Injector duty cycles

[Mazda Ebrahimi]

Roger Feingold wrote:
> 
> I'm working on sizing injectors for a '88 2.8 V6 MPFI. Does anyone have
> experience with the max duty cycle when at WOT and redline? My computations
> show stock 16 lb/hr injectors will be maxed out by the time the engine hits
> 5000 rpm and 12.6:1 A/F.
> Also, has anyone correlated the O2 sensor voltage vs. A/F ratio?
> 
> Thanks,
> 
> Roger.I had always been told for proper injector sizing, you don't want to exceed 80% duty 
cycle at WOT, max RPM.  But someone on the mailing list said their injectors on a 3.8L 
turbo GN go upto 99% at WOT.

If you calculated your fuel reuiqrement based RPM and displacement, did you consider 
maximum Volumetric Efficiency for that engine is less than 100%?

I think that engine makes about 145 HP at 4600 RPM (these numbers may be off a little, 
but lets use them for sake of argument).  at 145 HP, the engine should be consuming 
approximately 15 lbs of air per minute  (I got 15 by dividing 145/10 and rounding up.  
It's an approximation) (or 900 lb/hr).  Given 12.6 A/F, you need 71.4 lb/hr of fuel, 
which divided by six cylinders results in 12 lb/hr injectors.  Given you have 16 lb/hr 
injectors, they shouldn't see much more that 75% at normal conditions (maybe higher when 
ambient air temp is cooler), which comply with the 80% rule of thumb.  Do you know what 
the actual duty cycle for those injectors is?

Best Regards, Mazda

Best Regards, Mazda