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post #9 of 10 (permalink) Old 07-16-2013, 08:24 PM
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Re: What is the vacuum/psi of 1grfe?

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Thanks for the info Forcedinduction! That was what I needed to know.

iqdchkn, there are boost controllers out there now that apply boost based upon the EFI input. They increase the boost as the the EFI increases fuel.
Do you have a link to such a device because that sounds wrong?

An engine needs more fuel pressure based on boost pressure not the other way around. A typical engine will have about 40psi of fuel pressure to operate under vacuum. Then as boost increases the amount of air pressure the fuel pressure has to rise to compensate and over come that added pressure. It doesn't make sense for an engine developer to increase fuel pressure before there is boost pressure because it's not needed and increasing fuel pressure reduces volume. So adding fuel pressure is a necessary evil of boosting and engine because it has to be done to get the fuel in there, not because there is really any other benefit.
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post #10 of 10 (permalink) Old 09-16-2014, 01:27 AM
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What's wrong, ScanGaugeII can't read Manifold Absolute Pressure or Boost. Is there sensor at all in 2007 FJ Cruiser?
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