The topic of camshafts can be explained both simply and in very, very complex ways. And it certainly makes sense. The camshaft is the brain of the engine and has to work alongside numerous valvetrain components to function properly to achieve a particular engine’s goals for an application. Related Articles - Shop Solutions – February 2025 - Inside the Development of Cylinder Heads - Valve Seat Materials and Machining
We recently sat down with Chris Potter, a valvetrain engineering manager at Edelbrock, and Billy Godbold of Godbold Engineering Solutions, and formerly of COMP Cams, to discuss some of the latest things you all should know about camshaft selection and camshaft design. And there’s plenty to note and be aware of if you want your engine performing well. Camshaft Semi Core
When we talk about domestic cam and block engines, most of us are going to be talking about flat tappet, roller tappet, hydraulic or solid lifters. A lot of times you’re going to make your camshaft decision based on the application and how it came.
“If you had a Coyote that came with an overhead camshaft, you’re not going to switch it over to a pushrod rocker system,” says Billy Godbold. “Likewise, it’d be very expensive to take an LS that was done with a hydraulic roller and try to make that an overhead cam. Where we get confused with there being a lot of choices is like a small block Chevy, a small block Ford, a big block Chevy, a big block Ford, and a lot of the Chrysler engines where you do have both options fairly easy.
“For starters, you have to decide whether you want to have a flat follower riding on the camshaft or a roller follower riding on the camshaft? A lot of times, that’s just going to be decision economics. Then, you have to decide whether you want a roller camshaft or a flat tappet camshaft. Then, you have to decide do I want my adjustment to be manual where you go in there with a feeler gauge and set the lash, or do you want a simpler system that’s less maintenance and go with the hydraulic adjustment? The hydraulic adjustment is really good today. They’re nice pieces, but they have to be looked at every now and then.”
The downside of hydraulic adjustment is with any aeration in the oil. Just like opening a Coke bottle, there’s always micro bubbles inside the engine oil and this aeration in the oil adds some sponginess to any hydraulic adjustment system.
“That sponginess means what you’re gaining in convenience, you’re going to lose a little performance either at high engine speed or low engine speed because the system won’t be as stiff with the hydraulic adjustment as it would be with mechanical,” Godbold notes.
A common theme in today’s camshaft design and selection process is making sure you’re aware of your engine’s overall system when making those decisions.
“You have to see your engine as a system and a lot of times we’ll recommend that people end with the camshaft, not start with it,” Godbold says. “When you’re building an engine, you think about what engine am I going to build? Am I going to build a new Godzilla? Am I going to build an LS? Am I going to build a new Hemi? Then, you start to think about how that engine moves air, so you’ll choose your induction system, your cylinder head, your intake manifold, and then your exhaust system, your headers, your collector, your exhaust. The camshaft is the conductor that makes all of these parts that you’ve put together work well together. That’s the change we’re trying to preach is to go from looking at building up an engine as parts to looking at it as a system.”
In looking at it from a system perspective, experts often look at system stiffness to determine what parts work well together.
“Every camshaft is a variable duration camshaft,” says Chris Potter. “Typically, we want smaller durations at low end to help build torque and larger durations at higher speeds to build power. Well, system stiffness is how much deflection we’re actually inducing into the rocker arm, the spring, the lobe, etc. The camshaft is telling the engine one thing and it’s responding to another. When we start trying to help iron out the specs, we have to look at that system stiffness to see what deflection we’ve got, and then realize that system stiffness is affecting valve events, not durations.”
A valve, to a large degree, is like an unruly teenager, according to Godbold. You tell it to get off the couch and move and it sits there for a little while and until you give enough external force. You have to create this energy to overcome its natural resistance to movement.
“That’s the same thing when you want to open an intake valve because the system isn’t infinitely rigid, it’s going to sit there and deflect until enough load is applied that it actually moves,” Godbold says. “One of the things we try to explain to people is you can’t show your engine your spec card. It doesn’t see the cam that was ground. It sees how the valves move.
“We grind a camshaft taking into account everything in the system to figure out how do we want this valve to move, and realizing that how it moves at low rpm is actually moving the wrong direction from how it moves because it’s going to take the seat timing and squeeze it in and in and in as engine speeds increase based off that deflection, when we really wish it would go out and out and out. With system stiffness, what we’re trying to do is keep it where that change is much smaller from low speed to high speed.”
This newer “system” mantra helps people like Potter and Godbold spec out something better for customers’ goals.
