Part 1 – Camshafts, Lifters and Springs
We know, valvetrain selection is about as broad a topic as you can get in engine building, but it is an important topic that involves a number of different, critical components. These components – camshafts, valves, valve springs, lifters, rocker arms, and pushrods – all work in conjunction to allow air or the air/fuel mixture in and exhaust gases out of the engine, and the selection process for the proper parts can be complex. There are often more variables than a science project gone wrong, but valvetrain selection can also be boiled down to a few simple facets that if followed, can greatly help your selection process and keep your engine out of failure trouble. In part 1 of this article, we look at cams, lifters and springs.
Application, Application, Application
Depending on what you’re getting into, the application and your goals really dictate what the valvetrain hardware needs to be.
“I can’t stress enough application, application, application,” says Mitchell Wilson of Engineered Performance. “We have to look at whether the application is going to be turbocharged or not and whether it’s for drag racing or endurance racing. Turbocharged engines versus naturally aspirated engines are so polar opposite in regards to what they need to run properly and efficiently. We look at the application and determine a camshaft first. Then we can dial in what we want.”
Jared Alderson, of Kill Devil Diesel, agrees that valvetrain selection begins by understanding the engine’s intended use. On the diesel side, guys often want 1,000-horsepower grocery getters that get 20 mpg and can also tow the camper.
“It’s hard to check all those boxes,” Alderson says. “But you have to focus on the camshaft all the way through the valve springs and retainers, etc. On the diesel side, the valvetrain stuff is not discussed as much because they’re relatively low-rpm engines. The push for us has been to try and raise the power band.
“Diesels will make 2,000 ft.-lbs. of torque at 2,000 rpm, which is great, really drivable, really usable power, but also tends to push the crankshaft out of the bottom of the engine. In trying to make the engine survive, we’re trying to shift the power band up higher in the rpm range, which then takes the stress from the bottom end and shifts the stress to the valvetrain.”
While engine builders will want to start their selection process using application to dictate what they need, component manufacturers ask those same questions when supplying product information.
“The biggest thing is knowing the application and knowing where the application is going to go in the future,” says Bob McDonald of Jesel. “A lot of people, when they’re selecting parts, look at price, but they don’t really look at what they should be using or where their motor is going to end up in a year from now.
“We try to get someone into something that’s not only good for now, but it’s good for how their motor is going to evolve over the next couple of years. Right now, it might just be this small lift, naturally aspirated motor, but two years from now, it could have big lift with a nitrous kit on it.”
Where your engine could end up down the road is a very valid point, especially when you consider how long some engine platforms can run for.
“If the application has a long lifespan – SBC, Series 60, 6.0L Powerstroke, etc. ¬– the choices will vary depending on the engine variations,” says Adrian Long of QualCast. “The longer the lifespan, the more choices that will be out there simply because of tweaks the OEs have made.”
The LS engine platform is a great example of how far an engine can go over the years, especially when you consider what today’s engine builders and the components available are capable of.
“The LS market has turned into ‘stock’ engines making 1,500 horsepower with some boost and the perception is that they don’t necessarily require anything,” Alderson says. “What a lot of guys are finding is that to really take that 1,000-horsepower junkyard combo and turn it into a safer 1,000-horsepower combo that lasts more than a few passes, you do get into the valvetrain.”
An engine’s valvetrain needs to be looked at as a package, and there’s no better place to start than with the camshaft design. Selecting the proper cam profile is a key factor in assisting the engine in achieving the performance goals it has.
“Our biggest concern with what we’re trying to do is valve spring and camshaft selection,” Wilson says. “How much air is that cam going to allow for the cylinder head and how good is that valve spring going to be in the envelope of what we’re trying to achieve? Are we going to have proper response?”
When it comes to cams, it’s more an exercise in theory than a set formula where everyone can plug in numbers and magically get a cam that works for them.
“With turbocharged applications, a lot of people think bigger is better because we are making a huge amount of power,” Wilson says. “That does ring true on some applications where you’re full on drag and the engine lives at 5,000 to 10,000 rpm, which is a huge amount of rpm. The engine is going to have to see a lot of valve spring pressure and a lot of cam to let that engine breathe at the higher rpm.
“The other side of that coin is turbocharged engines making 800 to 1,000 horsepower for road course applications. With a turbocharged application, there is an instance where you end up going into a reversion effect because you’ve got too much cam and you’ll overfill the cylinder and start getting reversion back into the intake, which drops performance. In instances like that, turbocharged engines don’t necessarily want a huge amount of duration through a normal rev range (3,000 to 7,000 rpm). They’re looking for more lift. You’re trying to get air flow in and out as fast as possible.”
Most of what Engineered Performance works on are Nissan engines, which feature dual overhead cams. In those applications, base circle is a huge thing when it comes to properly setting up valve motion control with springs and cams.
