Help: I need a Spark

[Jagdwuf]

I have built a combustion cannon and for safty reasons I want to run a long electrical wire from it to a firing box. I need someway to get enough voltage that I can have a spark jump from one bolt to another inside the chamber. I think I can do it with two car batteries and a motorcycle coil but Im not sure how.

Im smart in many ways but not when it comes to electricity.

 

[[f]]

I would just use a potato and stick some big peices of copper into it when u needed some juice.