Barry Gardner wrote:
Paul,
I have some information to share about the question of Mazda fuel
injectors.
The reason that there are few / no substitutes for Mazda fuel
injectors is that the are so cotton-pickin' big. The reason for
their size is there are fewer of them to spray the fuel. A high
horsepower piston engine will typically be a V-8, so
manufacturers can split the fuel spray load over 8 injectors. Not
so with the two rotor Mazda. In fact, if you read hot-rodders
discussion of how to hop up their injection systems, you will
frequently see them look to the Mazda injectors as the biggest
and baddest.
I attached an Excel spreadsheet that lists the spray volume of a
whole series of injectors. For those people who don't have Excel
or who wish to view the table on-line, it can be found at:
http://www.wolfems.com.au/injector_flow_rates.htm
The four injectors for the naturally aspirated Mazda 6-port 13Bs
are rated at 460 cc/min (100% duty cycle). The four injectors for
the 4-port Turbo II's are rated at 550 cc/min. People who desire
to increase the horsepower on Mazda rotaries frequently go to the
680 cc/min injectors that could be found on an earlier Mazda (I
think the 86 GSL-SEs had just two of these big boys to run the
whole show). The 720 cc/min ones that Ray Lockhead sells at
Shaneracing are even more exotic, coming from a Cosmo I think.
If you compare those capacities to the ones listed on the table,
you'll find that they are off the chart on the large size.
I read somebody's book on fuel injection (which I can't find at
the moment, or I'd quote the source; it might have been Modern
Engine Tuning by A. Graham Bell) and supposedly injectors bigger
than even these are hard to control and close at the low end. You
can't get the really big ones to idle. So you need to stage the
really big ones with smaller ones that can be controlled better
at the bottom end.
If you do the math, the four Turbo II 550 cc/min injectors are
big enough for most of the horsepower requirements this list is
looking for. The attached table uses 10.2 as the conversion
factor between cc/min and lbs/hr but I've used a 10.5 factor
here, from other sources.
550 cc/min / 10.5 conversion factor = 52.4 lbs/hour Stock turbo
680 cc/min / 10.5 conversion factor = 64.7 lbs/hour 86 GSL-SE
720 cc/min / 10.5 conversion factor = 68.6 lbs/hour from Ray
@Shane Racing
Duty cycle/HP support computation
stock turbo fuel injection setup
4 injectors x 52.4 lbs/hr = 209.6 lbs/hr
209.6 lbs/hr x .80 duty cycle = 167.7 lbs/hr
167.7 lbs/hr /.55 BSFC = 305 HP max
167.7 lbs/hr / 6 lbs/gal = 27.9 gals/hr
The list should remember that Mazda switched from lo-impedence to
hi-impedence versions of the injectors during the 86-88 to 89-91
versions of the car. I have no information about the 13-BREW
stock injectors.
Hope this helps somebody.
Barry Gardner
Wheaton, IL
It certainly does Barry. Good work. Thanks.
This is why I advocate going to six or more injectors when designing your own
manifold.
Perhaps we could also take an engineering look at the throttle body injectors.
Paul Lamar
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