Depends on the mods, mods and boost alone can greatly affect AFR. Along with fuel octane. 91 and 100 burn differently. This is why we perform tuning for different boost levels and fuels. You can have two cars with exact mods and have a totally different tune. We try to get as close as possible to one's mods and fueling. So many variables even like one's fuel pressure regulator, fuel pump can throw things off.