Is AFR recommended for cars and bikes different?

Hi guys! Am I understand right that for cruising AFR should be about 14.7? If yes,don't you know why it's considered lean among bike tuners (for cruise also)?

For light running, like when cruising under light load, normal practice is to run leaner than stoich'.

The reason is when cruising one is not interested in maximising power, or torque, but in getting as much useful energy out of a specific amount of fuel - best fuel consumption, in other words.

For gasoline you're probably going to be looking around 16:1, or around lambda 1.1, but it may vary a little either way, depending on the fuel chemistry and engine characteristics.

Don't forget the ignition timing, too - that can make a BIG different (up to 30%, or even more in some instances) on light and part throttle economy and response when properly advanced.

Good question that I share as well. I have also been seeking specific information on tuning bikes too. With very small displacement compared to car engine (i.e. 600cc trackbike), what the differences are, if any, when tuning such small displacement and high rpm (my R6 revs to 16,000prm).

My thoughts, bearing in mind I'm not really into bikes, is a smaller displacement engine, because of the square-cube relationship between capacity and surface area of the chanber, will lose more energy to the engine, and so should be able to use a higher compression ratio for the same fuel octane - more compression heat being lost to the chamber surfaces proportionally, and this seems to be born out in practice.

Other than that, the basics of fuelling and timing for best torque through the rpm range for that engine should apply.