“People understand needing to know simple things like cubic inches and expected rpm, and then you get into how much does the car weigh? What kind of transmission do you run? That all plays very critically into how we spec this thing,” Potter says. “What’s it going to look like on shift recovery? Are you actually racing this all the time or do you want to drive around and have decent street manners and be able to do Saturday night cruises with a car? In that same vein, as our customers understand system stiffness, we get to build better packages. We get to get closer to hitting the durations right every time and helping meet the customers’ goals. That system stiffness is going to be very different on a stock LS engine versus what we’re used to with massive dual springs and even simple aluminum roller tip rockers on a small block Chevy.”
Not only do you have the system stiffness, but you have the system mass as well. For example, on an LS engine, people will go out and spend some money on a really good race rocker system, and then they’ll try to run the same beehive spring and they don’t understand it won’t work anymore because you’ve just put a lot of mass into the system. Despite the rocker arm being better, the system is not.
“A lot of the time, the first questions we’ll ask when we’re doing valvetrain design are about the engine configuration to try to figure out what the engine is going to – what’s the cylinder head like and all these things about the induction system,” Godbold says. “Then, once we know about the engine and the induction system, the next question we’re going to ask about is about the valve spring. What room do you have? What valve spring are you going to run?
“Think of it like Fred Astaire and Ginger Rogers – the valve spring is trying to do everything backwards in high heels that the camshaft is telling it, and then it’s not just what the camshaft tells it, it’s what gets through the system. Then, we’re going to ask things about what’s the diameter of your pushrod? What’s the mass and moment of inertia? When we ask about what rocker arm you’re running, what we’re really thinking in the back of our head is, how much does it weigh? How stiff is it and what rocker ratio is it? We’re looking at stiffness, and we’re looking at mass.
“For mass, we’re looking at the rotational mass, the moment of inertia of the rocker arm. We’re going through the whole system. The camshaft directly controls what the lifter does, so how can we design a camshaft to move the lifter in such a way that through this system it will move the valve in such a way that will not tick off this valve spring throughout the rpm and throughout the number of cycles that it wants. It’s very methodical, and it looks like magic from the outside, but it’s really not from the inside.
After you’ve figured out the valvetrain components that’ll work for your engine and your goals, then you can go in and figure out where you want your four valve events.
“Where do you want to open the exhaust valve?” Godbold asks. “How much overlap do you want in it for your vacuum and where do you want to close the intake? The most important was the intake valve closing, and that’s sort of the simplest one because that really tunes in the rpm, but that’s your main input for where it’s going to make peak torque and where it’s going to make peak power. Exhaust open is going to change how it makes below that or how it makes above that.
“People used to think every 230 duration camshaft at .050 made peak torque and peak power about the same place. It’s because everybody ran about the same lobe separation and about the same intake center lines, so they all had about the same intake valve closing and that’s where people miss how sophisticated picking those points can be because it’s so important to get your intake valve closing right for the rpm.”
According to Potter, in just about every case, he would rather size somebody a touch on the small side than too big when it comes to durations.
“That’s because they aren’t going to notice a lack of 5 horsepower,” Potter admits. “I want to get them all they can, but they aren’t going to notice a lack of 5 hp up top. They will definitely notice that 20-30 ft.-lbs. down low in a street application. Smaller is always going to be a little bit better. You’ll get more smiles on the face that way.”
Whether it’s the street or professional racing, the harder you can get off the line, the less gear you have to run in first gear and the better you’re going to shift recovery coming to second.
“If a car is .040 faster in the first 60 foot, it’s probably .080-.100 faster in the quarter mile,” Godbold notes. “People don’t think about that because you’re always looking at this big number on your dyno chart, but really the lowest rpm that you can reach full throttle, that rpm needs to be circled in red, highlighted, and put 20 stars next to it. That’s the lowest rpm where you’re asking the engine to give you everything it’s got, and where that number is matters so much.
That’s why we ask a whole lot about vehicle weight, gear ratios, torque converters, how many speeds are in your transmission, etc.
“That’s what separates the great engine builders from the not so great ones. Anybody can make a big power number, but you look at the guys who sell a lot of engines in professional motorsports, they almost don’t care about giving you a dyno sheet. Just take this out on the track and see what it does. You’re going to love it and it’ll be exactly the same way on the street.”
To get that level of performance, you have to optimize that overlap triangle with the exhaust opening, intake closing to tune it in for the rpm exactly where you’re going to make those transient changes.
