I have a Kyosho 2.0 starter box and want to get a higher amp lipo battery.

I understand the C rating is how much discharge current it can handle. Im not sure how much current the starter box motors need 2 x 550 motors) but, for e.g. if a 20C battery is enough for the motors, will a 40C make the motors turn faster?

Will a higher C ruin the motors if they can take in more current or will the motors spin/use only what its max current it so higher C will not make a difference.

May need to change the current deans plug to a bullet. Is there a difference in the thickness of the wire? Will a 10awg wire be better than 12awg for a higher mAh and C rated lipo?

The 2x550 motors in the starter box will only pull as much current as the need subject to the packs ability to provide it. No matter how much current the battery is able to provide it's the motors that pull the current, it isn't 'pushed' by the battery. So a higher C rating lipo wouldn't damage the motors.

The 550's that we use in our starter boxes are high wind motors for torque and don't really pull serious current. I use 5000 25C packs in my box and can easily start tight .21 novarossi engines (preheated of course!) without any issue.

The way the C rating works is you take the capacity and multiply by the C rating. So a 5000 lipo with a 25C rating would be able to provide 125A discharge which would be plenty to power 2x550 motors used in a starter box.

In summary, only higher VOLTAGE will make the motors spin faster. The current drawn is dictated by the motors. A 5000mAh 25C lipo is more that enough and I would have thought your running 4s (14.8v).

The difference between 10 and 12awg wire is negligible. 10awg will be able to take more current that 12awg but is more bulky and more difficult to solder well as you'd need at least an 80watt iron. Just use 12awg, 14awg is more than enough actually.

Hope the above helps!

FWIW I have the same box. I think it came with Tamiya style plugs for the batteries. I cut those off and soldered Deans plugs on as those match my 4s lipos... 65c. No issues.