wire a spark plug to a switch then drill a hole near the tip and wire plug to power source also (duh) and push switch and it will light unburned gas on fire make sure u dont turn ur car off with the switch on because flames will shoot back up ur exahust and into ur engine folowing the gas and then BOOOOOM.....

edit:
or u could have one of those small propane tanks...one of those portable grill ones...have a tube and ligth thingy to a hole u put in ur exhaust and then turn knob to propane and switch to light it.....that would also work (saw that on monster garage hehe)