Haltech F10 - Manual (Page 94)

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APPENDIX C FUEL SYSTEMS & STAGING
Insufficient fuel flow can lead to lean fuel mixtures resulting in high chamber temperatures
and detonation which could cause serious damage. For the safety of your engine, we urge you
to check your fuel system's capacity and ensure that there will be sufficient supply at all
times. A fuel pressure meter should be used during testing and tuning to ensure that fuel
pressure does not fall out of regulation, that is, the fuel pressure does not drop or oscillate.
This appendix offers guidelines to testing your fuel system and suggests some solutions if
there are supply problems. If you find you need to modify your fuel system and are unsure
what to do, contact a Haltech dealer for advice.
WARN ING:
FUEL IS DANGEROUS. BEWARE OF FLAMES, CIGARETTES,
ELECTRICAL SPARKS, ETC.
C.1 Fuel Requirement
If you can estimate the power output of a gasoline engine, you can make a reasonable guess at
the fuel flow requirement. A good estimate may be expressed in metric or imperial units as
follows:
Note: Every 100 hp needs around 50 lb/hr (8.0 US gal/hr) of fuel
(6.6 Imp gal/hr)
Every 100 kW needs around 670 cc/min (40 L/hr) of fuel
This assumes a brake specific fuel consumption of 0.50. The actual fuel flow necessary by
injectors and pump are likely to exceed a figure derived this way. This is due to the
overheads in injector dead time and pumping return fuel to maintain regulation.
C.2 Injector Flow Capacity
If you have purchased second hand injectors, or have removed the current injectors while
doing work on the engine, we strongly recommend that you clean and flow test them. If you
have bought new injectors, it is worth flow testing them anyway if you do not know their flow
rate. M ake sure that you test the injectors at the fuel pressure that your regulator is operating.
Your total injector flow capability is given by the sum of the injector flow rates. Injector flow
rates are usually specified in either cc/min or lb/hr. Check that you have enough injector flow
to match the estimated power output comfortably. Keep in mind that you do not want to
exceed 85% duty cycle injection “on” time. At high rpm, injector dead time can consume a
significant amount of available injection time.
If you find that your injector flow is insufficient, you can change to larger injectors, add extra
injectors, or increase fuel pressure. Raising fuel pressure to increase injector flow rate is not
recommended if the desired flow is more than 20% than the system currently achieves. Fuel