Valvesprings provide the force that keeps the valvetrain together, which is a good thing in offshore performance boats.
But how does one decide on the spring design he needs? Most people will ask the cam company they buy the cam from. They’ll get an answer, usually based on what has worked in the past. This is the way it has been for the past 25 years. That’s right, people are still using the same basic designs that have been around since 1995.
But what makes a spring design right for the Chevy big block? Well first, it needs to have the right open load. A quick calculation assuming typical valvetrain masses for the BBC, a reasonable cam profile of .700″ lift and a peak engine speed of 6200rpm comes up with something around 550lb force. If your application is slightly heavier, you turn more rpm, or your profile is more aggressive, you might need slightly more open load. If you have a softer profile, lighter weight parts or turn less rpm, you would need slightly less.
This is where it gets dicey – the seated load. Some people will tell you that there is a “magic” seated force number, or one that you don’t want to go below. The real truth is it’s much more complicated than that. The fact is that it can be done with much less seated load than you think – around 160lb is not out of the question with the right design, the right valvetrain and a well-designed cam. The caveat is it must all be designed to work together. This does not consider turbocharging, mind you: sizing springs for those engines is beyond the scope of this article.
Read the next article where we will explore valvespring vibration and spring surge as applied in offshore performance boats.
