• • It is made up of two stock tensioners, custom spacers, “stop” modifications and fasteners.
  • By using two tensioners you are guaranteed of never bending it. It’s incredibly stiff.
  • Running double the spring pressure puts the belt tension exactly where Dayco/Gates recommends that their belts be run for maximum load (20in.lb/rib cold). We picked up a belt tension gauge to be sure. It does not over-tighten the belt.
  • And one of the most important ingredients in it working so well is that the stops are modified so the tensioner has more travel. This prevents the tensioner from hitting its stop(s) during gear changes, banging the rev limiter and spin/hooking the tires. Which bends tensioners, throws belts and beats up crankshafts and breaks oil pumps.
  • This is the only tensioner available that will never bottom on the stops.
  • This is the only tensioner available that has this much spring pressure.
  • This is the only tensioner available with as much travel.
  • This is the only tensioner available that comes with the correct spring preload information so you can be sure that your tensioner is working at peak performance.
    • Best functioning tensioner kit available for the 2005-2010 Mustang… period
    • Will never bottom out and shock the crank snout/oil pump gears
    • More spring tension and therefore less belt slip than any other tensioner available
    • More travel for slip free and bottoming free operation
    • Inexpensive
    • Impossible to break or bend

    We designed the FT back in 2006 when we couldn’t keep belts on our Kenne Bell 2.6L. At the time we figured we would use it for a short period and come up with something else for the long run. But it worked so well an no one (including us) has come up with something better, so we stuck with this design. Since then the Frankentensioner has ended up on a minimum of 500 cars, and has worked flawlessly. It’s not going to win any art shows but it works fantastic.

    Features/Specs:

  Kit Contents

  • Tensioner body spacers x3
  • Tensioner arm spacer
  • Fasteners
  • One tensioner to go with the existing one that is already on your car

Some assembly/modification required. Click here for instructions.

Belt Tensioner Tech

Belt tensioners are very misunderstood or maybe a better word, if it’s a word is under-understood. A belt tensioner has a lot of jobs. And when you add a supercharger to the mix more yet.

Let’s start off by making it clear that the stock/OEM serpentine belt system was not designed to run a supercharger in any way shape or form. So right from the start we have that going against us. Don’t lose sight of the fact that the supercharger is not supposed to be there. If you look at most OEM supercharged cars they have a separate belt to run the supercharger with a wider belt and a beefy tensioner.

The Tensioners Job

The belt tensioner has a lot of jobs. The main and simplest one is to provide enough pressure to keep the belt tight so it doesn’t slip. It is also responsible for taking up the slack in the belt as it stretches under load. Lastly the tensioner is supposed to not allow the belt to go “solid” or tight (more on this below). That is a lot of jobs for something that is so simple, and it gets a whole lot more complicated when a supercharger is added to the mix.

Spring pressure

The tensioner has a spring in it, that is what provides the tension/pressure on the belt. The spring is a “progressive” rate spring. I could spend pages outlining the difference between progressive and liner rate springs, but I won’t. If you want to understand the difference in detail a quick search will get you all sorts of information. The short version is that with a progressive rate spring the further the spring is compressed the more the rate (stiffness) goes up. For a tensioner this is good, for something like a valve spring, not good. The OEM tensioner was designed to cope with the stock accessories, not a supercharger and the stock accessories. In simple terms think of the accessories and supercharger as “weight”. The more “weight” you have the stiffer the spring needs to be. Clearly when adding a supercharger you need a stiffer spring. But why?

There are two reasons why you need more spring pressure. The first one is simple. Because you are adding a supercharger, which “weighs” a lot more than the accessories the belt needs more traction/pressure or it will slip on the supercharger pulley. The second reason is more complex.

When the motor and supercharger change speeds dramatically in relation to each other, like during a gear change, hitting the rev limiter or spin/hooking the tires the belt wants to go “tight”. The rotors in the supercharger represent quite a bit of weight (much more than the spinning parts in the accessories) and a lot of kinetic energy. When you make let’s say a gear change from 2nd to 3rd at redline the engine drops about 2,000rpm. The motor is directly hooked to the transmission, rear end and ultimately tires which means that the RPM’s drop instantly. The tires contact with the road works like a brake for the motor. The supercharger on the other hand is spinning at 13,100-18,000 rpm and is being slowed down to 8,700-13,600rpm during that gear change. The “problem” is that the only thing slowing the blower down is the motor, which it is connected to it by the belt. Well, that belt isn’t terribly happy about slowing the blower down and what happens is that the belt goes tight, real tight, and tries to slam the tensioner off of its maximum travel stop. This is a problem, a couple of big problems.

