Wrenchin’ Tip – Fuel Delivery

Here the first Wrenchin’ Tip for 2011.

When installing a new engine or even modifying your present power plant fuel and intake system you have a few things to consider.

Of course the size of your fuel pump, where it and the fuel filter is located, size of the filter, size of your fuel line, fuel pressure.  Along with that jet size or injector size and baffling in your fuel tank.  All of this is important to ensure your fuel delivery system can maintain full pressure at peak engine horsepower in high gear.

All of these need to be adjusted or “sized” to accommodate less controllable factors such as Altitude, air temperature and idiosyncracies of your fuel, like quality and octane rating.  Yes even specific gravity of your gas can effect the jetting.

Here are some jetting requirement of a 750 CFM 4 barrel Holley for specific fuel, temps and altitude options:

Octane                 Temp.            Altitude      Front Jetting      Rear Jetting

  94                        80F                 0 ft                   81                       86

110 Race              80F                  0 ft                 81                       83

94                          80F                3000 ft           76                      81

94                          80F                6000 ft           73                      77

94                          40F                0 ft                 84                      89

94                         120F               0 ft                 78                      83

Oxgenated fuels toss another factor in to be considered when determining your jetting requirements.

Studies of shown that every 1 point richer in air/fuel ratio equals only a few percent less power.  Running the engine as lean as possible will increase your power but also increased combustion chamber temp, which can damage your engine.

Thanks for reading