We are seeing racers from time to time who open and close a fuel injection bypass to pulse the fuel curve. According to our numerical analysis of air to fuel ratios from our ProCalc fuel injection calculator, bypass jet sizes much bigger than 0.050 inches are too large if they are shut off or on during a power run. The change in air to fuel ratio for most fuels is too great. Either the engine is too rich before it opens or too lean before it closes.
Smaller bypass jet sizes are recommended. In our engine testing in power levels between 1,000 and 2,000 HP, we found a high speed bypass jet size of 0.040 inches diameter to cause an air to fuel ratio change of about 0.15 points. That air to fuel ratio difference kept the engine within the good power making range whether the high speed bypass was open or closed. It provided the ability to launch our engine with a bit of extra fuel for response. With a high speed bypass pathway located after the barrel valve, it also provided an extra safety factor of fuel if the throttle was lifted for traction loss or drifting. Then, when the throttle was hammered back on, the engine came from a rich state before leaning down to the ‘best power’ air to fuel ratio. This method reduced the chances of backfiring from air surges caused by throttle manipulation.
GRAPHIC ILLUSTRATION ABOUT PULSING-THE-FUEL-CURVE