In the realm of automotive engineering, few components are as crucial to engine performance as the camshaft. Whether you’re a seasoned engine builder or a racing enthusiast, understanding the intricacies of camshaft design can mean the difference between victory and defeat on the race course. In this comprehensive guide, we’ll explore the advanced science behind building winning camshafts for marine racing engines, delving into the expertise of leading manufacturers to uncover the secrets behind their success.
Deciphering the Camshaft Catalog
Flipping through a camshaft catalog can be an overwhelming experience for many. Rows of data detailing lift, duration, lobe split, and more can leave even seasoned enthusiasts feeling lost. However, beneath these numbers lies a world of precision engineering and meticulous design that shapes the performance of race-winning engines.
Experienced engine builders and camshaft designers understand that these numbers only scratch the surface of what makes a camshaft effective on the racecourse. Modern camshaft design goes far beyond simple lift and duration, with engineers meticulously analyzing every aspect of valve motion to optimize engine performance.
Beyond Basic Specifications: The Anatomy of a Winning Camshaft
To gain insight into the complex process of camshaft design, we turn to a leading valvetrain engineer renowned for his expertise in the field. By asking a simple question—”Beyond basic lift and duration, what goes into designing a camshaft capable of winning races, or running hundreds of hours in a performance powerboat?”—we uncover a wealth of knowledge and expertise.
1. Communicate, communicate, communicate
Just as effective communication is essential in any relationship, it plays a pivotal role in the collaborative process of designing a winning camshaft. Chris Allmond of Allmond Marine emphasizes the importance of understanding the specific needs and preferences of racers and engine builders. “Factors such as desired torque characteristics, previous camshaft experiences, and cylinder head specifications all influence the design process. When coming up with profile proposals, we sometimes like to reverse engineer the camshaft the customer is running, if it isn’t one of ours. This allows us to gain insight on how the profiles might perform, in both airflow and dynamic characteristics,” highlighting the importance of clear and open communication between engineers and customers.
2. Lose on the Dyno, Win on the Water
While big torque figures may garner attention, smart engine builders and cam designers know that the cam that is best for a racecar isn’t the best choice for a performance boat. Chris Allmond highlights the need to tailor camshaft characteristics to suit the demands of the marine environment. “First, we need to establish how the customer’s exhaust is designed – especially where in the system the water mixes. This presents a significant limitation on our design.” He goes on to explain the dynamics of water reversion, “with high levels of overlap, water can work its way up the exhaust pipe and into the cylinder – which is never a good thing. The further away from the riser the water is introduced into the exhaust stream, the better your camshaft options become.” He then explained how camshaft selection can benefit things like drive life, “performance marine engines tend to be big on displacement. With camshafts that have been typical over the past 30-40 years, the engines that many boats have can easily overpower a Bravo drive, even with straight-cut gears. They can’t handle the torque. Think about it this way – torque breaks drives, while horsepower tends to overheat them. Through modifying the valve events, we can bleed off some of the torque of your engine while retaining the power up top, where you’re hitting your max speed numbers.”
3. The Cam Doesn’t Matter (Or Does It?)
Okay, we gotcha with that headline. The truth is that the engine cares about where the valve events occur, and how much area there is under the lift curve. Chris stresses the importance of understanding the fundamental principles of valve timing and motion. “By focusing on key parameters such as rpm limits, valvetrain mass, displacement, bore/stroke ratio, rod ratio and cylinder head flow, we can optimize valve events to extract maximum performance from the engine.”
4. Rocker Ratio and Lobe Design
The relationship between rocker arm ratios and camshaft design plays a crucial role in determining valvetrain dynamics. Chris explains, “rocker ratio should be used as a tool in the box. For example, NASCAR engines prior to 2015 had to run flat tappet lifters. This limited the velocity which could be ground into the camshaft. To increase valve velocity, teams were running ratios over 2.0:1 – the highest I saw was 2.4:1. Doing this makes the stiffness of the rocker and everything on the cam side of it very important. With today’s roller lifters, the same valve velocity is achievable with a 1.95:1 ratio, and stiffness isn’t quite as critical.” By leveraging the lever-like properties of rocker arms and carefully crafting camshaft profiles, engineers can fine-tune valvetrain behavior for optimal performance.
5. Compression Ratio vs Dynamic Compression
Understanding the distinction between static compression ratio and dynamic compression is essential for optimizing engine performance. Chris discusses how camshaft design influences dynamic compression, or cranking pressure, by controlling valve timing events: “Cranking compression is a function of intake valve closing angle and static compression ratio. Cranking compression is positively associated with torque – as cranking compression rises, as does torque, until the fuel autoignites. Pump gas has a relatively low cranking compression tolerance, while methanol can tolerate over 300psi in drag race applications. Shorter duration cams tend to close the intake valve earlier, and advancing the cam does this as well. Long duration cams have the downside of not being able to generate much combusion pressure at low speeds, hurting torque.” By aligning intake valve closure with piston motion, engineers can optimize cylinder pressure for maximum torque output across the rpm range.
6. The Four Pattern Cam
Most cams today have two profiles: intake and exhaust. Multi pattern camshafts showcase the evolving landscape of camshaft design technology. By incorporating distinct lobes for inner and outer intake runners, these cams optimize the valve events to intake tuning characteristics in multi-cylinder, single throttle body engines. Chris explains, “with a common single plane intake, the middle runners have a shorter length than the outer runners. This makes a camshaft with only one intake lobe a compromise of the two. By making the center cylinders a degree or two longer, and the outer runners a degree or two shorter, we can align the valve events more closely to where the intake runners want to tune. This gives us the benefit of putting more area under the horsepower curve.”
7. Fighting Harmonics
Harmonic resonance presents a significant challenge in camshaft design, particularly in high-revving race engines. Chris highlights the importance of working around spring harmonics to prevent valvetrain instability and potential engine damage. “There are things that can be done to damp valvespring vibration, but they are limited. Ultimately, if you want your engine to run well dynamically, you’ll have to make sure your camshaft complements your springs. To aid in that, we’ve developed a tool to help our customers get their bearings on what spring will likely work with their cam. That’s unique to the industry, and is only available through us.” Through careful lobe design and component selection, engineers can minimize the effects of resonance and maintain valvetrain stability under the most demanding conditions.
Conclusion
The world of camshaft design is a complex and dynamic landscape, where precision engineering meets real-world performance demands. By delving into the insights of leading manufacturers and engineers, we’ve gained a deeper understanding of the science behind winning camshaft design. From communication and collaboration to innovation and optimization, every aspect of the design process contributes to the ultimate goal: victory on the racetrack. Whether you’re a racer, engine builder, or enthusiast, the pursuit of excellence in camshaft design continues to push the boundaries of automotive engineering and performance.
