range - belt tensioner - fox mustangIf you have underdrive pulleys, in most cases, you can use the stock belt size and the tensioner has enough “wiggle room” to accept the new setup. Typically you want the belt tensioner to be around the middle of the “range”, this will allow it to provide the proper tension. You should note that the pulley on the tensioner is held on with a reverse-thread bolt. That means you have to “tighten it” to remove it. This is also a good opportunity to replace the tensioner if it’s worn out.


Serpentine Belt for 5.0L HO

  • For AC equipped: DAYCO 5060905
  • No AC: DAYCO 5060845

belt routing factory fox mustang 5.0L HO

I honestly don’t think it would make a difference in bypassing the air pump, since it’s not really “in use” during WOT (learn more about smog stuff here), but if you have AC, you could bypass the power steering and air pumps. The AC is basically just an idler pulley when not in use. The “73 inch belt” routing in the middle may cause you problems due to the tight fitting between the two belt passes between the tensionner and the water pump pulley. Another option “V2.0”, if you have the room, will fix that issue. You will have to watch out for the direction the water pump pulley is turning to ensure you don’t cause an overheating issue.

bypass smog - belt routingMay Need to Test for Under Drives

My 5.0 with no AC and SVE underdrive pulleys needed an 83.7″ belt – the 84.5″ belt I had obviously didn’t fit. You can use the old “string trick”, find a string that’s at least 100 inches long and wrap it around the accessory drive, mark where it completely wraps around. Measure the string and start with a belt that’s a 1/2″ shorter than your measurement. Honestly, to make life easier… buy a few sizes down and up from your measurement and return what you don’t use (just don’t start the engine or do anything to scratch or ruin the belt or you risk having to keep it!).

Under drive pulleys