Westers Garage - Technical Info

    .42 BSFC - Race Engine
    .47 BSFC - Hi Performance Engine
    .52 BSFC - Stock or with Light Modifications Engine
    .57 BSFC - Supercharged / Turbo Charged Engine

Most Injector burst pressures are at 125 PSI--and some injectors will hydraulic 'closed' at pressures above 50 PSI, so use extreme caution when choosing to use an FMU.

Pulse widths shorter than 0.8 mSec may cause idle or low speed driveability problems and exceed the dynamic range of the injector.

Injector Size	Horsepower Range
... 14 lb/hr	... up to 225
... 19 lb/hr	... 225-300
... 24 lb/hr	... 300-385
... 30 lb/hr	... 385-480
... 36 lb/hr	... 480-575
... 42 lb/hr	... 575-670
... 50 lb/hr	... 670-800

The above assumes the ability to change fuel rail line pressures.

Injector Flow Rate Conversion

CC/Min = LBS/HR x 9.71

LBS/HR = CC/min x 0.103

Injector tidbit

High Impedance Injectors -- Typically between 12-16 ohms. Used with ECM using saturation driver circuits. Low current--low heat, but slower response times for high RPM.

Low Impedance Injectors -- Typically between 1.2-4.0 ohms. Used with ECM circuits designed for "Peak and Hold". Current is normally 2-4A Peak with 0.5-1A hold. Peak current is generated to overcome the inertia of the closed pintle and once the pintle opens, the driver circuit cuts current to "hold" the pintle off its seat until the end of the metering event. High flow applications are most typical.

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Fuel Pump Flow Factors

Gallons Per Minute = LBS/HR / 369.8

Gallons Per Minute = HP / 740

Fuel Pressure

F1/F2 = (SQRT P1) / (SQRT P2)

F1 = Rated mass flow rate of injector at existing fuel pressure P1 in lbs/hour

F2 = New mass flow rate of injector at new fuel pressure setting P2 in lbs/hour

P1 = Existing Fuel Pressure Setting

P2= New Fuel Pressure Setting

P2 = (M2/M1)2 x P1

TBI applications

The fuel pump must keep the injectors fed with enough fuel flow to maintain as high as 20 PSI. The latter 454 TBI systems used higher pressures than the 9-13 GM Spec.

Multi-Port

The fuel pump must maintain at least 42 PSI at the fuel rail at 100% (static open) injector duty cycle. You'll find that above 50PSI MPFI fuel injectors may hydraulic closed ! FMU's are a very poor choice when supercharging. Racing applications can run 60, 70 and higher pressures. Choose appropriate injectors for your application and have them tested for performance at rated pressure.

FUEL PRESSURE AND VOLUME

The relationship between pressure and volume is inversely proportional. As pressure increases, volume decreases. You must understand this when designing a system for your vehicle. You cannot raise pressure and maintain the same volume. At WOT, a typical engine requires 0.5lbs of fuel per horsepower per hour to maintain 12.6 AFR. An engine rated at 400 HP will need 200 pounds or around 28.57 gallons of fuel per hour. Therefore, you should at least have a 30 gallon per hour fuel pump rating.

Fuel Line

You will need at least 3/8" fuel line for most street HP applications (depending on length). Most flow spec data is for water--fuel is of a lower specific gravity and flows faster with less friction, so don't let your plumber tell you what to do. Most OE fuel lines are 5/16" which did support up to 350HP for a 12-15 foot length of tubing with no flow problems.

A 110-140 GPH pump with 400HP Engine should have a minimum 3/8" or -8AN minimum fuel line size (Non return regulator) to 16 PSI.

A 250 GPH pump with 450HP Engine requires a minimum 1/2" or -8AN (Non return regulation) to 12 PSI.

When adding a return regulator, it's recommended to increase fuel line size another 1/8-1/4" I.D. Remember the relationship between pressure and volume. Larger injectors may require custom fuel rails to keep up with high demand.

How to test a fuel filter ? --More than 1.5 PSI differential across the inlet to outlet is a major restriction. Consider replacement BEFORE that time.

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Formula for Compression Ratio

CR = Cylinder Volume @ BDC / Cylinder volume @ TDC
CR = 0.7854 x bore x bore x stroke / combustion chamber volume + head gasket volume + Piston deck volume - Piston dome

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O2 Sensor Graph

wpe11.jpg (31558 bytes)

No matter what "they" tell you--you cannot use a narrowband O2 sensor for best performance tuning. The narrow band O2 is for catalytic converter operation only. That's what switching O2 sensors were designed for. The "high" volt accuracy (between 1.0-900mV) is not sensitive enough for air fuel ratio measurement. The switching of the O2 sensor properly metered excess O2 or excess HC to keep the burn going properly in the catalyst--yet maintaining an imperceptible surge which would normally result if this was attempted mechanically. Using the O2 narrowband for performance tuning is a mistake. Use wideband O2 sensing equipment , or even better--a 4 gas -- and watch the C0% !

Westers' Garage 218 Centre Street Box 159 Tilley, Alberta -- Canada T0J 3K0....We'll get YOU going FAST !!

1-403-377-CARS (2277) and 1-403-377-2270 (FAX) or EMAIL US

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