Allmond Marine gives Seminar at 2019 PRI Show
In December of 2019, I was honored to present to a standing room only crowd at the Performance Racing Industry Tradeshow. I was asked to speak on the topic of valvetrain performance specific to offshore powerboats, and this was likely the first time this topic had been discussed publicly ever! To say the least, I was honored. The following is a synopsis of my talk.
What Is Frequency?
Designing a valvetrain starts with a characteristic that few engine professionals discuss, or have the ability to discuss intelligently: system natural frequency. But what is frequency anyway?
Frequency is part of what engine guys mean when they say things like “valvetrain stability” or “valve float”. Getting the frequency wrong can lead to instability or “valve float” (which is itself such an abstract term I don’t like using it myself, but I digress). Frequency is the rate that an object vibrates. In an engine, this vibration rate is very important, as it is a major factor in establishing the redline of your engine. So how should you establish a frequency target? One method is to look at the acceleration of your cam profile (contact Allmond Marine if you want to do this), but a quick and dirty way is to use what I call the “Rule of 5 ½”.
The Rule of 5 ½
If you’re lacking the assistance of a professional valvetrain engineer (ahem, call us!), you can use the equation above to calculate your valvetrain frequency target. The result is frequency expressed in Hertz, or cycles per second. For example, if your max engine speed is 6200 rpm, plugging that into the equation above gives you 568Hz. This is a safe value that should cover you for some of the most aggressive profiles in existence for the Big Block Chevy. 99% of the profiles in use will respond favorably to a 568Hz valvetrain connected to them at 6200rpm.
Of course, the use of this rule of thumb will (as we’ll find out later) lead you to build a system that is much stiffer and lighter than the guy in the slip next to you. That could be for a few reasons:
- His engines were built without the help of his own valvetrain professional
- His engines are using a cam profile designed for 1980’s valvetrain technology
- He’s willing to accept 200-250hr service intervals, replacing rockers, springs and lifters on a timetable
- He just doesn’t care as much as you do!
Finally, what if what it takes to achieve this 568Hz minimum target is outside of your budget? No worries, Allmond Marine can help you select a cam with a lower frequency requirement. The tradeoff is lower performance, but sometimes that’s what it takes to get you the durability you want. Allmond Marine can help you build a valvetrain that complements your cam, so you spend your time on the water and off the service rack.
