OK I'll start from the beging.
Bought an 04 G35 sedan two weeks ago. Today I installed a KN filter and removed my intake resonator. Had nkind of a funny smell first few minutes. I took the car for a drive, and after a little bit of hard driving (5500 RPM Shifts 6MT) returned home. Still had a little smell. So go out with some friends to eat. On the way home to have some drinks after dinner, my friend and I decied to have some fun. He drives an 03 350. We line the cars up on a back road by my house. We racde for about 1/8 mile. As I turn around to go to the house, after the race I noticed the clutch became soft and stuck half way to the floor. I know the KN filter and the clutch have nothing in common. But one: whats that smell after the KN install and Two: Whats up with my clutch? By the way ran good with a stock G Sedan 6MT aginst a stock 350 6MT. Sorry so long winded just wondering.

 

The funny smell after racing would be your clutch. Same goes for the pedal getting spongy and stuck to the floor. Either you slipped it too much or it simply can't handle WOT blasts. It basically means you overheated your clutch, pressure plate, and scoured the flywheel.