Do you know how to choose a camshaft? This seems like a simple task because most of us understand what we want from an engine. However, propose this question to 50 Chevy fanatics and you’re bound to receive about as many differing answers because everyone wants something different. Some want that “rumpity-rump-rump” badass idle followed by the roar of power when their foot hits the gas. Others like a civilized idle and good cruising manners. Here’s another question: flat tappet or roller tappet, and why? Some swear by flat tappet camshafts while others who made the switch to roller will never go back.
We’re going to present you with the facts and you can decide what’s best for your application. The humble, spinning reciprocating flat tappet has been a proven performer for nearly as long as there have been internal combustion engines. Yet, in more recent years the roller tappet has been making inroads into production engines and enthusiast builds because of its efficiency and broader range of performance options.
Engines long had mechanical flat tappets that required periodic valve lash adjustment. Cadillac was the first American automaker to put hydraulic lifters in an engine back in 1930, which reduced the amount of maintenance required. One-by-one, other automakers followed suit.
Hydraulic lifters maintain valve lash via oil pressure on the plunger inside the lifter when the engine is running. The plunger maintains pressure against the pushrod, which applies pressure to the rocker arm to keep a minimum clearance at the valve stem. The lifter keeps valve lash snug to where there’s no play between the rocker arm and the valve stem. As the cam, lifter, pushrod, rocker arm, and valve stem tip wear, the lifter keeps up with the wear. Hydraulic lifters fail when they cannot hold pressure at the plunger and thus collapse, causing noisy rocker arm function. And without oil pressure from a healthy oil pump and precision bearing clearances, lifters collapse and valve lash becomes excessive and noisy.
Mechanical tappets are solid and void of a plunger. Valve lash is adjusted mechanically at the valve stem, netting a nice, soft chatter performance buffs love to hear in a high-performance engine. Valve lash clearances are typically around 0.010- to 0.020-inch at the valve stem and rocker tip. Mechanical tappets are also more tolerant of radical cam profiles and high-rpm operation. They maintain constant valve lash at all rpm ranges.
Flat tappets have a time-proven performance history. They’ve won a lot of races and have served untold billions of people very well. The flat tappet advantage is less mass and weight compared to a roller tappet. Although it is easy to assume the flat tappet rides the cam lobe dead center. Nothing could be further from the truth. The flat tappet, be it hydraulic or mechanical, rides slightly to one side of the cam lobe, which causes the lifter to spin on the lobe for more uniform wear. Flat tappet lifters are actually not flat. They have a slight crown on the face of the lifter. The cam lobe is machined with a slight taper, which causes the lifter to ride the taper allowing the lifter to spin as it rides the lobe.
Where flat tappets get into trouble is oil starvation, improper valve lash adjustment, excessive valvespring pressure, and/or improper break-in. A flat tappet cam’s most critical moment is during that first firing. You must have a zinc additive in your engine oil to enable the tappets to work-harden the cam lobes so they will live a long time. Torco Break-In Engine Oil (SAE 30) for engine builders contains zinc and other additives important to proper cam lobe work-hardening during that critical first firing and break-in. Fire the engine and let it run at 2,500 rpm for 30 minutes to work-harden the lobes. Continue to run a zinc additive or a diesel-specific engine oil after the break-in.
And one more thing. When you’re installing a flat tappet camshaft, use the correct assembly lubricant. Cam journals get engine assembly lube. Cam lobes get moly lube, which is that charcoal gray slippery stuff that helps tappets work-harden the cam lobes.
Flat tappet cams are more affordable than their roller counterparts. This factor makes them more appealing going in. However, the benefits of low cost in the flat tappet cam are quickly forgotten when you learn the benefits of a roller tappet cam.
When you position a flat tappet and roller tappet cam side-by-side you can see the differences. The flat-tappet cam (left) is cast iron, which is softer than the hard steel billet roller cam (right) and has lobes that are distinctly different in shape. The roller tappet cam offers a bolder profile that enables greater levels of performance while also reducing friction.
