Battery & Ignition timing

Replacing into new 75D23L car battery for SXE10 TOYOTA Altezza brought tremendous improvement in the performance of YAMAHA 3SGE motor. Combustion state became so smooth as to make me feel comfortable and accelerating pedal reaction changed into more vigorous not roughly but gently with good fidelity. The fact was proved by three experiments that the motor performance would be far improved if the lead car battery was replaced into new one, XH200 OPEL B-Vectra, NVCP10 TOYOA Vitz and SXE10 TOYOTA Altezza.

As an experimental trial, two ignition timing was tested on VW 1302 Super Beetle today, following instruction manual 7,5 degree BTDC and 10 degree BTDC that is recommended by the most of the pioneers in this field.
As a conclusion I choose 10 degree BTDC with no hesitation, because the response of VW AD motor is far smooth and acceptable for me, but remember the another one must be suitable for emission exhaust checking in Legal Inspection, I feel like that by my experience?
The difference of 2,5 degree in ignition timing affects on Ride that is beyond the expected impact.