New Online Jetting Calculator: Pro Calc

Pro Calc is now available for your internet ready device: iphone, lap top computer, desk top computer, or other web ready device. It will calculate jetting and nozzles in mechanical fuel injection engines in the pits or staging lanes for weather or tuning adjustments.

FOR EXAMPLE: We used Pro-calc to set up nozzles and jetting for 5 different fuel combinations, all confirmed in only 15 drag race test runs. That was an average of three runs per combination to determine nozzles and jetting baselines for full quarter mile drag race passes with good spark plug color, even burning on all cylinders, no bog, no misfiring, and great power. All of the jetting was determined prior to the first test run of each combination with PRO-CALC using information recommended in our books for air to fuel ratios, fuel system pressures, nozzle fuel distributions, and hat to port fuel split percentages discussed in our books. Guess what, technology works.

PRO-CALC NOZZLE & JETTING ANALYSIS CAPABILITIES

  • PRO-CALC is for both normally aspirated & supercharged engines.
  • PRO-CALC calculates nozzles and jetting for mechanical fuel injection for engines from 1 to 8 cylinders.
  • PRO-CALC can calculate up to 4 nozzles per cylinder.
  • PRO-CALC can determine jetting with or without a high speed bypass.
  • PRO-CALC provides a record of your baseline. Then it determines jetting changes for different air densities, altitudes, and tune-ups.
  • Three baselines can be set up. For example, if you are an engine builder, you could have one baseline for normally aspirated engines, another for supercharged engines, and use the third baseline record to determine specials or the one you are currently building.
  • PRO-CALC determines the air to fuel ratio (AFR). We used a prototype of PRO-CALC to determine AFRs for over 400 runs that we made, and for hundreds of other competitors in several forms or racing with mechanical fuel injection.
  • PRO-CALC can provide information to determine fuel to the engine.
  • PRO-CALC determines the fuel pressure.
  • PRO-CALC can be calibrated to a fuel pressure reading from a flow bench, dynamometer, or on-board instrumentation value.

TUNING NORMALLY ASPIRATED ENGINES WITH PRO-CALC
The tuner can adjust nozzles and jetting in a normally aspirated racing engine to control:

  • air to fuel ratio for peak torque
  • air to fuel ratio for peak horsepower
  • air to fuel ratio with high speed bypass closed
  • air to fuel ratio with high speed bypass open
  • adequate fuel pressure
  • fuel split between the up-nozzles and down-nozzles in double nozzle setups
  • nozzle or main bypass changes for changes in weather or location
  • high speed bypass jetting size
  • high speed bypass poppet or regulator pressure setting to open at a specific engine speed
  • nozzle or main bypass changes to accurately lean out an engine for maximum power
  • air to fuel ratio profiling for ram air effects with increase in speed
  • air to fuel ratio profiling for ram air effects for gear changes
  • air to fuel ratio profiling for boat racing long term straight-aways against and with head winds
  • fine tuning the high speed size for seamless transition from peak torque to peak horsepower flat lining
  • jetting changes at an event for changes in temperature, pressure, and humidity from the morning to the evening
  • jetting changes for different events for changes in temperature, pressure, and humidity from day to day
  • jetting changes for different locations from altitude or regional effects in weather
  • in US racing locations, combine PRO-CALC with http://airdensityonline.com air density predictions for future jetting changes such as in preparation for a long term sprint race events or boat racing marathons.

TUNING SUPERCHARGED ENGINES WITH PRO-CALC
For a supercharged engine, the tuner can do all the above plus:

  • changes in hat vs port nozzle fuel split for the best tradeoff between blower lubrication, fuel distribution, and intake manifold temperature; for example, our most recent setup puts about 45% of the fuel in the hat and the remainder in the manifold. This combination produces our manifold temperature goal of about 140 deg F. Without port nozzles with all the fuel in the hat above the blower, our manifold temperature was less than 100 deg F. That was considered too cool for this low compression setup. The engine was not very responsive.
  • changes in hat vs port nozzles for a fuel split goal to control boost
  • changes in hat vs port nozzles to reduce fuel standoff and a tornado effect at the top of the blower inlet limiting the air intake and the power
  • nozzle or main bypass changes for changes in blower overdrive
  • nozzle or main bypass changes for changes in blower efficiency such as when blower seals loosen from repeated runs. We rate our resealed blowers at 5% blower efficiency above what we rate a blower with around 50 runs without new rotor seals. That adjustment in the baseline provides a proper influence to the jetting size calculations that are necessary for other tuning needs such as changes to weather or altitudes.
  • nozzle or main bypass changes for changes in blower size
  • port nozzle changes for fuel distribution tuning
  • air to fuel ratio profiling to bring a high speed in or out for gear changes
  • air to fuel ratio profiling for boost increases due to ram air from speed increases
  • high speed jet fine tuning for blower efficiency changes at high speed.

