Roller cams have a couple of advantages over traditional flat tappet camshafts: they reduce friction, and they can be ground with more aggressive cam lobe profiles to make more power. You can also swap roller cams without having to replace the lifters. But the roller cam’s main disadvantage compared to flat tappet cams is its higher cost. A roller cam is no more expensive to manufacture than a flat tappet cam (unless it is being CNC machined out of billet steel), but the roller lifters are more complex and costly to make.
The use of roller cams is also against the rules in certain forms of racing. You can’t run a roller cam in many dirt track and circle track classes, stock eliminator drag racing (older cars), some types of marine racing and truck pulling, or vintage road racing. NASCAR rules prohibit the use of roller cams. So there are a lot of applications where a traditional flat tappet cam is the only type of camshaft you can put in an engine.
The development of new camshaft profiles is an ongoing process that will never stagnate. There are a lot of proven grinds that work well in various engines. Many of these grinds have been popular for years.
But with so many stroker engines being built these days, and a proliferation of high-flow aftermarket cylinder heads for a growing number of older engines, cam grinders are always looking for the next innovation that can give their customers a performance edge over what’s currently available from their competitors.
Engines make power with their cams, cylinder heads and carburetion. All three have to work together to create the most usable power within the engine’s rpm capabilities. A huge carburetor and a killer set of heads won’t achieve their maximum power potential if the cam doesn’t have the right grind to optimize airflow. The cam lift, duration, valve overlap, lobe centers and offset also have to match the application – which creates a real challenge for the street performance engine builder who is trying to achieve the often conflicting goals of lots of power and good drivability.
Brian Reese of COMP Cams said his company has been developing new flat tappet cams for a variety of applications, including popular small block and big block Chevy, Ford and Chrysler engines as well as some of the older engines such as Ford flatheads, Ford Y-blocks and Buick Nailhead V8s.
“One of the recent improvements we’ve made is to redesign the cam itself for improved durability. We’re using a larger radius between the cam lobes and shaft. We have also increased the width of the lobes. Older style flat tappet cams have no radius where the lobes meet the cam, which creates a stress point that could lead to cracking and cam failure.”
COMP Cams also has a new line of street performance flat tappet hydraulic cams called “Thumpr” cams. According to Reese, the two things muscle car and street performance enthusiasts want most in a new camshaft is1) more power and 2) a meaner sound.
Everybody likes the rumble that a hot camshaft makes at idle. But traditional race cams that really produce a lot of power at high rpm are usually not very drivable on the street. Long duration cams with lots of overlap typically produce little vacuum at idle, have poor throttle response at low rpm, and may not produce as much torque as a stock cam until the tach hits 3,000 rpm or higher.
One of COMP Cams customers said, “I want you to build a street cam that really thumps.” So the Thumpr family of camshafts was created to satisfy both the need for more usable power and the kind of rough idle that says, “Watch out, I’m bad!”
Street performance cams need to deliver good low-end torque. Traditionally this is done by shortening the duration (the amount of time the cam holds the intake or exhaust valves open) and reducing overlap (the period during which the exhaust valve is closing and the intake valve is opening). Reducing the duration and overlap improves low end torque and throttle response, but it also makes the engine idle smoother and quieter. A wimpy sounding idle is not what most street cam customers want.
To create a hotter idle sound, Reese says the Thumpr cams have extra overlap built into the exhaust lobes to hold the exhaust valves open longer. The result is a longer and stronger exhaust pulse that really sounds great with no sacrifice in drivability or low rpm power.
The Thumpr cams are also ground on a narrow 107-degree lobe separation. For comparison, COMP Cams Xtreme Energy Cams are ground with a 110-plus degree lobe separation angle. The Thumpr cams also have five degrees of built-in advance, which puts the intake centerline at 102 degrees for good low end torque.
Dereck Scott of Lunati said his company’s new “Voodoo” line of street/strip performance cams feature both solid and hydraulic flat lifter and roller lifter designs with revised lobe profiles that maximize the open valve area under the lift curve. “These cams can provide good power, torque and drivability without losing vacuum at idle, and are designed to handle engine speeds up to 6,000 to 6,500 rpm.”
Lunati also has a new “Hydraulic Race Lifter” with tighter internal tolerances that allows it to be used with either hydraulic or flat tapped camshafts. “The new race lifter acts like a solid lifter at higher rpms, but still takes up the valve lash like a conventional hydraulic lifter at lower speeds. It can handle up to 7,500 rpm with no float,” said Scott. The lifters are available for SB/BB Chevy and Ford engines.
Scott Scovrowski at Howards Cams said his company has redone the profiles on a number of OEM muscle car cams to improve their performance. “Our cams have revised ramp rates and lobe designs that produce more power than the original designs.”
Cam Lubrication Issues
The biggest issue with flat tappet cams in recent years has been the reduction of anti-wear additive in current motor oils. The Environmental Protection Agency has required oil companies to reduce the level of zinc and phosphorous (zinc dialkyl dithiophosphate or “ZDDP”) in their motor oils to help prolong the life of catalytic converters. The reduction of ZDDP began with “SM” rated motor oils starting in 2004, and reduced even more in “SN” and GF-5 motor oils introduced in 2010.
