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

[justbob]

The first thing I’d do is replace the OEM tensioner with one more subtitle for boost like a Thump or a Roush.

I’m not familiar with this set up but is there anywhere you can add an additional pulley on the left side timing cover stand off? I had one on mine that I bought off Jerry even though I didn’t really need it as my supercharger was driven by its own belt and both belts were set up with manual tensioners.

8 rib swap?

Other than that a Gates Fleetrunner (green) belt is the best I’ve ever heard of or used. I was able to achieve 20.5 #s on the old Trilogy set up I had prior to the Centri. Of course that was coupled with the smallest pulley up top and the largest pulley available on the crank and a Thump RRR Racing tensioner to keep everything in check. Also keep in mind a Trilogy is also separately driven and it’s 8 rib, not 6. Never once slippage, just completely unusable boost as I was really only making heat at that point..


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[azgolfrat]

It looks like there is a spot on the drivers side timing cover. A pulley would fit there...close to coolant line, but I think it would fit...
Do you know the recommended diameter of the pulley to be added? I've tried to upload a photo of the location...but the site says I am over my quota?

[justbob]

PM Jerry, lij372


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[blazen71]

I don't think the pulley will work. A pulley will physically fit with Gerry's spacer, but the belt will end up hitting the Vortec Idler pulley bracket that's below the Alt.