Better (best?) belt for the V7 JT ADTR config

[azgolfrat]

Hey Guys,
I've had ongoing belt slip at the SC pulley since startup about 11 months ago. I've been shrinking the belt size incrementally and I think I found the correct length.
The belt that seems to reduce slip significantly is the gates K061099. It's 110.5 inches on the outside circumference. Because I saw a good deal on a K061098 (about 1 inch smaller OC) I bought it and tried to put it on; too small.

1) Best evidence of prior slip was black dust pile up, right behind the SC pulley, which unfortunately isn't visible unless the SC is taken off the engine
2) Max boost achieved prior to the 1099 belt was ~ 6.6 lbs, while just after putting the 1099 on, I was able to get 10+, and there was more to go...I ran out of road :-)
3) Using a torque wrench I discovered that the torque required to move the OEM tensioner (Motorcraft BT-68) increases as the tensioner is rotated further and further to its movement limit. I think this is important as it means that a smaller belt will be held in place with more torque than a looser belt. Unfortunately, it also means that as a belt stretches it will be held in place with less and less torque.

I did notice that at around 10lbs, 6500 rpm or so, the engine stumbled a bit...I thought I read somewhere the ECM does this for some reason? (I did have the traction off and the overdrive off).

As always, thanks for the help guys.
-KK