Along with the change in mentality regarding the camshaft and valvetrain as a system, experts are also looking less at durations and lobe separations, and more at valve events.
“We don’t think about lobe separations or durations at all,” Godbold says. “What we thought about is what do we want the engine to do. Then, how do we build the valve events to do that?
“What we’re doing in professional racing is we’re looking at each valve event independently. We’re looking at overlap based on how much room do we have piston-to-valve. We realize if we take out too much, if we put too big of pockets in there, we destroy the combustion.
“On a streetcar, if you put too much overlap in it, you destroy the idle stability. You make it where the car is unruly below a certain rpm. When you put too much overlap in a race application, you carve up the piston top. When you carve up the piston top to get compression, you have to put these popups in it. You have to do something weird in it to mess up the combustion chamber, and then you have the combustion chamber so messed up that it won’t do what it needs to do. It won’t burn quickly enough to extract that energy out of the fuel. That’s where we get into what the overlap is and what we are doing with combustion. We’re trying not to mess up the combustion efficiency of the engine.”
People are hung up on the numbers and it’s understandable why. You give them duration, advance and lobe separation. It allows you to pretty well describe and understand a camshaft, but they’re just byproducts of the valve events and those valve events are what the engine is responding to.
“I don’t think we can ever fully get away from duration and lobe separation, but I do want people to get the idea out of their head that those are what’s affecting their motor and that this duration is what I need because this is what I’m doing,” Potter states. “It’s not the case. It’s where that intake close is going to be, where that exhaust valve opening is going to be. The rest just help set the overlap triangle.”
Engine builders have to go back to what the engine is really responding to. As far as the valve events go, it’s always going to be intake valve closing.
“Find that for a certain intake runner, a certain cubic inch engine, a certain rpm – it’s always going to want that intake closing and you’ll never have to change that again for that engine speed, unless you change the runner length of the runner cross section,” Godbold points out. “Then, you have to decide how much overlap do we really want in there? You’re either deciding you’re overlap based on your low-end vacuum or you’re doing it based on space time continuum. You can’t put a valve and a piston at the same spot at the same time – bad idea.
“The last tuning is usually the exhaust valve opening and you try to move that exhaust valve opening. If you open it later, you’re going to really help it down low because you get a longer power stroke, but you’re going to choke it up high.
“If you look at new camshafts for the LS, Godzilla and Hemi, you’ll see different camshafts that have fairly similar operating ranges, but wildly different durations and lobe separations because they have the same intake valve closing, but different overlap based on the application. If you were driven by durations, you wouldn’t see that, but if you start looking at events, you can see why these two camshafts look wildly different in duration and lobe separation, but are fairly close on intake valve closing and exhaust valve opening.”
Not viewing valvetrain as a system and misusing components is the wrong way of thinking. Whether you’re designing a 20,000 rpm Formula 1 engine, a ship motor or an over-the-road diesel, you’re still trying to design that package to do the absolute best it can do. There’s no shortcuts for this – you have to optimize it around the overall package. EB
Engine Builder magazine is happy to name Sunset Performance Engines its 2024 America’s Best Race Engine Shop.
Prior to starting Sunset Performance Engines, owner Joe Jolly put in his time learning the engine building craft since the young age of 15. Starting out in the Houston area, his early shop experience and love of performance engines led him to the School of Automotive Machinists. Graduating from SAM Tech led to an early career at the NHRA Pro Stock level, gaining years of experience with the likes of John Lingenfelter, Bob Glidden, Larry Morgan and V. Gaines.
While the proper bearing material and bearing selection are important factors, the right alignment of the bearing in the cam tunnel is also critical.
Proper installation may be the most critical factor regarding sleeves, and it’s important to sleeve manufacturers to help engine builders achieve a proper installation.
Detecting cap walk early can be a life saver, so we break down five common causes of cap walk, along with strategies to prevent main caps from wandering off their mark.
Engine builders looking to move the needle on a certain engine platform might decide to design and develop their own billet block.
With 22 years of experience in the performance aftermarket – 19 of which with Kelford – Josh Kemp brings knowledge, expertise and leadership to his new role.
New Performance Automotive has been named Engine Builder magazine’s America’s Best Diesel Engine Shop for 2024.
Engine Rebuilders & Supply is Engine Builder magazine’s America’s Best Vintage Engine Shop for 2024.
Shop Solutions provide machine shop owners and engine builders the opportunity to share their knowledge to benefit the entire industry and their own shops.
Casting Camshaft Content for engine professionals and enthusiasts