This is not anouther arguement for which is better... But it is a question about if there is a way to tell the difference between an S4 NA and an S5 NA if it has been removed from a car and is just sitting in the floor?

 

If they are complete, the S4 has a mechanical oil metering pump, while the S5 is electric. The TPS on a S4 is single, while the S5 is a 2 plunger unit.
It's a start!

 

IIRC s5's don't have the EGR thingy on top of the engine.

 

s5 knock sensor is on the front s4 is on the side IIRC.

 

also the S5 has the VDI manifold

 

Intake manifolds will do it. It's the most obvious difference.

 

No knock sensors on non turbo FC engines