Injector Flows
The best guide to the flows of different injectors that we can find.
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We've found detailed specs for nearly 100 different injectors and summarised that information in a single comprehensive table. The information is rare and useful! So why would you want to know all of the stuff in the table anyway? It's damn important to know injector flow rates when you are sizing injectors for either a new system or an upgrade to an existing system. The flow rates shown in the table are those achieved at 100 per cent duty cycle, that is, with the injectors held fully open. In a well-sized system the injector duty cycle should not rise this high - a duty cycle maximum of about 90 per cent or so is about right.
For example, the Bosch 0 280 150 100 is listed as flowing a maximum of 185cc (cubic centimetres or millilitres) per minute when tested at a fuel pressure of 300kPa (~43psi).
So, how much power is this injector good for? That depends
on the air/fuel ratio that is used, but a good rule of thumb
is to divide this flow figure by 5 to get a hp capability. So,
185cc divided by 5 = 37hp maximum fuel flow with this
injector. If you want to be pedantic, it's the mass of the
fuel (not the volume) which is the critical factor. Assuming a
"normal" fuel density, the mass of the fuel in pounds per hour
can be worked out by multiplying the cc per minute figure by
10.2. For this Bosch injector, that gives a mass flow of 18.1
pounds/hour. Incidentally, if all of this mixing of units (pounds/hour,
cc/minute, hp, kPa and psi) gives you the horrors, don't worry
about using them all. Instead just pick the system you're
happiest with (eg cc/minute and hp) and stick to that.
The power ratings discussed above are for each
injector. This means that you need to multiply this rating by
the number of injectors that are to be used. So, if you were
using the Bosch 0 280 150 100 injectors in an eight cylinder
engine (with one injector per cylinder) the max power that the
injectors could deliver fuel for would be about 300hp. In addition to the variations in fuel flow from injector to
injector, you will also notice that the injector resistance
(ohms) varies. Injectors fall into two broad classes in terms
of their coil resistance - "low" and "high". Low resistance
injectors have 2-3 ohm coils, while high resistance injectors
are up around 14-16 ohms. If you are upgrading a car to larger
injectors, the new injectors should be of the same resistance
class as those being replaced. If you are fitting programmable
management, you must make sure that the ECU will be happy with
the coil resistance of the injectors that you have selected.
Note also that injectors vary substantially in their size
and shape. Some cars run side-feed injectors, while others are
end-feed O-ring types, where the fuel rail holds the injectors
in place. Still others use barbed hose fittings. Unless you
are prepared to do custom machining and fabrication work, you
need to be aware of the required injector size and shape
before you make the selection. Finally, injector wiring plugs
also vary; however, it's usually not much drama to wire in new
plugs - assuming that you can get them
