Haltech E6X Manual DOS Version - Manual (Page 114)

E6X Manual
114
D.2 Fuel Requirement
If you can estimate the power output of a gasoline engine, you can make a reasonable guess at
the fuel flow requirement. The following is a guide to the quantity of fuel required:
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.
D.3 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, 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.
D.3 Injector Staging
Another way of increasing injector flow, without compromising good drivability and fuel
economy is to employ staged injection. Injector staging allows the use of primary and
secondary injectors and is usually only used on high boost turbo or supercharged engines. The
ECU will fire only the primary set of injectors until a preset load point, where the ECU will
control both primary and secondary injectors.
The turn on point for the secondary injectors depends on injector size and engine
performance, but will usually occur just after the pressure in the intake manifold of the engine
has reached atmospheric pressure. The staging point must occur before the primary injectors
have reached 100% duty cycle. Go to the highest speed range in the fuel map that the engine
is using, and make sure that the last bar for primary injection is not too high. If it is, you must
stage at a lower pressure.