"vacuum" kpa different than kPa?

[Wilde Racing]

I never paid much attention to the IFR tables until the other day, why is the table in vacuum kpa?
What the hell is "vacuum kPa"?

I though kPa was an absolute measurement??

[Trever1T]

(lmfao) Hey buddy!

yes, why is the IFR on returnless fuel systems scaled higher as Kpa (vacum) increases?

[5_Liter_Eater]

kPa is just a unit of pressure measurement. The values you see in the IFR table are kPa of vacuum (just negative pressure). So 0 kPa is actually WOT and the increasing numbers are increasing manifold vacuum. The injectors flow more when they're under vacuum. The manifold vacuum literally helps suck out the fuel. It works the opposite in an FI application, the inectors flow less when they have to work against the manifold pressure but the table does not account for that.

[Trever1T]

Thanks!

[Dozer]

kPa is just a unit of pressure measurement. The values you see in the IFR table are kPa of vacuum (just negative pressure). So 0 kPa is actually WOT and the increasing numbers are increasing manifold vacuum. The injectors flow more when they're under vacuum. The manifold vacuum literally helps suck out the fuel. It works the opposite in an FI application, the inectors flow less when they have to work against the manifold pressure but the table does not account for that.

[Wilde Racing]

kPa is just a unit of pressure measurement. The values you see in the IFR table are kPa of vacuum (just negative pressure). So 0 kPa is actually WOT and the increasing numbers are increasing manifold vacuum. The injectors flow more when they're under vacuum. The manifold vacuum literally helps suck out the fuel. It works the opposite in an FI application, the inectors flow less when they have to work against the manifold pressure but the table does not account for that.

I understand that, but I want to know what the hell kPa "VACUUM" is, kPa is kPa.

[Dozer]

Thats why we run boost ref FPR that increase 1:1 to account for the increase of manifold pressure from boost. (edit: that was strange it split the quote from my post????)

[Dozer]

I understand that, but I want to know what the hell kPa "VACUUM" is, kPa is kPa.

This is all i could find. Low vacuum is often measured in inches of mercury (inHg), millimeters of mercury (mmHg) or kilopascals (kPa) below atmospheric pressure. "Below atmospheric" means that the absolute pressure is equal to the current atmospheric pressure (e.g. 29.92 inHg) minus the vacuum pressure in the same units. Thus a vacuum of 26 inHg is equivalent to an absolute pressure of 4 inHg (29.92 inHg - 26 inHg).

[EC_Tune]

I understand that, but I want to know what the hell kPa "VACUUM" is, kPa is kPa.

You can actually log the Vacuum Kpa PID if you wish. KiloPascal's are simply a measurement of pressure whether that be an absolute value (MAP) or a relative value (Vacuum). HTH

[Wilde Racing]

You can actually log the Vacuum Kpa PID if you wish. KiloPascal's are simply a measurement of pressure whether that be an absolute value (MAP) or a relative value (Vacuum). HTH

O.K maybe a better question is why is it relative.. what, never mind I guess you would want it relative.

I just got confused with "kpa" always equaling absolute. but I guess PSI can be both, so why the hell can't kPa...lol

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