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AFR and combustion chamber

EFI Tuning Fundamentals

Discussion and questions related to the course EFI Tuning Fundamentals


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How do you know how hot the combustion chamber is so you can use the AFR to manage it? Do you listen for knock and then make it richer?

i may be missing the point of your question, but what application are you thinking of?

I stand to be corrected, but I would prioritise timing and then work that with the mixture to get best torque while, if turbo'd, keeping it below the manufacturers maximum recommended exhaust temperature.

Temperatures are normally a concern with turbo-charging as the turbine in the hot side is usually temperature limited by the material(s) used in their manufacture, so a thermo-couple is fitted in, or close to, the turbo' housing exhaust entry and used with suitable guage(s) and/or directly monitored by the ECU.

With NA engines it can be monitored with thermocouples in the exhaust manifold(s) as close as practical to the exhaust port and is more of a tool for tuning V8s which use plenums as they usually have fuel distribution issues and as a result different exhaust temp's - lambdas (oxygen sensers) do the same thing but are more expensive.

It's not the combustion chamber temperature most look at, it's EGT (Exhaust gas temperature)

For that you need a k-type Thermo-couple mounted in each header (Or at the very least each bank)

Richer mixtures are a help, but they're not perfect.

Most of your temperature will be determined by things like compression ratio, fuel type, IAT, ignition timing, EGR percentage and how much power your making.

Thanks for the replies! I understand now!