Some drives burn "hotter" than others?

[katzdvd]

I burn 4 discs at once (in succession) with IMGBurn Queue; I have Benq (2) 1655's & (2) 1640's. I have noticed that the discs are quite warmer to the touch when finished burning on the 1640 drives, than they are with the 1650's.

Any thoughts on this?