CanaryGT said:
It makes more sense except why do you put in a higher multiplier for a forced induction car as opposed to a NA??
It has to do with something called
Brake Specific Fuel Consumption. This is basically a ratio of fuel consumption to engine output. Basically, a naturally aspirated motor can make the same power with less fuel than a forced induction (turbo, blown) motor of the same horsepower output. In the formula above, you'll notice that Saleen put up a .5 BSFC for N/A, and .6 for blown. These are decent round number figures that can be used when calculating fuel injector requirements for an engine.
It is always better to "over-inject" a motor (within reason) since you can just limit the pulsewidth of the injector via the tune in the ECU. Very large injectors (e.g. 160 lb/hr) can sometimes be a bit difficult to tune for idle/drivability due to the very large amount of fuel dispersed in a very short time.
However, although 42s may be a little larger than necessary (not by much) for you application, it will easily be compensated for by the tune, and will allow you some room to grow if necessary.
Oh, and you never want to run an injector past 85% of its maximum duty cycle. That is, past the maximum amount of time it can stay open when spraying fuel into the intake manifold.
Hope that helps.
Paul.