Building an engine is more than just assembling a bunch of parts to the correct tolerances and torque specifications, everything has to be matched together for the application. The valvetrain is one of the areas where properly matched parts are vital to ensure that the engine functions properly and the valvesprings are the key to this. We talked with Nolan Jamora from ISKY Racing Cams about valve spring pressure and what you need to know when selecting your springs.
Having an understanding of what a valvespring is other than some coiled metal wire is important to helping grasp what its role is within the valvetrain. The valvespring is one of the most important parts of the combustion process and is the backbone of the valvetrain itself. Knowing what correct valvespring pressure is will help in the selection of the correct valvesprings so you get the most out of your engine and prevent catastrophic valvetrain failure.
A valvespring by itself really isn’t that complex of a component, it’s a spring that has the task of either holding a valve open or closed during the combustion process inside the cylinder. It also has to make sure the lifter stays in contact with the camshaft in most applications as the engine operates. The valve spring helps to make sure that all the fuel and air enter and leave the combustion chamber on time, much like a conductor of a train makes sure it leaves or arrives at the station when scheduled.
When you examine a valve spring it looks like it might be made of just an average metal material that’s wound into the desired shape. The truth is a lot of thought goes into what the springs are made of. According to Jamora, valve springs are made of a specific recipe of materials and are processed with care.
“The base material is iron mixed with several other metals such as chrome silicon, nickel, vanadium, and even titanium. We use a super clean material that allows us to start with a spring that has close to zero surface inclusions or imperfections. This material then goes through special processes as it is coiled. We also employ a micro polishing to the wire that eliminates any surface problems that may lead to failure. We also shot peen or nitride certain spring series.”
How a valve spring functions under load is what makes it so essential in how an engine operates, even more so as the RPM starts to climb. Jamora beautifully breaks down what the job of the valvespring is and how it functions within the valvetrain.
“A valve spring is the barn door of the engine really, its main job is to keep that valve opening, closing and seating just as the cam design intends it to. It must try to keep the valve motion as close to the cam design as possible. Because an engine is basically an air pump, the more air and fuel that can enter the combustion chamber and the higher the RPM it can run, the higher the power output. In the past, the weak link was always the springs, but in the last few years the springs have improved.”
Valve Spring Pressure
There are many abstract theories and ideas that can be difficult to understand if you’re trying to select parts for an engine build, valve spring pressure isn’t one of those measurements. Simply put, valve spring pressure is how much pressure is on the valve at a specific measurement. Part of what goes into this is what the spring’s rate is per inch and the installed height.
The valve spring pressure measurements you will see are what it has for seat pressure and open pressure. Seat pressure comes from the load that is placed on a valve when it’s seated in the closed position. Open pressure is how much load is on a valve when it’s at the highest open point and it’s being forced to close.
Selecting valvetrain parts is more than just putting a kit in a shopping cart on a web page, you need to make sure the valve spring pressure for the application is correct. The valve spring pressure helps to set the tone of how stable everything will be within the valvetrain, and when you have parts spinning at high RPM levels you’re going to need all the stability you can get.
“The job of the valve spring is to keep the valvetrain stable so that the valve motion follows the intended cam design for optimum horsepower. As the engine runs higher RPM levels and more aggressive cam designs, this becomes harder and harder for the springs. They can go into a spring surge, which results in valve float or the springs will just break. If you just picture the environment the valvetrain goes through, it’s almost a miracle the stuff survives,” Jamora explains.
Spring pressure needs to be different for various cams and lifters because the different materials require different spring loads so they are able to last.
Valvespring pressure has a far-reaching effect across the entire valvetrain. Since the springs are what helps control the show, they will have an impact on other parts like the camshaft and lifters. The spring has to be a match for the engine application’s RPM levels, whether that’s a high-winding naturally aspirated engine or one with a power-adder in play. You also have to take into account if a hydraulic, solid flat tappet, or solid roller camshaft and lifter package will be in use.
