Hi,

Its a little more complicated than that..
The valves are in an engine among the most technical parts created(you could write an entire book just about them!).
It has to be/have:
1/ high thermical resistance(in NORMAL run condition an exhaust valve has a dark red colour...)
2/ high mechanical resistance(open/close +100 times a second!)
3/ lightest possible, to reduce weight forces, when it changes direction from up/down, GGeeee!!
4/etc etc..

We all know the valves change size when warm; they becomes longer, thats why you need a clearance to be sure they won't stay open...and COOL DOWN when closing correctly.

The exhaust gaz flow has the same temperature or less than the highest one inside the cylinder..(when you use bike as build by yamaha)

The OEM pipe is not empty and creates compression inside the exhaust as the gaz flows out the cylinder; let's say the exhaust is filled with burned gaz...

What happends when you put oxygen to a fire?
The valve "tail" will be affected!!

Valves have a maximum of thermical tolerance depending on the material they're made of..
above they'll burn(exhaust valves especially), above the "calories/heat" won't be evacuated properly but transmitted to pieces in contact with the valves..
Airplanes have valves filled with liquid sodium, to fly up there...
Ténéré's have valves made of a steel mixture.
Newer bikes have titanium valves; lighter; more rpm.

I won't say the lazer pipes etc are crap; they are performance products made for racing.
But they are not engine life products.
I think one wouldn't buy an exhaust if he wouldn't feel an improvement to the engine performance..


Gosh, that was hard in english!
I hope I explained "clearly" though.

Cheers,

Matt