For many years engine builders and tuners
relied on reading spark plugs to determine proper jetting. Then along came
data acquisition and they started using EGTs (Exhaust Gas Temperature) for
additional information on how the engine was running. Many still rely on
EGT.
In the mid to late 90’s the price of
equipment to measure actual Air/Fuel ratio has
come down to the point of affordability for builders and tuners. The best
arguments for measuring Air/Fuel ratio rather than EGT are:
- The amount of Air and the amount of Fuel
being put into the engine is something you have control of generally.
Hence, the Air/Fuel ratio is a direct measurement of how the engine
responds to the changes you make.
- The EGT is simply a by-product of what
is going on in an engine. It is an indication of how the engine responds
to changes rather than a direct measurement.
- The simplest example of how EGT can
deceive you is when you are running so rich that you are burning fuel in
the exhaust pipe, causing very high EGT. Normally a high EGT reading is
thought to indicate a lean condition, but in this example the engine
would be very rich.
- Measuring actual Air/Fuel ratio on the
dyno enables you to know at which Air/Fuel ratio your engine makes
maximum power. You can then duplicate this ratio at the track.
