When you talk to gearheads about performance, often times that conversation is limited to the engine’s performance, with an occasional transmission or rearend thrown into the mix. When you build your engine for more performance, the rest of the drivetrain can become weaker links, and they need to be built or upgraded to handle the additional power and torque coming from the modified engine.
Throw the word driveshaft into those conversations, and it’s not really given much thought other than installing beefier universal joints. Is there such a thing as a performance driveshaft? Definitely, and one company that has introduced a new line of performance driveshafts is QA1. Its carbon fiber driveshaft line is one such performance driveshaft that is designed for street and racing enthusiasts who want more for their musclecar or race car.
Driveshafts are essentially made in three materials: steel, aluminum, and carbon fiber. As you can guess, a carbon fiber driveshaft is going to be the lightweight of the bunch, and a 48.5-inch driveshaft weighs in at just 7.2 pounds without the universal joints attached. A similar steel driveshaft can weigh as much as 40 pounds, while a similar aluminum driveshaft can be more than twice the weight of the carbon fiber shaft.
Why Carbon Fiber?
The first two things most people think about with carbon fiber are the weight savings and its most significant property, strength. But carbon fiber alone is not what makes it strong. The process of laying the fibers in a particular pattern is what provides the strength, and in the case of QA1’s driveshafts, the strength can be increased or decreased based on how the fibers are wound over the mandrel. Of course, the cost factor is going to be a primary concern, but who would be the target audience for a carbon fiber driveshaft?
For that answer, we turned to QA1’s Travis Gorsuch, who told us, “Our shafts are performance shafts and are typically used by people who are looking for increased performance. Sometimes that increase in performance is a higher critical speed due to a higher vehicle speed, sometimes it is an increase in torque capacity due to a power increase and sometimes the customer is looking for a better looking shaft to complement the high end look and attention to detail that they are going for.”
The driveshafts will work for both street and drag racing applications; Gorsuch suggests that the bottom line all depends on the individual customer and what their requirements are. People have been racing with steel and aluminum driveshafts for decades, so nobody is trying to reinvent the wheel here. They are, however, allowing that wheel to spin much faster than before.
Gorsuch said, “I am sure you remember when the stock Mustangs were having driveline issues due to the top speed being raised in the vehicles’ computer. Those are customers that can take advantage of our stronger, lighter driveshafts that have a much higher critical speed than steel or aluminum shafts.”
Things like fiber angle, resin properties, and length have a significant impact on the stiffness of the tube as well as wall thickness. -Travis Gorsuch
“In order to determine what wall thickness should be used, we establish design criteria like ultimate strength, torsional stiffness and critical speed. Once the design criteria are agreed upon, we run simulations and tests to determine the proper wind angles, material properties and wall thickness,” he said.
Higher Critical Speed
What is critical speed, and why is it significant? Rotating shafts will deflect during rotation, even a precision-balanced shaft will begin to deflect as it starts to reach higher speeds. The weight of the shaft and the amount of deflection creates a resonant vibration at certain speeds, this is known as critical speed. As this vibration occurs, it can put additional stress on the other components in a driveshaft – namely the universal joints – which can cause driveshaft failure.
A carbon fiber driveshaft with a lighter rotational weight and a higher critical speed can reduce that resonant vibration and provide better performance. “With conventional materials such as steel or aluminum, the torsional stiffness or amount of twist can be approximated by knowing the diameter and wall thickness. This is due to the materials having equal material properties in all directions,” Gorsuch said. “For composites, the material does not have equal properties in all directions. This makes it much more difficult to generalize the amount of twist by only knowing the diameter and wall thickness.”
Because QA1 can experiment with different angles when winding a carbon fiber driveshaft, it can affect the strength and also the weight. As Gorsuch describes in the video below, fiber is strong in one direction, so in order to make the driveshaft strong in several directions it is wound at specific angles to provide torsional strength, and to help achieve a higher critical speed. However, as the strength can be increased based on fiber angle, the critical speed can decrease. QA1 has experimented with the various angles that will impact the strength, stiffness, and the critical speed of the driveshaft.
Gorsuch said, “Each layer of fiber that is applied can have a unique angle so as you can imagine, there are nearly infinite combinations of fiber angles to use as the tube is being constructed. We have developed an advanced simulation method to help us to determine the best possible angles to use based on the design criteria. Once we have a handful of angle options, we make sample parts and test them to verify the results of the simulation.”
QA1 worked with 3M’s Aerospace and Transportation Group to develop a nano-silica matrix resin for its driveshafts. This resin provides the driveshaft with better abrasion resistance and helps to make the shaft much stronger. Gorsuch said, “Typically with resin systems you either have tough but flexible systems or the part is brittle and stiff. The new matrix resin gives us the best of both worlds: tough and stiff.”
The machines used to wind the driveshafts allow QA1 to build driveshafts up to 4.1 inches in diameter, and up to 12 feet in length. After the design is entered into the computer based on the customer requirements, the shaft is wound with up to 28,000 inches of fiber, each band can contain approximately 24,000 fibers in it. After the filament winding process, the driveshaft is placed in a custom oven and baked at temperatures above 300 degrees.
Finishing off each driveshaft is a billet yoke designed for the 1310 or 1350 Spicer universal joints, with the capability of handling up to 2,000 horsepower and 1,500 lb-ft of torque. The typical carbon fiber driveshafts are 3.2 inches and 3.7 inches with a wall thickness ranging between .080 inches and 0.125 inches. While most driveshafts need to be balanced, QA1 has worked hard to design the components to require very little balance correction. They do have a design area in the yoke where material can be removed, but Gorsuch says the finished driveshaft tpically requires very little correction to be within balance specifications.
Measuring The Driveshaft
It almost seems like measuring a driveshaft would be a simple task of taking the measurement from the tailshaft housing to the differential, but it does involve a little more than that single measurement. To make sure the driveshaft is the proper length, and does not bind up on the output shaft of the transmission, there needs to be some play for the slip yoke since the rear of the driveshaft is mounted solid to the differential.
This play in the slip yoke allows for the movement and articulation of the rear suspension, as well as the flexing that the body does while the car is cornering, or driving on uneven surfaces. As the suspension raises or lowers, the shaft will move in and out slightly, and that needs to be compensated for when measurements are taken. QA1 takes all of this into consideration and can send you the transmission yoke if you need it to help get your measurements.
QA1 offers an order form that customers can download from the website, illustrating where all measurements should be taken from. One critical measurement is the end of the tailshaft housing to the center of the rear universal joint. The slip yoke is long enough that the amount of play doesn’t have to be precise, but it does need to engage the splines on the output shaft with some play for that suspension articulation.
As you can imagine, without any play in the slip yoke serious damage to your transmission or differential can occur. This is also a good time to determine what universal joint size you will be using with your driveshaft, and QA1 can help you with that decision if you’re not sure which direction to go.
Is a carbon fiber driveshaft too much for a street machine? It’s not a matter of will it work in as much as it is an issue with your wallet. Prices are steep on carbon fiber no matter where you go, but as Gorsuch said earlier, it all depends on the requirements of the customer. You can find out more about QA1’s carbon fiber driveshafts in the two videos we’ve linked here, above and below, as well as checking out their website. The technical department is just a phone call away, and they can help get you connected to a driveshaft for your application.