The belt can/will slam the tensioner off of its maximum travel stop so hard that it will bend the tensioner arm. Take a look at your tensioner………how hard would you have to hit that arm with a hammer to bend it? Pretty hard huh? I have even seen tensioners ripped off the front engine cover! That’s hard! The first and most dramatic problem with the tensioner bending is that the pulley is now at an angle and the belt comes off. You can put it right back on. But it will come right back off again as soon as you start the car. You’re stranded. I’ve also heard of belts breaking but I have never seen it. Most people at this point put a tensioner with a stronger arm on, it doesn’t bend anymore and all is good, or is it? The answer is no, it is not “all good”, far from it. The only thing a stronger tensioner arm does is make it so you aren’t stranded on the side of the road from bending, which is a good start. But it doesn’t solve the problem. What is the problem?

The problem is that when you change over to a tensioner with a stronger arm and don’t increase the spring pressure or travel (more on this later) you have only put a band aid on things. You still have a big problem and that is the tensioner slamming into its maximum travel stop. All of the force that it took to bend that tensioner arm is still there, the arm is just strong enough not to bend. Now all of that force is transferred to the pulleys and crankshaft snout. Would you hit the end of your crankshaft with a hammer hard enough to bend a tensioner? Nope, that would be crazy. But that is exactly what happens when you bottom a tensioner. And it gets worse. The snout of the crank goes through the oil pump (it drives the oil pump). Whack the crankshaft hard enough and the oil pump gears shatter……and you just bought a motor. This is not uncommon, there are a lot of smoked motors out there because of shattered oil pump gears. So many that there are super high dollar aftermarket billet steel oil pump gears available.

No one knows for absolute 100% certainty what causes oil pump gears to shatter. Like most things mechanical there could be multiple causes. But, a large portion of motors with shattered oil pump gears have a supercharger and a tensioner that will bottom. We have never heard of shattered oil pump gears on a blown car running a tensioner that can’t bottom. It’s probably happened, but it’s rare.

So how is this solved? Partially it is solved with more spring pressure. A LOT more spring pressure. It took us getting a Gates belt tension gauge and doing a lot of checking before we got an idea how much spring pressure was really needed. When we built the first Frankentensioner we thought that we probably had too much spring pressure and would wear the pulley bearings out faster. But we didn’t care, worn out pulley bearings were much more preferable to bent tensioners and shattered oil pumps. Ends up that having double the spring tension (two tensioners) was just right according to the Gates and Dayco belt engineers. Yes, the tension is right at the top of the range, but just fine. We found every OEM and aftermarket tensioner that we tested (we did a lot of testing) didn’t have enough belt tension. About half of the aftermarket tensioners had more tension that stock, but still not nearly as much as you would want.

Tensioner travel

The most overlooked thing about belt tensioners is the travel. Travel is how far the tensioner arm will swing between zero tension (no belt on it) to bottomed out. The travel is critical to a correctly running belt system. The stock travel was never meant to cope with the much higher loads a supercharger puts on the belt.

Belts stretch a lot more than you would imagine. And the longer the belt, the more it will stretch. A 100” belt will stretch twice as much as a 50” belt. A stock belt is about 100” long. A supercharger belt is about 130” long. That’s 30% longer. Rough math says that right off the bat you need 30% more travel to deal with the extra belt stretch.

So how is travel connected to belt stretch?

Before you put a belt on your car the tensioner is sitting on its minimum travel stop (MTS). You put a pry bar/cheater bar on the tensioner, swing it down some and put your belt on. Note how the tensioner with the belt on is no longer on its MTS. It is somewhere in between the MTS and maximum travel stop. The reason you can’t have it on the MTS is twofold. Firstly because of the springs progressive nature there is very little pressure on the belt so it will slip. You need to have some preload (get into the spring more) for there to be enough pressure to keep the belt tight. The second reason is when the belt is loaded by the supercharger it stretches the belt and the belt gets loose. You need the tensioner to be far enough into its travel that when the belt stretches it doesn’t put the tensioner so close to the MTS that it loosens up and slips. Just set things up so the tensioner is further into the travel then, it will solve the problem. Right? Wrong. You also need to have enough travel in the other direction to deal with gear changes, etc that want to slam the tensioner off of its maximum travel stop. This is where travel becomes very important.

