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Understanding AFR: Medium Boost/High Boost

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Medium Boost/High Boost


00:00 If we are dealing with an engine running forced induction, applying full throttle will have the engine move into positive boost.
00:06 The amount of boost pressure the engine runs will be a function of the turbo or supercharger installation, and its important to understand how this can impact your target AFR.
00:18 As we increase the boost pressure, the amount of load on the engine increases.
00:23 We have more air and fuel moving through the engine and hence the combustion pressure and temperature rises.
00:31 This means as boost increases we need to adapt our target AFR to move richer also.
00:38 I have taken two arbitrary points in this map to illustrate how the AFR changes with boost, however the actual boost levels you choose to run may vary.
00:49 At a boost level of around 1 bar or 14.5 psi, I will start with a target AFR of 0.80-0.82.
00:59 As we move higher in the boost, the AFR moves richer and at 2 bar boost I would start by targeting 0.78-0.80.
01:08 I have proven these targets to be a safe place to start tuning, and they will result in good power while controlling combustion temperature.
01:17 There are some instances where we may want to modify these starting AFR targets and we will look at these a little later in this section of the course.

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