Marcin's spreadsheet is attached to this post (scroll down to bottom of post #1).

The math behind this is as follows (for those who want to know)...

Definitions

R0 = injector's rated flowrate measured at pressure P0

P0 = pressure at which the injector's rated flowrate R0 was measured (seeNotebelow)

FP = regulator "base"gaugepressure

MAP = manifoldabsolutepressure

BARO = barometricabsolutepressure = 101.3 kPa at sea level = 100 kPa approx. a little above sea level

MANVAC = manifold vacuum = BARO - MAP

gaugepressure =absolutepressure - BARO = value shown by pressure gauge

absolutepressure =gaugepressure + BARO

Pressuredifferenceacross an injector: this is the difference in thepressures above and below the injector.absolute

An unreferenced regulator has its pressure set constant; this pressure is FP (gauge) or FP + BARO (absolute).

A MAP-referenced regulator has a reference hose connected to the intake manifold,

so its pressure has MAP added to it; this pressure is FP + MAP (gauge) or FP + BARO + MAP (absolute);

with reference hose removed, this pressure becomes FP + BARO (guage) or FP + BARO + BARO (absolute).

The flowrate of an injector is directly proportional to the squareroot of the pressureacross the injectordifference(this is the Bernoulli pressure relationship).

Note on Injector Flowrate Measurement:

when R0 is measured on an injector flow bench, P0 is actually the pressuredifferenceacross the injector:

absolute pressure above injector = P0 + BARO; absolute pressure below injector = BARO; so then difference = P0.

Note regarding 1997-1998 Y-car:

The FPR isnotMAP-referenced (follow the reference hose to verify it sees atmosphere/BARO).

Unreferenced Regulator (e.g. 1998-2002 F-car, 1997+ Y-car)

Pressure difference (ofpressures) across injector = (FP + BARO) - (MAP) = FP + BARO - MAP = FP + MANVACabsolute

IFR = R0 * sqrt((FP + MANVAC) / P0) = varies/slopes with MANVAC

At the rail,pressure is FP + BARO, soabsolutepressure is FP.gauge

-->Directly measure FP at rail with engine running (FP should be constant).

The spreadsheet calculates this equation (Example 1, post #3).

MAP-Referenced Regulator (e.g. trucks)

Pressure difference (ofpressures) across injector = (FP + BARO + MAP) - (MAP) = FP + BAROabsolute

IFR = R0 * sqrt((FP + BARO) / P0) = constant/flat regardless of MANVAC

At the rail,absolutepressure is FP + BARO + MAP, sopressure is FP + MAP.gauge

Remove reference hose, regulator is now exposed to barometric pressure (so MAP = BARO),

and railpressure is FP + BARO + BARO, soabsolutepressure is FP + BARO.gauge

-->With reference hose removed, directly measure FP + BARO at rail with engine running.

The spreadsheet calculates this equation at MANVAC=0 if measured FP + BARO is entered (Example 2, post #3).

Units

Rail pressure is measured in psi, and MAP or MANVAC is measured in kPa.

You need to convert one to the units of the other before calculating IFR.

Convert psi to kPa by multiplying by (100/14.5).

14.5 psi = 100 kPa

If injectors are rated in lb/hr:

convert lb/hr to g/s by multiplying by 0.125998 (can round to 0.1260).

1 lb/hr = 0.1260 g/s

If injectors are rated in cc/min:

convert cc/min to g/min by first multiplying by density of gasoline (typically 0.73 g/cc), and then dividing by 60.

1 cc/min = 0.0122 g/s (depending on density of gasoline)