You need enough travel so that the belt won’t go loose under acceleration and enough travel where it won’t go tight (hit the maximum travel stop) during gear changes, banging the rev limiter and spin/hooking the tires. Tensioners with stock travel do not have enough to do both. You either get a tensioner that hits the maximum travel stop, loosens up under acceleration, or both. There is no way to cheat not having enough travel.

Conclusion

Just because you’re not chucking belts or bending tensioners doesn’t mean your tensioner is working correctly. You could still be slamming into the maximum travel stop (you probably are), experiencing a little belt slip during WOT/high RPM’s, or both.

We have never ever seen a tensioner that is strong enough, has enough spring pressure and enough travel aside from ours. Never.

Would we like to offer a big beefy awesome looking tensioner with enough spring pressure and travel? We sure would. Are we capable of designing and producing a tensioner like that? Absolutely. Is the market big enough for two super high dollar billet tensioners (there is already a high $$ billet tensioner out there)? Probably not. How many people can really afford to plop down $400 or so on a tensioner? Not as many as can’t. So, we offer a solution that solves all of the problems other tensioners don’t, and for very little money. Yeah. It’s not pretty. But at the end of the day what do you want, a pretty tensioner? Or one that works? What is more important, how a tensioner that you can hardly see looks? Or having maximum boost and not beating up your crankshaft/oil pump gears?

Your car comes with a 6 rib wide belt. A 6 rib system in conjunction with our Frankentensioer is enough to support up to 575rwhp. But, like anything sometimes you want more insurance. Or, you may have plans for more power in the future and you want to convert to 8 rib now.

You can convert your belt system over to an 8 rib system. It doesn’t sound like much, but it represents 33% more belt. That’s quite a jump.

And some would argue that a 8 rib belt looks cooler than a 6 rib.

Kit includes 12% overdrive ATI harmonic balancer. A good quality balancer is a key ingredient in all built motors. If a built motor is in your future or you want to treat your crankshaft and oil pump gears better a good balancer is never a bad idea. ATI is considered by most to be the “top dog” of harmonic balancers. The 12% overdrive (7.25”) size will give you more flexibility in the future if you want to spin a blower fast/hard. Because of the 12% overdrive the supercharger pulley that comes with this kit is larger (3.3”) to keep your blower speed the same. Because the supercharger pulley is larger you have more contact/traction. Which is never a bad thing.

Kit Includes:

The kit includes all of the pulleys you will need to convert to an 8 rib system. We include a clutched alternator pulley in this kit. They are about impossible to get, and if you can, they cost a fortune. We also include extra 76mm and 90mm idler pulleys so you can adjust/dial in your belt tension perfectly (see Frankentensioner instructions for details). All of the idler pulleys are Gates brand so you can be sure that you’re getting good quality bearings.

-ATI Superdamper 12% OD

-OEM power steering pulley

-OEM air conditioning pulley

-90mm idlers x3

-76mm idlers x5

-Clutched alternator pulley

-Supercharger pulley

Installing this kit requires the following special tools:

-Harmonic balancer puller

-Power steering puller/installer

-Alternator pulley “socket”

-Impact gun for alternator pulley socket

These tools can be purchased for not much money (except the impact gun). Or you can rent/borrow them from most auto parts stores.

If you purchase our “Bulletproof” Denso alternator it will come with your choice of pulley. In that case that choice would be 8 rib. It will already be installed so you won’t need the alternator pulley “socket” or an impact gun.

This kit is to be used with the purchase of our “Bulletproof” Denso alternator which already comes with your choice of pulley

Your car comes with a 6 rib wide belt. A 6 rib system in conjunction with our Frankentensioer is enough to support up to 575rwhp. But, like anything sometimes you want more insurance. Or, you may have plans for more power in the future and you want to convert to 8 rib now.

You can convert your belt system over to an 8 rib system. It doesn’t sound like much, but it represents 33% more belt. That’s quite a jump.

And some would argue that a 8 rib belt looks cooler than a 6 rib.

