Racing proves the weakest link of a chain will always break first. It’s part of going faster. Smart racers stay ahead of breakage by using products that strengthen those weak links. This is the case in Callies’ new splined crankshafts. Callies is already known for their bulletproof crankshafts and by them incorporating a spline on the snout, or post of the crank, have taken the next evolutionary step in making them even stronger.
The problems first surfaced in Top Fuel, Funny Car, and bigger classes in Tractor Pulling with their use of higher volume superchargers. Typically, these blowers are the largest in motorsports. Using them creates a problem where the torsionalload of the crank pulley exceeds the capabilities of standard keyed configurations for retaining a blower drive pulley on the crankshaft. Simply put, the bigger blowers were overpowering the keys and keyway mountings of the blower pulley on the crank. Pulleys in such applications are seeing the maximum amount of torque and those numbers are not going to get any smaller. So, how do you make the pulley/crank connection stronger to support such loads?
We first need to understand how crankshafts without a spline use a standard round post with two keys, set in their keyways, 180 degrees from each other. These keys are intended to provide alignment between the pulley and crank. The problem is they can only offer minimal resistance to rotational forces because the keys can only ‘hold’ the pulley with the totaled combined square inches of surface area of the keys and keyways. And as blowers put out more and more power, the loads on that connection are increased. As power increases, pulleys and belts get bigger and stronger, too. It all adds up to more force on keys and keyways.
Specifically, all the torsional forces directed to the keys center themselves on the keys and sides of the keyways. It’s much like the contact patch for tires. More contact can mean more traction for tires but in the keyways, it means more forces drilling down into those keyways. On top of that, keys and keyways are subjected to torsional forces in alternating directions as the crankshaft rotates. Half the time, the post is being turned downward 180 degrees. Then, as the crank rotates, it reverses the direction of the forces and is pushed upward 180 degrees. Inside the keyway, the forces are pushing the key back and forth in the keyway. If there is any slop in the keyway, these forces will increase any tolerances, furthering wear and slip on the blower drive pulley. In less than 10 runs, keys and keyways can begin the wear equals damage cycle.
The solution was to take that load off the keys and keyways and distribute it over the entire post area. Using a spline does just that, dispersing the load over 100% around the post. By comparison, the key system has only the square inches of the two keys and keyways to support the pulley while the spline, with typically 33 ‘teeth,’ covers the entire 360 degrees of the post.
The benefits of using a splined drive are numerous. One is the core strength of the post is now increased. Because of the use of surface area and its increased strength spread out over the entire diameter of the post, splines don’t need to penetrate as deep into the material of the crank post as much as typical keyways. Splined crankshafts provide an increase in cross section material between the bottom of the spline and the post bolt hole compared to a keyway. Not cutting as deeply into the post also maintains its strength and integrity better directly where it is needed on the post. And the flip side of that is not losing the material that is machined out for the depth of the keyway. In fact, the post on a splined crankshaft is bigger than those without splines. So along with being stronger in design, the added post material provides even more strength over using the key method.
In effect, the bonus to using a splined crankshaft is threefold. One is using the surface area to disperse the load of the blower drive pulley. Two, a stronger post to also support that critical load point. And three, the weight of the crankshaft (and resulting rotating mass) is kept to a minimum while strength is not compromised. And any help the post gets in being stronger and living longer translates to the crankshaft doing the same.
All these factors combine so the spline will outlive the crankshaft in these typical bigger blower applications. That’s because in the example of a Top Fuel engine,the crankshaft will be removed from service due to torsional fatigue before the splines show cause for concern.
What little differences there are between splined and non-splined crankshafts comes down to only the post itself. For one, the post diameter is increased .175 inch for the equivalent of the Big Block Mopar, the standard size in those bigger blower configurations. Crankshafts with splined posts require using specific accessory components that vary by application. These would be the pulleys used on the crankshafts, insuring mating splines and sizes are used. It’s more about matching the blower drive components to the spline and vice versa.
Nothing else changes when using a splined crankshaft. The crank timing gear is still installed and removed the normal way. The balancer also is installed/removed the usual way. The same timing chain covers are still applicable.
Staying ahead of weak links, all Callies splined post crankshafts are manufactured from billet steel. Splines are not found on forged cranks as forgings don’t have sufficient material on the front end and post where splines are machined. Callies uses 100% quality-certified American steel on their Ultra Billet splined crankshafts; available in a variety of strokes. Using the billet option also allows the opportunity to select from a wider variety of materials; further fine tuning each engine’s application.
Using a splined crankshaft also allows racers to ‘strengthen’ their engines even if they aren’t running the higher volume superchargers. This can add reliability and product longevity to their engines. In short, if you can run an engine competitively with less stress, stronger parts and assemblies should last longer.
Down the line, as engines not using the higher volume superchargers evolve, they, too, may need the safety and reliability of a splined crankshafts. For engine shops, it will be an easy upsell. Include a stronger, splined crank in a build and a racer won’t need to worry about a shorter life of their crank due to the pulley connection. Most racers will buy into stronger and longer wearing in a heartbeat and those on the edge of needing a splined drive will smartly make the jump.
Story by John Carollo