PRO-CALC EXAMPLES
Note the following unblown engine example:

  • normally aspirated 410 ci small block with up-nozzles (manifold) &
    down-nozzles (cylinder head ports)
  • air density = 100%
  • fuel pump = 4 GPM at 8,000 engine RPM (1/2 pump speed)
  • VE @ torque peak = 100% (see note 1 below)
  • air to fuel ratio at torque peak = 5 to 1
  • VE at horsepower peak = 80% (see note 2 below)
  • air to fuel ratio at horsepower peak = 5.4 to 1
  • Pro-calc determined up-nozzles = 8 x 0.022 inch dia.
  • Pro-calc determined down-nozzles = 8 x 0.022 inch dia.
  • Pro-calc determined main bypass = 0.080 inches dia.
  • Pro-calc determined high speed = 0.070 inches dia.
  • Pro-calc determined fuel pressure @ 8,000 RPM with high speed closed = 97 psi
  • Pro-calc determined high speed poppet pressure
    to open high speed at 5,500 RPM = 46 psi
  • Pro-calc determined fuel pressure @ 8,000 RPM with high speed open = 54 psi.

The above example is typical of a mechanical fuel injection system set up for “flat lining” a fuel curve. Flat lining is explained further in our jetting manuals for
normally aspirated small blocks or normally aspirated big blocks.

Note 1: Brake specific fuel consumption of 1.0 pounds per HP per hour at torque peak (ref. 5HPM, p. 149) yields 444 HP from this engine at torque peak of 5,500 RPM, using the math from FIRS, p. 168. A horsepower level of 444 at 5,500 RPM computes to a torque value as follows:

torque = HP x 5252 / RPM = 444 x 5252 / 5500 = 424 foot-pounds

Note 2: Brake specific fuel consumption of 1.05 pounds per HP per hour at horsepower peak (ref. 5HPM, p. 149) yields 611 HP at 8,000 RPM from this engine, using the simple calculation from FIRS, p. 168.

FINE TUNING JETTING: Accurate & repeatable fine tuning is illustrated for this setup in the following tuning changes:

(1) To lean the engine a small amount to 5.5 to 1 (from 5.4 to 1)
in fine tuning for more power:

  • Pro-calc determined main bypass = 0.082 inches dia
    (from 0.080 determined in the baseline)

(2) To richen the engine a small amount to 5.3 to 1 (from 5.4 to 1)
in fine tuning for more power:

  • Pro-calc determined main bypass = 0.078 inches dia
    (from the previous 0.080 & 0.082 determinations)
  • Footnote: Assume typical spare jet sizes in 0.005″ increments (0.085, 0.080 in the engine, 0.075, etc.). If you put a 0.075 in the main bypass instead of the 0.078 that is determined by PRO-CALC, you would be changing the air to fuel ratio to 5.18 to 1 according to PRO-CALC. That would be a coarse enrichment and likely a loss in power. Your search for more power from enrichment would be a failure because the change is too big.

JETTING FOR WEATHER OR ALTITUDE: Examples that maintain the same air to fuel ratio of 5.4 to 1 for different air densities:

  • for air density = 95%
  • Pro-calc determined main bypass = 0.085 inches dia
    (from the previous 0.078, 0.080, & 0.082 determinations)
  • for air density = 90%
  • Pro-calc determined main bypass = 0.092 inches dia
    (from the previous 0.078, 0.080, 0.082, & 0.085 determinations)

Pro-calc can determine nozzles & jetting for

  1. small changes to the tune-up for enrichment or lean out
  2. track or course altitude changes
  3. weather changes
  4. nozzle fuel split changes and many others.

HOLDING CONSTANTS WITHIN FUEL SYSTEM
With Pro-calc, the tuner can choose to hold any of the following:

  • system pressure constant
  • or air to fuel ratio constant
  • or any combination of nozzles and jetting constant (such as all port nozzles held the same and varying only manifold nozzles if a nozzle change is needed).

SAVE ON COST OF SPARES
Pro-calc can be used to best fit your available inventory of nozzles and jetting to subsequent tuning needs. For example, PRO-CALC was used in a recent test to predetermine nozzles and jetting before a dynamometer test. Then the fuel injection hardware was made available to test all intended combinations on the dynamometer. The dynamometer test was then done to thoroughly evaluate the fuel system with the appropriate nozzle and jetting changes possible as all the parts were already identified ahead of time and made available for the test.

SUMMARY
Using PRO-CALC and the technical information from FIRS & 5HPM, the predetermination is illustrated of an engine horsepower & torque goal with the required jetting. We are using PRO-CALC in a similar manner for our supercharged engine with great success. I would not want to ever race without it.

Posted on February 28, 2011 by Jennifer

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