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Is MTBT always the same regardless of AFR? Example, can you set timing and say change out an intake and listen for knock but not redo timing on a dyno? Just adjust the AFR?
In short, no. The MTBT depends on the engines design and VE plays a big part of this, if you change an intake you're changing the VE of the engine and therefore the MTBT point. If your engine isn't knock limited you could end up over/undershooting your MTBT point and sacrificing power so your adjustments should really be done on a load bearing dyno to find your MTBT again. You also won't be able to hear knock if you're not knock limited since you are able to reach MTBT.
I agree with Chris - Any time your changing engine components that affect the engine's VE, the optimal timing can also be affected. If the part your changing has a minimal effect on VE then it's quite likely that the timing won't need to be changed as there is a plateau around MBT where you don't really see much change in torque as you vary the timing. If you're seeing a significant change in VE however, you may need to spend some more time on the ignition table.