Reduced levels of ZDDP cause no problems for roller cams or OHC roller tappets because the friction loads between the rollers and cam lobes are much less than those on a flat tappet cam. But for engines that are still running flat tappet cams (especially with stiffer valve springs), the reduction in ZDDP has increased cam lobe and lifter wear significantly, and caused many cams to fail.
That’s been good for the cam replacement business but not so good for those who drive or race vehicles with flat tappet camshafts.
George Richmond of Melling said the cam failure problem really peaked two to three years ago when the oil companies reduced the level of ZDDP in their motor oils. “Today, we’re seeing maybe 25 percent of the cam failures that were occurring during that time period. More people are aware of the problem and are taking the right steps to correct it.”
The fix for this problem has been to (1) coat the cam lobes with an anti-wear engine assembly lube when the engine is build, (2) and to use a racing oil or diesel oil that contains adequate levels of ZDDP, or to add a ZDDP supplement to the crankcase if using a “SM” or “SN” rated conventional or synthetic motor oil. Without the proper lubrication, you can ruin a new camshaft in a matter of minutes.
The risk of camshaft failures during break-in can also be reduced by starting up a new performance engine with lighter valve springs. Richmond said he advises customers to break in a new cam with no more than 100 lbs. of closed valve seat spring pressure. Run the engine at 2,000 rpm to make sure there is plenty of splash lubrication (don’t let it idle!). Once the cam and lifters are broken in, you can switch to stiffer springs.
Richmond also said that if you want to run more than 100 lbs. of closed valve seat spring pressure (300 PSI open pressure) in an engine, you should replace the flat tappet cam with a roller cam and roller lifters.
“You also need the correct amount of taper on the cam lobes to spin the lifters, and good quality lifters with the right amount of convex on the bottom,” said Richmond.
Several camshaft manufacturers we interviewed for this article (Crane & Howards Cams) told us they are now grinding more taper on their flat tappet cam lobes to improve lifter rotation. Spinning the lifters reduces friction and spreads the wear out across the bottom of the lifter to reduce both cam and lifter wear.
On some older engines, such as vintage 1957 to 1966 Buick Nailheads, the original cams were designed to work with flat bottom (no convex) lifters. On these engines, lifter rotation was achieved by offsetting the lifter bores with respect to the center line of the cam lobes. That’s important to know if you are rebuilding one of these other engines and want to correctly match the cam and lifters. Using modern convex bottom lifters with a vintage cam designed for flat bottom lifters will create a mismatch and likely lead to cam and lifter failure.
Likewise, you should never use flat bottom lifters on a cam with tapered lobes that is designed for convex bottom lifters. Flat bottom lifters will ride on the edge of the taper, creating very high loads that will lead to rapid cam failure.
NOTE: A “flat” bottom lifter may actually have a small amount of convex (maybe as much as .005?). By comparison, a modern solid or hydraulic lifter with a crowned bottom will have .0008 to .0015? of convex across its surface.
Though camshafts are often sold separately, most cam manufacturers say the best way to buy a cam is to buy a kit that includes all new lifters that are properly matched for the camshaft.
A kit reduces the potential for mismatches and premature cam failures. When worn lifters are used with a new cam, or vice versa, there’s a potential for rapid wear and failure.
Improved lifter designs can also reduce the risk of lobe wear and cam failure. Some companies now make lifters that have a small pin hole in the bottom of the lifter to feed oil directly to the lobe. The hole may be centered over the lobe or offset slightly to one side. Another trick that can improve cam lubrication is to cut a small slot in each lifter bore so oil can drip down directly onto the cam lobes.
Another way to reduce cam lobe wear is to have the camshaft nitrided. Nitriding is a process where the camshaft is baked inside a sealed chamber at high temperature while being exposed to a pure nitrogen atmosphere. As the nitrogen diffuses into the surface of the iron, it forms a hard layer a few thousandths of an inch deep that improves wear resistance. It’s not a coating and does not change the dimensions of the camshaft.
Some cam manufacturers offer nitriding as an option. The treatment costs about $100, and increases the surface hardness of the cam to about Rockwell 55 to 60. Some say the bottoms of the lifters should also be nitrided, but others say if the cam lobes and lifters are the same hardness it may increase the risk of galling during break-in.
Some cam suppliers use a process called “Parkerizing” that applies an acidic lubricant to the outer surface of the cam to protect against galling during break-in. It’s a temporary treatment and does not change the hardness of the cam.
Another way to reduce cam wear issues is to use an iron alloy that contains more nickel, or to go with a billet steel cam (both of which are more expensive than cast iron). Chase Knight of Crane Cams said his company is now using an upgraded camshaft material that is about three points harder than a standard cast iron alloy. Crane also offers a micropolished surface finish that reduces friction and improves the break-in process.
For more information on cams and lifters, search our listings on www.enginebuildermag.com.
Latest posts by Larry Carley (see all)
- Front-Mounted Oil Pumps: Good or Troublesome? - Jul 2, 2014
- Replacing Crankshafts, Connecting Rods and Bearings - Jun 27, 2014
- Turbochargers: Small Engine Performance Future - May 22, 2014