Go Fast

[cordes]

so as not to confuse people, 2 bars = 29.4 PSI. A 2 bar MAP sensors range is from -14.7 PSI (vacuum) -> +14.7 PSI (boost), for a total of 29.4 PSI.

Vac is not typically referenced in PSI, but in in. of hg.

A 2 bar map measures aboslute pressure to 2 bar. We only see 14.7 PSI of boost since we live at 14.7 PSI all the time, and therefore reference atmospheric pressure as 0 PSI. A three bar sensor will read 3 bar absolute pressure too. Once again you will only see 2 bar on your gauge since the 1 bar is the pressure around us.

[Clay]

Vac is not typically referenced in PSI, but in in. of hg.

not necessarily. Its all a function of how much vacuum you have. In our case, a car since the engines dont make lots of vacuum we use inches of mercury probably to get better resolution. A car running 20 in-hg has about 10 psi of vacuum. now on to the next part.......

A 2 bar map measures aboslute pressure to 2 bar. We only see 14.7 PSI of boost since we live at 14.7 PSI all the time, and therefore reference atmospheric pressure as 0 PSI. A three bar sensor will read 3 bar absolute pressure too. Once again you will only see 2 bar on your gauge since the 1 bar is the pressure around us.

This is true as well, it all depends on your point of reference. I usually reference things in PSIG (gage pressure) and so do the gauges we look at in the car. 20 in-hg (~10 psi) is really 4 PSIA (absolute).

clay

[Dave]

I always thought we live in 1 bar... 14.7psi. Added onto 14.7psi makes 2 bar. But in Manifold Absolute Pressure, it reads 14.7psi, not 29.4psi. So that's why I say a 3bar is good up to 29.7psi, b/c it will then cut out. Rob Pachner has this problem. He wants to run 30psi, but can't b/c it will cutout. He needs a 3.5bar MAP.

Thanks for cleaing up the clamp and diode part. I never used those.

[Frank]

sea level, we are at 1 bar, 1 atm, or 14.7psi. however indicated boost on a boost guage is referenced from atmospheric... 14.7psi. so if you are running "5psi" of boost, it is really 5psi above atmospheric. so yes a 2 bar map will do 29.4psi absolute, but when combined with the natural 14.7 atmospheric conditions, it will only be effective to the 14.7psi of indicated boost. 3bar is 44.1psi and 29.4psi respectively.


Frank

[Clay]

Yup, thats why we have PSIA and PSIG. A = absolute, so just sitting out on your desk it should read about 14.7 PSI, G = gage, so just sitting out on a desk it should read 0 PSI.

SO 14.7 PSIA = 0.0 PSIG

Its all about reference point.

[turbovanman²]

sea level, we are at 1 bar, 1 atm, or 14.7psi. however indicated boost on a boost guage is referenced from atmospheric... 14.7psi. so if you are running "5psi" of boost, it is really 5psi above atmospheric. so yes a 2 bar map will do 29.4psi absolute, but when combined with the natural 14.7 atmospheric conditions, it will only be effective to the 14.7psi of indicated boost. 3bar is 44.1psi and 29.4psi respectively.


Frank

[TrrboJeep]

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