Kit includes 12% overdrive ATI harmonic balancer. A good quality balancer is a key ingredient in all built motors. If a built motor is in your future or you want to treat your crankshaft and oil pump gears better a good balancer is never a bad idea. ATI is considered by most to be the “top dog” of harmonic balancers. The 12% overdrive (7.25”) size will give you more flexibility in the future if you want to spin a blower fast/hard. Because of the 12% overdrive the supercharger pulley that comes with this kit is larger (3.3”) to keep your blower speed the same. Because the supercharger pulley is larger you have more contact/traction. Which is never a bad thing.

Kit Includes:

The kit includes all of the pulleys you will need to convert to an 8 rib system. We include extra 76mm and 90mm idler pulleys so you can adjust/dial in your belt tension perfectly (see Frankentensioner instructions for details). All of the idler pulleys are Gates brand so you can be sure that you’re getting good quality bearings.

This kit is to be used with the purchase of our “Bulletproof” Denso alternator which already comes with your choice of pulley.

-ATI Superdamper 12% OD

-OEM power steering pulley

-OEM air conditioning pulley

-90mm idlers x3

-76mm idlers x5

-Supercharger pulley

Installing this kit requires the following special tools:

-Harmonic balancer puller

-Power steering puller/installer

These tools can be purchased for not much money. Or you can rent/borrow them from most auto parts stores.

Your car comes with a 6 rib wide belt. A 6 rib system in conjunction with our Frankentensioer is enough to support up to 575rwhp. But, like anything sometimes you want more insurance. Or, you may have plans for more power in the future and you want to convert to 8 rib now.

You can convert your belt system over to an 8 rib system. It doesn’t sound like much, but it represents 33% more belt. That’s quite a jump.

And some would argue that a 8 rib belt looks cooler than a 6 rib.

And some would argue that a 8 rib belt looks cooler than a 6 rib.

Kit Includes:

The kit includes all of the pulleys you will need to convert to an 8 rib system. We include a clutched alternator pulley in this kit. They are about impossible to get, and if you can, they cost a fortune. We also include extra 76mm and 90mm idler pulleys so you can adjust/dial in your belt tension perfectly (see Frankentensioner instructions for details). All of the idler pulleys are Gates brand so you can be sure that you’re getting good quality bearings.

-OEM style harmonic balancer

-OEM power steering pulley

-OEM air conditioning pulley

-90mm idlers x3

-76mm idlers x5

-Clutched alternator pulley

-Supercharger pulley

Installing this kit requires the following special tools:

-Harmonic balancer puller

-Power steering puller/installer

-Alternator pulley “socket”

-Impact gun for alternator pulley socket

These tools can be purchased for not much money (except the impact gun). Or you can rent/borrow them from most auto parts stores.

If you purchase our “Bulletproof” Denso alternator it will come with your choice of pulley. In that case that choice would be 8 rib. It will already be installed so you won’t need the alternator pulley “socket” or an impact gun.

This kit is to be used with the purchase of our “Bulletproof” Denso alternator which already comes with your choice of pulley

Your car comes with a 6 rib wide belt. A 6 rib system in conjunction with our Frankentensioer is enough to support up to 575rwhp. But, like anything sometimes you want more insurance. Or, you may have plans for more power in the future and you want to convert to 8 rib now.

You can convert your belt system over to an 8 rib system. It doesn’t sound like much, but it represents 33% more belt. That’s quite a jump.

And some would argue that a 8 rib belt looks cooler than a 6 rib.

And some would argue that a 8 rib belt looks cooler than a 6 rib.

Kit Includes:

The kit includes all of the pulleys you will need to convert to an 8 rib system. We include extra 76mm and 90mm idler pulleys so you can adjust/dial in your belt tension perfectly (see Frankentensioner instructions for details). All of the idler pulleys are Gates brand so you can be sure that you’re getting good quality bearings.

This kit is to be used with the purchase of our “Bulletproof” Denso alternator which already comes with your choice of pulley.

-OEM style harmonic balancer

-OEM power steering pulley

-OEM air conditioning pulley

-90mm idlers x3

-76mm idlers x5

-Supercharger pulley

Installing this kit requires the following special tools:

-Harmonic balancer puller

-Power steering puller/installer

These tools can be purchased for not much money. Or you can rent/borrow them from most auto parts stores.