PVC is not meant for high temperatures.
Everytime you drive, a small amount of gas is given off by the PVC, and you are more than likely inhaling some of it.
Even these small amounts, overtime, will make you sick.
I am using some PVC for my intake as well, but only in the wheel well were it doesn't get very hot.
The PVC is not MELTING, it is burning off.
I would also not recomend ABS plastic either.
Most plastic used in engine bays is PC-ABS (a high temp non-toxic poly carbonate plastic).