“A lot of people are regrinding camshafts, and there’s nothing wrong with that as long as you’re taking the required steps to combat those differences,” Wilson says. “We have camshafts on the market that have up to 3mm reduced base circle. If their stock base circle is 32mm and you go down to a 29mm, that means the overall width of the base circle of the cam has reduced that much. If that’s the case, if you’re still running a stock length valve and you’ve reduced it 3mm, you have to somehow make up that difference.
“Some people think they can just sync the valve job. Well, that’s bad because you start reducing the material integrity of the valve seat and then you run into a whole bunch of issues there. You’ve likely already bought upgraded valves, but now you need a longer valve because the cam is ground down to a reduced base circle. No one wants to have to buy another set of $500 valves. That’s why we try to focus really hard on maintaining base circle because that maintains preload to your hydraulic lifters. That keeps optimum lift and valve motion control in check because you’re still maintaining the stock parameter, and you’ll quiet down your valvetrain because you have that constant preload at a preset clearance of lash.”
The second you start reducing the base circle, you get into what Engineered Performance refers to as a hockey puck situation.
“You’re taking a cam lobe, rotating it over on the max lift, and the second you’re on that really tight apex on the lobe, the lobe shifts over from open to closed,” he says. “On that closing end, the cam shutters. When it shutters, everything starts going away and you start running into a list of problems. We try to maintain everything as much as we can with a stock base circle and develop our cam profiles. Any good camshaft manufacturer that produces race cams will tell you the exact same thing if it’s an overhead cam.”
Just as gas engine builders are looking for the right amount of response from the camshaft design, so too are the diesel folks. However, the diesel world isn’t looking for lift as much as it’s about valve timing events.
“People want a truck that does everything,” Alderson says. “They want response, so the cam profile and valve timing events aren’t so much about lift like it is in the gas world. We’ve found that it’s more relevant to the valve timing events. Because diesels aren’t throttled, camshaft changes don’t give them the chop at idle like a gas engine does where you have the air/fuel mixture sloshing through the intake. Diesels are direct injected and because they’re not really throttled you can run a fairly large cam without really affecting idle quality.
“With our street-based camshafts, we try to keep the intake center lines fairly advanced, so you still keep lower rpm efficiency and torque production. On the higher horsepower stuff, to shift the power curve up similar to the gas world, we’ll run a later intake center line, but usually with higher durations a later center line definitely requires valve reliefs.
“The potential downside of that is the valve reliefs take away from the compression ratio, which on a race engine we would do intentionally to knock some compression out of it so it doesn’t hammer the pin bores and bushings as much so you survive for a few seasons at about 1,200 horsepower. For a street engine, you don’t want to have a 14:1 or 15:1 compression engine. A lot of street customers don’t want it to smoke or haze at idle, so keeping all the drivability in line is a balancing act, like everything else.”
In the diesel world, what is considered a bigger cam is still pretty mild compared to the gas engine stuff. Kill Devil Diesel’s Stage 2 cams for the 6.0L and 6.4L Powerstrokes are 180 degrees at .050˝, which is not much more than a stock LS cam would be.
“With diesel engines, you have to trap a certain amount of cylinder pressure in the cylinder in terms of valve timing events,” Alderson says. “Some of the big, big cams are harder to start and it might be a 16:1 or 17:1 compression ratio. Even on some of the competition engines we’ve done, the cam ends up being in the 230-240 at .050˝ duration range, and they still may be harder to start because you’re bleeding off more cylinder pressure.”
Once a camshaft is selected for your application, the next logical step is to look at what type of lifters will work best.
“A stock lifter can be suitable for many cam lobe profiles, valve spring pressures and engine speeds,” says Cale Risinger, technical sales manager at Melling. “But, for high-revving engines with aggressive cam profiles and high valve spring pressures, a performance flat tappet or roller lifter will be more suitable. Performance flat tappet and roller lifters have upgraded features designed to improve performance and durability.”
Lifters are a very big part of the valvetrain and its proper function. However, it’s a part that gets overlooked and that’s one reason a company like Jesel got into the lifter business.
“Because lifters can cause $2,000 of damage to the block, Dan Jesel decided that we’re going to build a spare-no-expense lifter, because we don’t want to have a lifter failure,” McDonald says. “A lot of people have a hard time with the prices of our lifters, but you’re getting what you paid for. It’s the highest-grade quality piece that we can produce with what’s available to us. Not every customer has that need, so we do have step downs.
“We have our tie bar lifter, which is kind of our entry level. We have our dog bone lifter, which is phasing out since its older technology. Our most popular lifters are key way lifters. A step up from there is our roller-guided lifter. All the same technology goes into every level, they’re just all located and held in differently.”
