Your racing engine blew up. Now what do you do?

After that, you repair all the mechanicals that are broken. You review what went wrong. You revise your tune-up to try to avoid it again. For fuel system adjustments, try precise numerical control over tuning using air/fuel ratio!

Without knowing it, this is something you already do:

  • When you adjust fuel injection jetting from plug readings, you are changing air/fuel ratio.
  • When you adjust fuel injection jetting from exhaust temp, you are changing air/fuel ratio in each cylinder.
  • When you adjust the blower overdrive in blown engines from spark plug reading or exhaust temp., that is air/fuel ratio tuning.
  • When you adjust the boost in Turbo cars from spark plug reading or exhaust temp., that is air/fuel ratio tuning.

You can control these situations with precise air/fuel ratio numerical control. For a more finely tuned setup, you can find out what your ideal air/fuel ratio is and adjust your setup to maintain that ratio.  When you don’t know the ideal air/fuel ratio for your engine setup or what it is after you make a tuning change, tuning is going from one result to a new one without being fully in control of the outcome.

Some setups are overly rich or overly lean. Spark plug readings and exhaust temperatures are misleading. Some setups have momentary overly rich or overly lean stages in an otherwise good setup. Here are a few scenarios that may occur:

  • forward facing scoop increases air into an engine with speed (leaning out the air/fuel ratio without suitable enrichment)
  • air density changes
  • temperature changes
  • barometer changes
  • humidity changes.

Air/fuel ratio can be measured with an O2 sensor, however, readings are probably only accurate for fuel mixtures near the stoichiometric AFR ratio. In high output racing engines that are run rich:

  • excess fuel enrichment to retard detonation can cause O2 sensor error
  • after burning in the exhaust can cause O2 sensor error
  • excessive camshaft overlap causing intake dilution into the exhaust can cause O2
    sensor error.

The best way to determine AFR is to calculate the ratio of the weight of fuel to the weight of air.  That can be determined from the weight of air going through the intake system and the weight of fuel going into the engine. A good air/fuel ratio has good performance and good spark plug color. Adding air/fuel ratio numbers to your racing records is a key to long-term success.

Learn more about this and other factors that make a winning engine combination in our online book store.