They are the same, but the water neck out is angled a lil different.

I have a NNBS water pump on mine.

 

That is a good idea as theoretically different diameter crank balancers and idelers along with different idler placement will change the positioning of the 'slack point' along the travel arc of the tensioner.


I was doing a little thinking about it last night and drew up a quick acad sketch this morning to make it a little easier to see and explain. In order for the tensioner to be most effective with the proper length belt, the full tension stop of the tensioner (referred to as 'slack point' above) should be perpendicular to the belt force line from the crank to the idler. Otherwise as the travel goes beyond this point in the opposite direction, it adversely starts applying tension to the belt therefore reducing the amount of tension travel in the preferred direction.

 

Any new news on this? How is it working out?

 

Care to explain why 90* is preferred vs parallel? And what bearing does the imaginary line have to do with anything?

 

The imaginary line has everything to do with it. Visualize grabbing the belt on the other side of both the crank and the idler and applying force in each direction. If the tensioner were not there what path would the belt take? The imaginary line. Now add the add the tensioner back in but allow it to free spin at the pivot point and apply the same forces on the belt. Where is the tensioner arm going to stop? On the perpendicular line as it is the shortest point from the belt force path (imaginary line) along the tensioner's travel arc. Therefore applying force with the tensioner to the proper length belt, at this perpendicular position the tensioner would be applying the least amount of tension on the belt along it's travel arc. For this instance of the tensioner spring applying force in a ccw direction, anything from this point 180* ccw would apply tension on the belt but would require a longer belt the farther ccw the arm travels. However, anything beyond ~90* ccw, the belt would likely make contact with tensioner spring casing.

 

schino, check your PM

 

I disagree

The imaginary line would stay the same regardless of tensioner location, so moving it would yield less than satisfactory performance. A more general method is to imagine the tensioner pulley floating free in space. If you moved it along the belt path since the belts length is fixed, it will travel in an eliptical arc. Setting tensioner arc perpendicular (to the tangents) to this path keeps the tensioner spring focused solely on the belt and not excess travel. Think about it, whats the best way to pull something? Straight on or off to an angle

Ive built several custom SC setups and this method seems to work the best. It also explains alot of the common problems truck guys have with their kits. If the tensioner goes to the minimum it cant put adequate tension on the belt so slack is introduced then the belt flies off. When the tensioner maxes out on the mechanical stop, the belt will continue to pull, so the tensioner fractures. The HD kits dont seem to do much more than bandaid the issues. Most people buy them for the stringer spring when the real reason they work better is the increased travel. Rethinking the issues and tweaking a few things makes the current parts (which are fine) work better with the given system

Now, think about why increasing the travel on a design like you posted helps. Heres a trace of the simple diagram you posted, granted nothing is to scale but you can see the general idea. Now Simulate 1" of belt stretch. Look how much extra travel is present using the imaginary line method

How does this pertain to the OP and his custom bracket? Change the design to rotate the swing up using a longer belt. His WP neck may get in the way, so redesign the bracket to have a mount lower to the water neck

 

I agree with the force representation in your illustrations, however, it relies on being able to move the mounting point of the tensioner, which we are not able to do in this particular application. I think both of our methods of thought would prove that with the tensioner mounted above the mid point of the imaginary belt force line, tensioner travel below the perpendicular line would be wasteful (which was the original point I was trying to make).