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probably due to being a novice, I found this article to be very helpful...thanks, stephen

Camshaft Tech: Flat Tappet vs. Roller
Upgrading to a roller camshaft; is it cost efficient?
Pictures and text by Eric LaBore

Camshafts have always been and continue to be the basis of argument among many engine builders and car enthusiasts alike. How much lift, the right duration, lobe centerlines and separation angles, there are so many aspects and conditions to consider. It requires many years of research, experience and an in depth understanding of the internal combustion engine to become an expert in choosing the best possible design. However, one thing that is widely agreed upon; for the best performance and reliability, a roller camshaft is the way to go.
There are two basic categories among camshafts; flat tappet and roller. Flat tappet cams are the ones most people are familiar with. Most of your V-8 engines in the muscle car era came standard with a flat tappet cam. The tappet, more commonly referred to as the lifter, is, for the most part, flat on the bottom. Oil film is the only thing between the lifter and camshaft lobe preventing them from welding each other together. Eventually, the cam lobes would wear down to a circular shape rather than the teardrop shape they started as. This, in turn, would not open the valves far enough to completely fill the cylinders with a fresh charge of air and fuel or allow the used charge to fully exit through the exhaust. A major loss in power and efficiency was the result. Fortunately, the roller cam almost completely eliminates this wear factor. Roller camshaft lifters are equipped with an actual roller that rides on the cam lobe. (Figure 1) This obviously results in a much longer lobe life due to the reduced friction.
In addition to the reliability factor, roller cams also have a great performance advantage over the flat tappet. The faster you can get the intake valve to maximum lift, the longer it can stay there before the piston comes rushing back up the cylinder to compress the air fuel mixture. If the goal is to load the cylinder with as much air and fuel as possible, the longer you are at maximum lift the better. Flat tappets require a smoother transition from the base circle of the cam to max lift, leaving less time for the lifter to dwell there. Roller lifters, on the other hand, can survive a much more abrupt transition resulting in extra time at max lift. If you compare a roller cam lobe to a flat tappet lobe, you can see the roller cam has a larger radius at its peak, holding the lifter at max lift for a longer duration. (Figure 2)
With all that said, I think you would agree that a roller cam is the better choice from a reliability and performance standpoint. Now let’s look at some of the things required with the use of a roller cam.
To keep lifters on a flat tappet cam wearing evenly, they are designed to rotate in the lifter bore with each revolution of the cam lobe. Not only is this not required on a roller lifter, it is definitely not desirable since rollers only work in one direction. There are two ways to eliminate the rotation of a roller lifter in its bore. On newer blocks that came standard with a roller cam, the top of the lifter bores are machined flat. The upper body of the lifters used with this type of block is also machined flat on two sides. This allows for the use of a special retainer, often referred to as a dog bone, which prevents lifter rotation. (Figure 3) If an older version block or a solid roller cam (often used in higher RPM and racing applications) is being used, tie bar lifters are required. In this design, the intake and exhaust lifters are connected by a flat bar preventing any rotation. (Figure 4)
To prevent cam walk, flat tappet cam lobes are slightly tapered, keeping the camshaft centered under the lifter bores. Since rollers must have a flat surface to roll on, roller cams require another way to keep the cam centered. Some blocks accept a retainer plate that bolts to the block behind the cam gear. Only a roller cam that is machined to accept this retainer can be used. (Figure 5) If the block or camshaft does not accept this retainer, a thrust button must be used. Thrust buttons fit between the front of the camshaft and the timing cover, preventing the cam from walking forward. (Figure 6) Rearward movement, in all cases, is controlled by the cam gear.
One last thing must be upgraded with the use of a roller cam. Since the opening and closing ramps of the cam lobes are usually more aggressive, a higher rate valve spring must be used. If not, the lifter could actually lose contact with the cam lobe at high RPM. The stronger spring will also prevent the valve from bouncing off its seat when it is slammed shut.
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Roller cams do add weight to the valve train. That weight has to be accelerated and decelerated the same as a valve train of lighter weight. That is why they need the heavier springs. The heavier springs increase stress on the valves and the whole valve system increasing the load on the timing gear and increasing the amount of vibration thedistributer gear sees also. So it isn't as simple as what they lay out here. I agree you get more performance, but I believe you trade less durability to get it.
OK I guys I agree with you on this issue, but consider what going on with motor oil and appartently there have & are taking an additive called ZDP out of the oil. Without this additive our older style engines before 1990 need this additive for regular tappet cam system and the oil out now (except racing oil) will wear the bottom of tappets & cam shaft down ( metal pieces in engine) and then theres a potential of needing a complete overhaul. So if you go to roller tappets you dont have to worry- so when rebuilding an engine I would put roller tappets in the motor or spend $4-6 per quart on racing oil-ya know the oil will continue to go up, well thats my 2 cts
STP (blue) will give you all the ZDP that you need. It's a lot cheaper then a roller valvetrain.

