Tighten Your Belt
Maintain big boost without belt slip thanks to VMP’s billet GT500 tensioner
By Steve Turner
Owners of 2007-2014 Shelby GT500s know how easy it is to build power with these cars. Just add a smaller blower pulley, open up the inlet, add a custom calibration and the gains are huge. As you start to push harder with smaller pulleys, more rpm, and such the factory belt tensioner is put in a bad spot.
When you bang through the gears, the on-and-off load puts a lot of strain on the factory’s cast, spring-loaded unit. Over time the stock unit can weaken and in some cases it can even fail. Such failure can wreak havoc in your engine compartment. Even if the tensioner doesn’t give out, the excess movement allowed by a worn or overwhelmed stock unit can lead to belt failure.
“We developed this tensioner to help out the guys that are running a lot of boost and bigger superchargers,” Justin Starkey of VMP Performance explained. “The problem is the factory tensioner is heavy and weak.”
Unlike the stock cast unit, the VMP Heavy Duty Tensioner for 2007-2014 Shelby 5.4-/5.8-liter (PN VMPGT500HDT; $399.99) is machined from billet aluminum, so it won’t crack. Moreover its spring delivers 20 percent more tension than the factory tensioner, which will allow for more consistent, slip-free boost.
“The improvements that our VMP tensioner brings is a much stiffer internal spring that helps control the belt better and provide more tension and thus prevent belt slip,” he said. “One of the other ways that it is better is that it uses a much lighter, billet aluminum pulley and it is much lighter overall. That reduced sprung mass allows it to react faster when you are racing and shifting hard and basically take better care of your belt all around, which is incredibly critical on a supercharged application.”
For a bit more on the tensioner you can watch Justin give an overview and install it here…
[video=youtube;G7Wea6ee2zA]https://www.youtube.com/watch?v=G7Wea6ee2zA[/video]
The best part about the VMP unit is that it’s easy to swap out your stock unit and bolt the VMP billet tensioner in its place. To see just how easy, we hopped in our own Project Vapor Trail and headed to VMP Performance to document its installation on our 2008 Shelby GT500.
Here’s a look at the factory supercharger belt tensioner. This cast, spring-loaded unit is designed to keep tension on the blower belt at stock performance levels and rpm ranges. Once you start pushing more boost and rpm, the factory unit can become a liability.
It’s a shame that VMP’s billet beauty (PN VMPGT500HDT; $399.99) disappears down into the FEAD where it isn’t too visible. However, with a more rugged construction and a 20-percent stiffer spring, it will reduce belt slip and eliminate potential failure. It is available with either a 75mm or 90mm idler pulley to accommodate your belt length.
PVT rocks The Tank from M-H Racing. This fetching unit aesthetically joins the engine coolant and intercooler reservoirs for a clean look. Because they are joined, VMP’s Justin Starkey disconnects the intercooler hose and swings the tank out of the way.
Use a long-handled ratchet to loosen the factory tensioner so you can remove the belt from the blower pulley. Don’t remove the whole belt. Simply remove it from the upper pulley and leave it be. Leaving it routed will make it easier to put reassemble the FEAD. Then you can loosen the factory tensioner bolt and pull out the stocker.
The only part you need to swap over to the VMP tensioner is the bolt that retains the idler pulley.
Use the stock bolt to install the VMP pulley. Even this pulley is a major upgrade as it features a heavy-duty bearing and weighs half as much as the stock idler pulley.
Once you line up the two dowels that lock it into place, you can bolt it on using the supplied fasteners.
After bolting up the VMP tensioner, you can use that long ratchet to loosen its tension—it will take more grunt than the stocker did—and reinstall the blower belt. Have some one watch the belt as you crank the car with you foot to the floor so it won’t start. If the belt alignment looks good, you can reinstall the coolant tank.
After reinstalling our M-H Racing tank and putting the rest of PVT back together, Justin pressurized the tank with compressed air and bleeds the air out of the system. You can do this with a small plunger if need be, but you don’t want air bubbles in the hoses as that will keep the coolant from flowing through the intercooler system.