The key way lifter is used by most performance engine builders, especially those who build engines for Sprint Cars, NASCAR and Pro Stock applications. The key way lifter has good durability and it allows the opportunity to put in a larger diameter roller with a larger diameter lifter, which is always appealing to engine builders. They’re also very easy to install.
“Like all our lifters, they’re rebuildable,” McDonald says. “We have some guys who run them way longer than they should. They don’t have any failures, so they don’t put the money into them. Then we have people who rebuild them more often than they have to, like our NASCAR customers who might send them back after every race. In drag race applications, we usually tell them about every 250 passes down the track send them in and let us go through them. It’s a case-by-case basis always driven by application.”
In diesel engines, most engine builders run either solid flat tappet or solid roller lifters. Jesel is a big proponent of the needle bearings for longevity and control.
“In the Powerstroke stuff, the 6.0L, 6.4L and 7.3L all take the same lifter,” Alderson says. “The 6.0L and 6.4L engines are fairly notorious for valvetrain failures – for cam and lifter failure specifically. A lot of people blame the lifters and they’ll find the needle bearings from the lifters in the oil pump, the oil filter or the oil pan. A lot of people are scared to death with the needle bearings and they’re not really the problem. They’re the result of the problem – that being the poor, factory, cam profiles. They tend to tear up the lifters, so anything we can do to improve longevity for the street truck crowd is a bonus. For the competition guys, who are trying to push the envelope, they really needed a better lifter.”
Another thing to keep an eye on, specifically in dual overhead cam options, are lifter buckets. As you start going higher in performance on overhead valve engines with bucket lifters you can collapse buckets and flattened camshafts out.
“The only way to combat that is to put a DLC coating on your lifter and then run a really good camshaft with a really strong surface or DLC the cam as well,” Wilson says.
Out of the many components in an engine, valve springs might not look like much, but they are hands down some of the hardest working parts. Choosing between linear, single coil, dual coil, beehive, or conical springs depends on your application, the rpm range, camshaft characteristics, and anticipated spring pressures.
“Proper valve spring selection involves reviewing the camshaft’s maximum lift, ramp speed and lobe profile,” Risinger says. “High-revving engines require higher valve spring pressures to help keep the valvetrain stable. For many applications, this is accomplished by using a dual spring. It is important that the solid height of the valve spring can accommodate the amount of valve lift applied by the camshaft. The valve spring retainers, and locks may also need to be upgraded to handle the additional loads applied to them when using the higher-pressure springs.”
A lot of people may like running a very linear spring, which is a standard dual coil or single coil. Others may go towards more of a progressive spring, so they get a better rate at max lift for controllability. For Engineered Performance, the shop prefers running a beehive or a conical spring on most applications.
“We’ve kind of gone away from a linear spring application because it becomes quite heavy or cumbersome,” Wilson says. “You’re trying to not only increase your consistency and your valve motion control, but you’re also trying to lighten up the mass as well. There’s a fine line you’re always having to constantly dance around to set up things exactly where they should be. It gets a little daunting.”
For drag applications, Wilson recommends a linear spring over a dual coil spring because it’s got a huge amount of load up top and bottom and it’s going to be super, super aggressive on the bottom at max lift. For a road course application, which needs to be a little bit more refined, he suggests a conical or a beehive spring because you can get away with running smaller retainers and a lighter set up.
“For us in the diesel world, we found that just a better-quality spring than the factory spring usually works pretty well,” Alderson says. “Diesel springs may only be at 30% capacity, even on the higher end stuff. On an LS engine, the springs might be at 60% or 70% capacity. With diesels, at lower rpm, it takes way, way higher pressure to push the same amount of air through a lower rpm engine than a higher rpm engine. If you make 30 lbs. of boost on an LS engine, that’s a lot. Most of the diesels are 30 lbs. from the factory. For diesels to be in the 600, 700 or 800 horsepower range, there’s 60, 70 or 80-lbs. of boost.
“I bring that up relative to valve springs because when you’ve got all that boost and back pressure it’s a dynamic situation. There are pulses in the intake and pulses in the exhaust, and keeping the valves closed is as much a product of boost and back pressure as it is the traditional sense of floating the valve. In a 1,000-plus horsepower diesel engine, you’ve got 3,000 psi of cylinder pressure. When the exhaust valve cracks open, there’s a lot of stress there. From a valvetrain stability standpoint, overcoming cylinder pressure to open the exhaust valve and then maintain control is important.
“The boost and back pressure is a pretty serious variable to overcome that is maybe a little more unique to the diesel stuff than the gas engine stuff relative to spring pressure.”
As most of you know, valvetrain selection can have its complications, but manufacturers of these components do their research too, and are readily available to offer advice so you pick the appropriate parts for your engine application.
Just keep in mind your application, your rpm range and your horsepower goals. The valvetrain puzzle falls into place from there. Part II, coming in a future issue. EB