“Can a valvetrain ever be too stable…no. But can a valvetrain ever have too much spring pressure…yes, definitely. A normal flat tappet cam core is limited to about 145-155 pounds seat and 400-pounds open pressure. The simple reason is the material; cast iron cannot stand more pressure and will go flat. It cannot handle the same pressures as a roller cam, which is made out of steel. The correct spring pressure will ensure that the cam and lifters will last a long time and produce the desired effect,” Jamora explains.
Common Valve Spring Pressure Questions
Finding the correct valve spring pressure solution isn’t something that comes in a simple one size fits all package. According to Jamora, to get the correct valve spring pressure you need to decide what type of cam is required and what the application of the engine will be first.
“Here’s an example of what you need to consider when selecting valve springs. Let’s say you have a naturally aspirated engine with a hydraulic or solid flat tappet set up. It would run 125-145lbs on the seat and 300-400lbs open depending on RPM range and type of use, such as a street car or oval track racer. A hydraulic roller with a stock-style lifter would run 135 pounds of seat and 300-350 pounds open. A hydraulic roller, using our Hpx lifters designed in conjunction with partners Johnson Lifters in Michigan, can run 185 pounds seat and 535-pounds open. And our bushing hydraulic rollers run 200 pounds seat and 550 pounds open.”
As you can see there’s a big difference between the hydraulic rollers in this example, that comes down to the application for each.
“When you upgrade the lifter and the pressures they allow, you can run more aggressive cams. This is needed for a stable valvetrain in turbocharged, blown, and nitrous applications. If you attempt to run a boosted setup with the extra spring pressure needed without changing the lifters, the hydraulic mechanism will collapse and result in catastrophic failure,” Jamora explains.
The goal as always is valvetrain stability at high RPM while keeping the frictional losses to a minimum, which does rob horsepower.
What about if you’re building an engine based around a power-adder? If you’re going to spray some nitrous you won’t have to use anything exotic when it comes to valvesprings and valvespring pressure. You just need to make sure the valve spring pressure addresses the engine’s RPM and application needs. Now, if you plan on pushing a lot of boost into your engine, things get a little more complicated when it comes to valve spring pressures.
“In a boosted application with very high boost numbers, you should take into consideration that the backside of the inlet valve is under constant static pressure, which does indeed diminish the seat pressure. The question is, how much does it diminish and do I really need to seriously consider it in my valve spring choice? Let’s say you have a typical valve diameter of 2-inches, which works out to three-square inches of area on the backside. If you have a spring that has 300-pounds of seat pressure, a good rule of thumb is to deduct 10-pounds per square inch, which equates to 30-pounds maximum load at RPM. This brings the seat pressure down to 270 pounds,” Jamora explains.
So, when it comes down to it, how do you pick the correct valvespring that has the right pressure for your application? There are a few parts that go into this process, including talking with camshaft manufactures so you can talk about your camshaft selection and how it will interact with all the valvetrain parts you want to use. Jamora also has some words of wisdom to help you select the right valvesprings.
“The goal is efficiency, not effectiveness. What I mean by that is you can always throw a ton of spring pressure at a combo that has been having spring problems and the solution can be effective, but having needless extra spring pressure does cost horsepower. It’s better to understand the dynamics of a combo and chose a spring around that. While we need heavy pressures on the open side to keep the lifter on the cam and return the valve to the seat, the real stress to the valvetrain is the offset load flex during the wind up of the cam.”
Jamora also adds, “The load on the parts is at its highest off the seat as the valve opens and sends a shockwave to the pushrods and the rest of the valvetrain. If you can reduce seat pressure while keeping the system in a controlled state as well as keeping the frictional losses at a minimum then you are at your most efficient.”
As you can see, selecting the right valve springs with the correct amount of pressure takes a bit of research. By taking the time to get a set of springs that is matched to the rest of your valvetrain and your application, the possibility of valve spring failure is greatly reduced.