[custom funvehicle] Need idea\'s

[w00p]

and, you, of all things, didn\'t mention the custom watercooling plans???

Anyway, these days I\'ve been doubting, and, if you ask me, it\'ll be easier to make a little chopper or something like it frame-wise after all.
The only problem I then have is finding info about the centre of mass of the engine and all other parts. I\'ve learnt about centre off mass in school of an object made out of one material, but could someone tip me in on one to calculate a centre of mass of an object consisting of different materials?
And possibly a small online index of the (forgot the term, the unit is in Kg/M?) of some materials that would be of common use.

Oh, and, izzy, is it possible to stick-weld aluminium?
How much amperes should your welder be able to pump out?

Also, does anybody know where I can find a general tachometer to measure the engines rpm\'s?