The benefits of roller tappet camshafts are immediately apparent because they reduce internal friction, allow for a more aggressive lobe profile, and they like the high revs. The real beauty of roller tappet camshafts is endurance, which means they have an unlimited lifespan. You can reuse them again and again. The greater benefit of roller tappet camshafts is you can opt for a more aggressive cam profile without the lifters digging into the lobes like with flat tappet cams.
Another nice thing about roller tappet camshafts is how the roller tappets ride the lobes without interruption. They never leave the lobes, maintaining solid contact throughout. And because you have a roller riding the lobe, there’s reduced friction. When you reduce an engine’s internal friction you free up power otherwise lost to friction. Lifters generally come two ways: linked or in a holder, like in LS engines.
Here’s another look at a flat tappet camshaft alongside a roller tappet cam courtesy of Crower Cams. When you observe the lobe profiles the difference is clear. You can shape roller cam lobes any way desired to get the levels of performance wanted. Lobes can be machined to open the valve differently than it closes, and vice-versa.
Reducing Internal Friction
Roller tappets are the point-of-entry for reducing internal friction in an engine, but there’s more. Roller rocker arms reduce friction at the valves. You will find roller rockers are available two ways: bushing or needle bearing. Rocker arms with roller bearings offer the least friction followed by bushings, which are not as efficient. Roller bearings at the rocker arm fulcrum and tip reduce friction even further. However, needle bearings at the fulcrum and tip make a rocker arm more costly. Lifter bore sleeves in the block reduce friction and make the lifter more stable. Torrington bearings at the timing sprocket further reduce friction and free up power.
Whatever approach you take with your camshaft and valvetrain, opt for the greatest amount of efficiency possible while remaining within your budget. If you go roller technology from cam to valve stem expect to spend a lot of money in the short term while saving money and freeing up power over the long haul. The advantages of going roller are obvious. The best way to look at flat tappet versus roller tappet is the long-term investment by going roller. CHP
Here are a couple of flat tappet hydraulic lifters. They’re identifiable as hydraulics by the internal plunger, which is retained by the C-clip inside the top of the lifter.
A flat tappet camshaft is set up where the lobe and lifter ride against each other where the lifter spins on the cam lobe. The lifter must spin on the lobe to prevent destructive and unnecessary wear. Flat tappet cam break-in is critical to long life. The lifter and lobe must be coated with moly lube to work-harden both the lobe and the lifter. Then, you want a steady diet of engine oil with a zinc additive.
Flat tappets are coated with moly lube during installation to give the lobe and lifter a fighting chance at endurance. Never coat the journals with moly lube. Use engine assembly lube on the cam journals.
Note how this flat tappet camshaft is prepared for installation with moly lube on the lobes and engine assembly lube on the journals.
Flat tappets sit deep in the lifter bores. They should be soaked in hot engine oil with a zinc additive and allowed to soak overnight for good penetration.
Here’s a pair of linked Crower roller tappets. Crower manufacturers all of its lifters in its own factory in California. Nothing is offshore due to Crower’s strict attention to quality and race-ready products.
Here are the two types of roller tappets side-by-side. On the left are mechanical lifters (tappets) void of the oil holes you see with hydraulic lifters. On the right are hydraulic roller tappets with oil supply holes to support the plunger and take up valve lash. Mechanical lifters are solid and void of a plunger. Hydraulic lifters will have a C-clip and a floating plunger inside.
The solid mechanical roller tappet is void of a plunger and C-clip.
Hydraulic roller tappets sport the plunger and a C-clip. One area to watch for is the C-clip installation, which must be solid and deep in the groove.
When you examine the dynamics of the flat tappet cam lobe and the roller tappet cam it is easy to see why the roller wins out. A roller tappet can ride the wildest of cam profiles and come back for more. A flat tappet cam is limited.
