Maybe 1/16 of an inch or a touch more, I do have some heat repelling material sewn onto the outside of a different engines diaper but also being so close makes it kinda a pain to get the diaper pulled up around that tube. I had to do the same thing to the other set too so not a huge deal it's just something I wish I didn't have to mess with but it's my fault as I insisted, lol, basically that he built these for me off of Chris's car and there are some differences between the two setups that does effect things.