Professional Fuel Injector Pulsewidth Calculator

This calculator will generate pulsewidth values for specific rpms, from idle to peak speeds. The constants used are 160 CFM per 100 HP, and an 85% duty cycle for maximum injector pulsewidth. Injectors will go static at about a 92% duty cycle and should be sized for an 80% duty cycle to leave some "wiggle" room.

Beyond the 85% figure horsepower can actually drop as the pintles or discs in the injectors are essentially "floating", trying to open and close before they can complete each event. At this point the injectors actually put out less fuel until they are fully pulsed static and then the final output goes to 90% of their rated capacity. Injectors should not be pulsed beyond an 85% duty cycle.

Injectors are rated when shorted open @ 43.5 psi (3 Bar). The injectors will, when pulsed, only achieve 90% of this figure. Also calculated is the expected injector ccm flow at the selected rpm and load (KPa).

RB Racing only uses RC Engineering Fuel Injectors, either high or low impedance with ratings up to 1600cc/mim. We have known Russ Collins, who was inducted into the Motorcycle Hall of Fame, since 1974. Like the Don McLean song "Bye-Bye Miss American Pie"....motorcycle drag racing died and hasn't progressed technically since Russ Collins retired. Only one Buddy Holly...only one Russ Collins. The "Sorcerer", Russ's Nitromethane burning "V8" with two SOHC Hondas held the Top Fuel record for 12 years.

Doubles, triples, V8's, Hilborn Injection, Nitro, Superchargers, rear facing zoomies, Cobra Motors, Golden Rods, Sidewinders, Webers, Strokers, Flowbenches, Dynos, 4-1's, rotational firing collectors, magnetos, belt drives, slipper clutches, data acquistion, white leathers, professional presentation, feathered hats and a victory cigar.

If you ever wonder where Terry Vance and Byron Hines got their start....Well, everyone needs someone to lead the way. Anyone can copy.

Injector Wet Flowbench

At RB Racing we wet flow our RSR Fuel Injection Systems to see the actual horsepower outputs. We can test specific fuel pumps, regulators, injectors and set fuel pressures to meet the particular requirement. We also simulate temperture changes in the engine as well as the inlet air temperatues. Variables on our RSR Wet Flowbench are Air Temp, Engine Temp, TPS, O2, Manifold Pressure, RPM, start functions, battery voltage, fuel pump size ( 300, 400, 600, 1000 hp), and fuel pressure. We can visually monitor horsepower output and bypass fuel. All RSR ECU's are tested on the flowbench prior to shipment.

Volumetric efficiencies are related to inlet tract design and inertia considerations. At idle your V.E. might be as low as 15% to 20% whereas at higher and peak rpms in some systems V.E. can be 100% or greater. Typically full power or higher rpms are calculated @ 85% V.E. as an average. V.E. usually rises quickly off of idle as inertial filling takes place. If the inlet system is too restrictive then V.E.'s can fall off as the rpms pass their most efficient flow.

Mach Indexes in the inlet system need to be considered in engine design.

Professional Fuel Injector Calculator (Idle & Peak Values)

Engine Displacement (CID):
Idle Target RPM:
Idle RPM
Peak RPM: Your rev limit may occur before the peak value.
Peak RPM
Volumetric Efficiency at Idle is typically 10% to 15%:
Number of injectors in the System:
Brake Specific Fuel Consumption (.5 for 2 Valve, .45 or less for 4 valve):
Idle in Inches of Mercury (In Hg.)

If Idle in Kilopascals (kpa): Then kpa / 3.3864 = In Hg

" Hg
Expected Peak Horsepower
Peak Hp
Millisecond (Ms) Injector minimum open time ( 1 to 1.25):
Your Installed Injector size (lb/hr):
Number of injections per cycle (batch 2, sequential 1):
How many strokes per cycle (four stroke = 4):
Injector Size @ 80% recommended duty cycle (lb/hr):
Max Hp with recommended injectors @ 85% duty cycle:
Peak Hp
Max Pulse Width Permitted @85% duty at peak rpm: (Ms):
Ms Peak
Max HP with Your Installed Injectors @ 85% duty:
Max Hp
Idle Millisecond Pulsewidth: Installed Injectors
Ms Idle
Projected cc's per minute: Installed Injectors, per injector at idle:
cc's / Inj.