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January 28, 2022 7 min read

Picture this, you buy a car and it has a supercharger on it and you know that the first thing you are going to do is want to make more power right?Not a box tune and an intake kind of power level, you want to go further. Easy solution, put a pulley on it. Despite you are already getting nagged at by your wife for spending money that was supposed to go into finishing the basement, you hit up trusty google. You find yourself at a standstill wondering why you have to choose a pulley that reviews say slip sometime after they get worn down, or that they completely destroy belts. That is where we found ourselves for years just like everyone else. 

Once the return of the GT500 was announced in 2020, we knew that after years of dealing with belt slip issues on other cars with other pulley options this would be a fantastic time to do what we do best here at SPE, make it better. The big goal in mind was for the least amount of slip while keeping belt wear as low as possible, all in the lightest set up we could come up with. We knew it would be a hard balance to find, so what would be the top priority? 

Priority was given to belt slip issues commonly dealt with by almost anyone from aggressive setups with small pulleys on their cars, even stock pulleys have issues with belt slip. Obviously there would be many options to have an extremely rough surface to grip the belt so that it would not slip under any load. But at what cost would you have for a surface like that? On the contrary, having a surface that minimized belt wear would not provide enough grip, especially when dropping down in pulley size significantly from factory configuration. Factoring in the rotational mass of the pulley also makes a difference in how the belt and the pulley interact while under different loads and how the load is applied. Just three things to take into consideration, sounds simple right? Well, why was there not a lightweight pulley system that had a lot of grip with minimizing belt wear out on the market for everyone to buy? Personally I believe that everyone was settling, thinking “ If it isn’t broken why fix it?”. Now technically the pulley systems offered worked, but how well did they work? What did you have to sacrifice? Can it be done better?


Pulley Grip Test Chart


After countless hours of testing and development on our GT500 test cars and more recently our Hellcat Durango ( Click Here To Check Out SPE Hellcat Selection ) we ended at our patent pending Convex Knurling Process (CKP). Taking the process of knurling that often people overlook for its ability to have substantial increase in friction on a surface that would otherwise be slippery, and adapting it to our automotive needs we hit the sweet spot we were looking for. For those of you that are not familiar with knurling, it is a process in which material is removed or displaced by either hand or machine to create a patterned textured surface, usually in the diamond pattern found commonly on gym weights and handles of tools. ( Click Here To Lean More ) A unique property about knurling is the amount of friction is dependent on the amount of force applied to the surface. Taking this concept and adapting it to our needs for pulleys we were able to create a surface that provided minimal belt wear at low load, and as load is applied the friction increases virtually eliminating belt slip.

Once the CKP process, as briefly described above, was finalized in theory and in CAD there began the long hours of prototypes and testing. Surely there would be many ways to adapt a knurled surface to the face of a pulley, but which made the most sense? Based on the example made earlier, one of the most everyday types of knurling is found on the handles of gym weights and tools. Imagining the pulley sitting on your supercharger in your hand, and you try to spin it while gripping it as tight as you could. What is going to happen? It will spin in your hand, imagine what will happen when you are leaving the line while having some fun down in Mexico.

Taking our product testing to a new level we developed a process in which we make a mock set up of the belt drive set up on a steel plate in order to test out the pulleys on each vehicle platform that we make the pulleys for. Consisting of the crank pulley, tensioner, supercharger pulley, and any accessory drives that may be present on the vehicles, we position them in factory locations and route the belts through the pulleys and lock the belt out on the stationary crank pulley with full tension applied from the tensioner. Then using a digital Snap-On torque wrench we then spin the pulley through a full 180 degree sweep, whilst eventually making the pulley slip the wrench records max torque applied until slip occurred which is then read and recorded. This is our testing method for all of our pulleys, as well as when stacking our CKP pulleys up against competitors. Keeping the testing methods, and ideals consistent across the board for the most accurate results possible. Below is our YouTube video giving a very in depth overview from Dan Snyder of our GT500 pulley line, CKP process, and how we test these pulleys.



Taking pulley size into consideration our pulleys do not run exactly true to listed size to keep boost increase scalable from factory levels. Meaning the change from actual factory size is in .100” increments to keep an even 1psi change in boost (condition depending such as altitude) when changing pulley sizes. This is how we found it to be easiest to keep a constant boost level increase relative to factory levels without too much added confusion. Our GT500 pulley line currently ranges from 2.27” all the way up to 3.2” for those of you that either want to push a stock blower to the limit or to take some boost and heat out of the car for autocross or similar racing applications. Also offering pulley setups for Helllcat platforms, as well as Whipple and Roush blowers currently with plans in the works currently for expanding into GM vehicles such as the Camaro as well. 

The unspoken hero of this whole operation is the hub and tool that was developed to hold these amazing pulleys to the supercharger. Being able to take the massive stock pulley off of the GT500 and replace it with the lightweight hub assembly and pulley from SPE Motorsport is the best way to take rotational mass off of the blower snout and improve the performance of the car. Not to mention the process is very easy to accomplish even for the weekend warrior. The hub is available in either stainless steel or titanium for the most amount of weight removed possible. Utilizing the hub tool that we developed there were substantial weight savings on the design of the hub compared to others on the market. To hold the pulley onto the hub, we offer different options for hardware. You can choose between stainless steel or colored titanium to add a little something extra to under the hood of your vehicle. The complete package saves weight thus reducing the wear on your supercharger and engine over time, not to mention the reduction of rotational mass that your engine has to spin will also aid in reducing belt slip and making the supercharger more efficient. 

Taking the same concept of bolt on and go installation, we offer either an adjustable or fixed idler pulley for vehicle setups that would benefit from having the option to add it to the set up. Currently offering these for the 20+ GT500 only, but not out of the question for other platforms as the testing or demand shows need to add to our product line. The fixed idler is a great option for someone that does not plan on changing their pulley set up very often or ever at all. Just a one and done upgrade to your new or current set up. The adjustable idler features the same easy installation with the added range of adjustment needed for switching pulley and belt sizes simply and effectively. Not to mention being able to dial in your belt wrap on the supercharger pulley more than a fixed idler or none at all. Perfect options for anyone and any set up. 

After not even a year of having our pulleys on the market for everyone to enjoy, we have hundreds upon hundreds of our pulley and idler kits out there on customers' cars. Installed by many shops professionally like our friends over at Palm Beach Dyno! Some people do it themselves and some get their cars done at various shops across the country and even on different continents. People all over the world enjoy our products on a daily basis, and that is the fuel that keeps us going.

Taking all of this into consideration I would encourage you to take the time to go check out our YouTube channel and hear the details from Dan himself. I can give you all of the nitty gritty information you would want in a blog or an email, but being able to watch a video and see the quality of the parts, see the testing method, and hear the passion that Dan has for making all of the products that we sell truly is a great reassurance that we strive to give the customers the best that we can. There is a TON of great information there in an easy and interesting way to learn more about a variety of products that we sell.

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