Heard the engine heats up the pvc and it releases toxic gasses into the motor. Not sure how toxic or how much but I would steer away from it.
ABS is the only way if building your own.
Unless you go with an aluminum tube.
No doubt PVC off-gasses when heated. But, does this really affect the motor? The motor is already pumping much stronger gasses and chemicals just with the gasoline and whatever additives it contains, including upwards of 85% Ethanol (which is an alcohol and is corrosive to aluminum). Sure,
humans should avoid breathing in the PVC vapors, but just as much as they should avoid breathing in gasoline vapors, too.
I agree with using ABS. I find that it's easier than PVC to work with when softening it with heat to reshape it. Plus, ABS pipe and cement is just as available as PVC stuff in the plumbing sections and it's already black like the mass-produced ABS intake tubes.
The only real hurdle is adapting the standard pipe sizes to the MAF and TB inlet diameters.