These are the basic dynamics of a flat tappet camshaft lobe. These are elements that apply to both roller and flat tappet cam lobes. However, the lobe shape is more like we see with a flat tappet cam lobe.
Roller cam lobes can be symmetrical or asymmetrical. The symmetrical lobe offers the same rate of valve opening and closing on both sides of the lobe. An asymmetrical lobe offers a different attitude from one side of the lobe to the other.
Here’s a small base circle roller camshaft from Crower’s inventory. You should opt for a small base circle camshaft when you’re running a stroker crankshaft. The small base circle may be necessary for the rod bolts to clear the camshaft.
The Gen IV and V Chevrolet small-block engines were engineered to run only with a roller tappet camshaft. Here’s one example of what you might see for the Gen IV and V engines. Check out the very aggressive cam lobe on this stick. Note the Torrington bearing at the cam sprocket for reduced friction.
Most camshafts are identified at one end, which makes it easier to trace the grind. This is a Sig Erson camshaft, which makes it possible to look these numbers up.
Jesel produces race-ready valvetrain components, which are available from Summit Racing Equipment. This package, which was captured in John Gulius’ race shop in Wilkes-Barre, Pennsylvania, enables you to install shaft-mounted roller rocker arms on a small-block Chevy. The Jesel products offer both stability and low-friction.
Earlier, we mentioned lifter bore sleeves, which offer stability and reduced friction. Note how these sleeves in a small-block Chevy at John Gulius Race Engines are honed for good oil control.
During a recent visit to Crower, the folks laid out the manufacturing process for us showing their roller tappets, which are produced in-house. From left to right, Crower begins the lifter birth process with a solid piece of billet and begins machining from there. At the far right you have a completed roller tappet ready for installation.
Friction reduction is further enhanced with a roller tip rocker arm. This is a stamped steel low-buck rocker arm nearly anyone can afford. What it means for you is less wear and tear at the valve stem along with reduced internal friction.
Check out these shaft-mounted Jesel rocker arms from Summit Racing Equipment. These are the ultimate friction reducers coupled with an aggressive rocker arm ratio for added lift.
Crower makes these race-ready roller rockers, which multiply lift and offer smooth function at the fulcrum. These shaft-mounted rockers sport needle bearings at the fulcrum and at the tip.
Dave Akard at Burbank Speed & Machine likes these cam sprocket Torrington bearings, which further reduce internal friction at the cam sprocket. These are common to Gen IV and V small-block engines. However, they are also available for classic small- and big-block engines.
Not enough thought is given to valvespring pressure, which is determined by cam profile. You must have spring pressures compatible with the cam profile. Too much spring pressure for lobe lift and you can wipe a flat tappet camshaft in short order. Purchase your cam as a kit with compatible valvesprings.
Dave Akard stresses the importance of proper valvetrain geometry. Pushrod length directly affects valvetrain geometry. Invest in a pushrod checker and set up your rocker arm geometry at the valve stem.
On top, we get a closer look at rocker arm geometry and how it affects the valve stem. You want the rocker tip centered on the valve stem from the time the valve begins to open until it closes. Side loads on the valve stem will eat up the stems and guides.
Torco TBO Premium Break-in Oil is what you should use to break in a new engine because the first firing of a fresh engine is critical to longevity. Protective anti-wear chemistry allows mating surfaces to gently wear in during break-in. Torco TBO contains a high percentage of Zinc anti-wear chemistry for proper valvetrain and new cam break-in protection.
Torco SR-1 Catalytic Converter Safe and SR-1R are special blends of highly advanced synthetic base oils and proprietary additive systems aimed at increasing power, efficiency, and engine protection. Synthetic engine oil is what you want for longevity and less wear and tear. For late-model engines with tight tolerances, opt for 0W20 or 5W30. Older engines will want 10W40 or 20W50.
Photography by Jim Smart; Crower Cams