Haltech E8 - Manual (Page 150)

Haltech E11/E8 Instruction Manual
Fuel Systems
The best EFI installation will yield poor results if the fuel system does not meet the demands of the
engine. Insufficient fuel flow can lead to engine lean out and detonation that 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 i.e. that the 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.
Flow Estimation
If you can estimate the power output of a gasoline engine, you can make a reasonable guess at the fuel
flow requirement. A simple rule of thumb, thus, may be expressed in metric or imperial units.
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.
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. Make 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,
and that 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 flow is not in direct proportion to
fuel pressure. Increasing fuel pressure will increase injector dead time and reduce the flow rate of the
pump.
Fuel Pump Capacity
You should ensure that your fuel pump is capable of supplying sufficient fuel to feed the engine at
Page: 150 Copyright © Haltech 2008
WARNING
Fuel is dangerous. Beware of flames, cigarettes, electrical sparks, etc.
Whenever you are working with exposed fuel, make sure you are working
in a well-ventilated environment.