We've featured the V8 engine paper model at Yee's Job before, but they've just released a new (working) paper model of a V12 four stroke engine:
It took approximately two years to design this spectacular magical art for you to put together. This “V12 four-stroke Engine” has semi-realistic exterior and interior detail. Each of 12 spark plugs (LEDs) is ignited accordingly to the moving cycle. Many moveable parts include a compound crankshaft, a rapid cooling fan, 12 rods and 12 pistons etc. It is made with paper entirely (except some little wood sticks, some tapes, some LEDs, some electrical wires, some switches, a motor and a battery holder).
There's even a DIY Kit for sale (595 pages of instruction with over 1,000 illustrations!): Link - Thanks German!
Why not make a car entirely out of paper, except for the engine, the wheels, etc...