Tuning richer than 0.90 Lambda

I just finished the lesson on choosing the correct AFR and it was mentioned to avoid fouled spark plugs, lubrication washed off the bore walls and sump oil being diluted with fuel its best not to tune richer than 0.90 Lambda. However it was also mentioned that maximum power for a naturally aspirated engine is typically achieved between 0.85 - 0.92 Lambda and for forced induction engines its between 0.82 - 0.85 Lambda. My question is even though a forced induction engine produces its best power between 0.82 - 0.85 Lambda should I still avoid tuning richer than 0.90 Lambda? (Apologies if this has been asked before)

There are two things to consider - peak torque/power when running excessively rich may give more with the correct tuning, and when one is not leaning on the engine and one can run around lambda 1.0, or even leaner, to avoid the issues you mentioned.

Different engines will respond differently, and while I might look at around 1.0 at idle, dropping to around 1.1 under light throttle and load, richening up to around 0.9-1.0 around the transition from vacuum to pressure in the manifold and going to the 0.85-0.9, or what works best, as peak cylinder presures/load is approached, that may not be the optimum for you. There is a thing called "lean best torque", or "lean best power", where the engine is run where the best output, per unit of fuel, is obtained, rather than just raw 'power'. If it's a daily driver, this can save 10-20% on fuel use, which is nothing to sneer at with current prices.

A complication is that some emissions vehicles are made to run at stoich' for best combustion and minimal pollution, and some countries/states have exhaust "sniffer" tests.

Trent,

I love that you're bringing the various bits of info together and trying to make a plan.

Generally you want to avoid enrichment during idle and cruise, and only enrich the engine as needed to meet your needs for performance and component protection during aggressive driving. If this is for street use in an emissions controlled environment the story gets a lot longer, but for now I'm writing this as if this is for a racing scenario.

As throttle and load increase, you may need to increase enrichment, but you don't need max enrichment as soon as you touch the throttle.

By avoiding enrichment from lambda 1.0 until it's required, and only enriching as much as needed, even on a forced induction application you only end up rich of 0.9 lambda for a small portion of engine operation.

Restricting when the enrichment occurs dramatically reduces bore wash and oil dilution. So it's not just the richest lambda value used, it's the time spent in that condition as well. For example a forced induction application may idle/cruise at 1.0, run 0.9 at a few psi boost, then ramp down to 0.78 lambda at high RPM and full boost, but it isn't going to operate at 0.78 for more than a few seconds at a time. In that scenario that enrichment may be what's avoiding the pistons melting, so it's an immediate need that overrides potential concern for a little fuel getting in the oil.

Please let us know if that answers your question.

Thank you for the highly detailed answers from the both of you that clears up the questions I have on the topic and hopefully helps anyone else with the same questions

Awesome, glad to hear it.