Hi,
I use a 24awg 450turn trifilair, with 2n3055 transistor. Works good. The coil was made from an old waterpump-motor from a washing-machine. The core consists of stacked strips (which was a long job to remove without damaging). I just start to charge battery (4Ah,12V). I dump around 100-120V in there (4.7 microfarad/250V cap).
Timing of 555 gives strange effect on oscilloscope. with slowing down the timing of the 555, the voltage over the cap increases, but it stalls at 120V. Dunno why it stops there.