At 11:59 PM 11/22/99 -0500, you wrote:
>I've now had my stock 19lb injectors in for a week now, after swapping from
>the 24lb and the results are in:
>1. Decreased throttle response, a little dead spot (okay, a big dead spot)
>when I nail the gas at a low rpms in a low (2nd) gear. The 24's felt a
>little better, but idled very rich. I would still have them in if I did not
>have a bad injector.
>2. No decrease in overall power detected.
>3. Fuel economy up to 15 mpg from 12 mpg.
>NOTE: I did have the stock 318 computer with the 24lb injectors, when I
>later swapped the the Mopar 93 5.9 HP-SBEC, the 24lb injectors seemed to run
>way too rich. I later found that the O2 sensor was unplugged, which may have
>influence the results. I just helped a guy from Chicago install a 5.9 in his
>94 Dakota 4x4, his is running fine with a stock 5.9 engine, stock injectors,
>and a stock 94 5.2 computer. Go figure!
There is a formula that you can use to determine proper injector size for the
horsepower output of the engine. First is an accurate estimate of the
engine's
hp. Second is an estimate of the brake specific fuel consumption (BSFC which
is expressed in pounds per hp per hour). This is found by dividing the pounds
of fuel per hour used by the uncorrected hp output. This number will range
from 0.40 to 0.60 for gasoline-burning engines. As an engine becomes more
efficient in converting fuel into hp, the BSFC number will decrease. A
realistic
number for an average stree performance engine is 0.50.
The formula looks like this:
injector flow rate = (engine hp x BSFC)/no. of injectors x 0.8
The 0.8 figure is an 80% duty-cycle reduction of the total output of the
injector
since all injectors are rated at a 100% duty cycle. 80% is used by most
car manufacturers.
Example: assume engine output is 500 hp,
injector flow rate = (500 x 0.50)/(8 x 0.8) = 39 lb/hr
Therefore, the closest injector to this size is a 38 lb/hr. If the 500 hp
was a conservative estimate, you could move down to 34 lb/hr, or move up
if more hp is anticipated in the future. To put things into perspective,
a 96 lb/hr injector would adequately feed more than 1200 hp.
Whenever larger injectors are installed, the engine calibration must be
changed
to match the pulse width issued to the engine's needs. A 19 lb/hr injector
size at 43.5 psi with a fuel pressure of 50 (close to ours) will have a
flow capacity
of 20.37 while a 24 lb/hr injector will have a flow capacit of 25.73.
Hope this helps.
Bob. Southern Ontario, Canada.
'97 Dakota CC Sport, FR, 5.2L, 3.55 SG, auto.
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