Pick any cam company catalog and look at the roller grinds you will find that the timing events are almost exactly the same as a solid lifter cam profile.

I happen to strongly disagree with the roller camshaft is a "gift from Heaven" scenario.

The best engineering logic is to make "it" as simple as possible, not as complicated.

It's you money. Spend it where you like. Like the ad says, "pay me now or pay me later" (we don't care).

Virtually anything that you can do with a roller grind you can do with a flat tappet.

The lack of ZDT in oil is an absolutely ridiculous reason to go to a roller set up. ADD it for $5.

Just my 1-1/2 cents, or is it sense?
Compared to a flat tappet street cam, a roller street cam designed for a similar powerband opens the valves more quickly, lifts the valves further off their seats, holds the valves at maximum lift longer, and then closes the valves more quickly.

Hydraulic roller cams tend to float the valves at a lower rpm compared to the hydraulic flat tappet grinds. Although the weight of the roller lifter is a factor in this, the more agressive ramps are also a contributing factor. Either set up will require a good roller rocker, a heavy wall push rod and the recommended valve springs. Its just a little more necessary with the roller cam.

Also be aware there are two styles of hydraulic roller lifter: the Ford style that uses dog bones and a spyder to orient the lifters; or the Crane style that uses a link bar. The Crane style lifter has a much higher rpm capability.

If a knowlegable motor builder like MME is selling you the parts, you shall have no problems with valve float at an early rpm.

If its in the budget, the roller cam is highly recommended. You'll make more bhp and reduce frictional losses. The worry about zddp in motor oil becomes a moot point.

Look at the photo below, you can see with the naked eye the difference in lobe profile between the two cams, even though both cams have very similar specs. The flat tappet cam lobe is more "pointed", the roller cam lobe is more blunt, because it holds the valve open at maximum lift longer.


Images (1)
  • lobes_001
whoa cowboy

one cannot imply the bulk of the difference in visible profile nets more time-at max lift or area under the curve,

The roller cam's contact point is more centered, so a wider lobe is required to get the same lift for a similar cam position.

Similarly, the flat tappet hits the cam with its leading edge and falls of its trailing edge, so a narrower lobe is required.

Not denying the roller is capable of all you said, but I maintain it is not as dramatic as the photo implies.
As it was explained to me by Omar the Magnificent, back in the old days, either on a mountaintop in Tibet or a massage parlor in Encinido, I can't remember which, is that the advantage a roller cam has over a flat tappet cam is simply that the roller can open and close the valves faster then the flat tappet cam can.

The cam does this by making the ramp steeper. Too steep for a flat tappet lifter to maintain contact.

The value of faster opening and closing of valves is increased torque due to greater port velocity. There was always a lot of incense in the room when he spoke so I was always very lightheaded. That makes it hard now to remember what he said, so cut me some slack here. After all it was the '60s.

The problem with opening and closing rates is that you can over do it very quickly. What happens is that the valves start to slam on their seats. Too much slamming and good.

Of course now these are good new days and the main reason to go to a roller lifter is eliminate the need for ZDT so that your catalitic converter will last 100,000 miles.

There is also this benefit of another .1 mile per gallon of gas. It helps manufacturers fleet averages when they sell a gabillion cars a year.

I think also that one can pick up another couple of degrees of effective duration.

On an all out comp car with big sponser bucks the roller was always the way to go. On a street car that is very unlikely to go 8,500 rpms, except if DT drives it, you aren't really going to see your extra 10hp.

I say keep it simple. Go flat tappet. It's way cheaper and will last a lot longer. I wouldn't drive one of these aftermarket roller setups further then around the block.

The sound of a broken valve train with a roller set up has a terribly expensive schrill and the flat bed might be busy that night.

But it's yo' money to throw away as you see fit. Enjoy. Smiler
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