Flat tappet cams have been around since the birth of the internal combustion engine and are still a viable, cost-effective performance solution to this day.

Exploring Flat Tappet Cams in Modern Engine Building

By Evan Perkins – Photography by the Author

There was a time when the hot-rodding world was flat. Not in the ships-falling-off-the-edge-of-the-planet sense, but in that every hopped-up cam grind was of the flat tappet variety. They were plentiful, cheap, and easy to install. But, much like a vinyl record collection, are they still relevant in the modern performance scene?

In a world of roller cams, roller rockers, and a pace of life that is absolute grease lighting, we stopped to ask if some of the speed parts of our past still have a place in modern engine building. The response from today’s aftermarket manufacturers was a resounding “duh.”

“Hydraulic, flat tappet cams are cheap and still make plenty of power for most street-driven cars,” Zach Woods of Speedway Motors says. “The other place flat tappets are still very common is grassroots dirt track racing.”

“They are still relevant for enthusiasts doing restorations and for those with a low-budget engine build,” Summit Racing’s Carl Pritts points out.

Big-block, small-block, or somewhere in- between, we have used flat tappet cams in many engines with great results. This big-block cruiser packs a flat tappet cam and makes over 600 lb-ft of torque.

But, before we dive any further into flat tappet cams, it seems necessary to point out the difference between them and today’s modern roller grinds. Chevy, in the late ’80s, made the move to roller camshafts. This style of cam relies on a lifter with a wheel built into the end of it that rolls along the camshaft lobes. While it does reduce friction, to some extent, the main benefit of the roller cam is that it can open the valve at a much more aggressive rate than our humble flat tappet grinds. This means that for any given duration the valve will be at higher lifts longer than in a comparable flat tappet grind. Therein lies the benefits of a roller cam—but with complexity comes cost.

Roller lifters are more complicated to manufacture and hence carry a price tag significantly more expensive than a flat tappet setup. “Price is by far the biggest player,” Comp Cam’s Billy Godbold says. The lower the rpm and lift, the less performance you are giving up with a flat tappet camshaft.

One of the concerns with flat tappet cams is improper break-in and subsequent engine damage. With proper break-in, the right oil, and a quality cam core from a reputable manufacturer, you can expect a long healthy life from your flat tappet grind.

For most street engines and boulevard cruisers, a quality flat tappet cam will get the job done and still deliver enough power to put a smile on your face. However, installing a flat tappet cam does come with a unique set of break-in requirements.

Camshaft Survival Guide

There are two major things to understand when breaking in a flat tappet camshaft: good oil and proper break-in procedure.

While it’s easy to think “oil is oil,” when it comes to flat tappet camshafts, they have a very discerning palate–and it comes with a bit of a backstory.

“In the late ’90s, the EPA started to notice that the phosphorous in the oil could attack the catalyst if too much was burnt in the chamber, reducing the life and effectiveness of a vehicle’s catalytic converter,” Godbold says.

“There are, however, still plenty of oils that don’t have as many detergents and have plenty of ZDDP to help protect the cam and lifters,” Woods adds.

While you’ve likely heard of “high-zinc oils” what’s really being refereed to is Zinc dialkyldithiophosphates (ZDDP), which is an anti-wear additive that used to be a standard part of motor oil.

Using an oil that is chock full of the necessary ZDDP to adequately lubricate and protect flat tappet camshafts should be the first box checked on any flat tappet build.

The next concern when installing a flat tappet cam is break-in procedure.

Unlike a roller cam, a flat tappet camshaft relies on a break-in process on first startup. The cam lobe and the lifter need to develop a wear pattern, and their courtship is pretty rushed. Making sure things like carburetor adjustment and ignition timing are very close before the engine is started is key. One easy tip is to use a degree wheel when installing your distributor. This ensures you are within a few degrees of the desired ignition timing.

“The most important note is to immediately run the engine up to somewhere in the 2,500- to 3,000-rpm range at startup and try to vary it inside that range for 30 minutes,” Godbold says. Too many people will turn it off, set the timing, play around with a few settings, and start it up a half dozen or more times before break-in.  Unless there is a fire or the engine is seriously overheating, you really want to get the cam break-in right on the first-time started.”

“Try not to put yourself in a position where the engine would need to be shut down during the break-in process,” Pritts agrees. “The assembly lubricant supplied by the camshaft manufacturer is designed to lubricate during cranking and will be thrown off the camshaft once the engine fires. If the engine cranks excessively or is stopped and started a couple times, the cam no longer has any lubrication and may fail.”

Flat tappet camshafts are largely dependent on oil being flung off the crankshaft to help lubricate the lobes and lifter faces. During cranking, there is little to no oil being slung and a fresh flat tappet cam with no wear pattern can easily be damaged by excessive cranking.

Ultimately, it’s not rocket science, but installing a flat tappet in today’s era can save you some serious coin, and it will work great as long as you step in line with the wise words above.

Sources
AMSOIL
(800) 777-7094
Comp Cams

Speedway Motors
(800) 979-0122
speedwaymotors.com

Summit Racing
(800) 230-3030
summitracing.com

With any high-lift aftermarket camshaft, checking piston-to-valve clearance is extremely important. You should also verify installed valve spring height and make sure the springs are matched to the camshaft. Too much spring pressure will quickly and easily wipe out a flat tappet cam. On applications such as this that require dual springs, it’s best to break the engine in with the inner spring removed, then add it back in once the cam and lifters have established a wear pattern.
Roller cams such as this one use a lifter with a roller wheel built into the end of it. While they are the more advanced, higher- performance solution, they come with a substantially more expensive price tag.
Notice anything missing? The first lobe on this camshaft has gone flat. This is likely the work of low-quality oil with insufficient ZDDP, improper break- in, or too much valve spring pressure.
Flat tappet camshafts, such as these available from Summit Racing and Speedway Motors, are cost-effective performance solutions. If you’re building a conventional small- or big-block Chevy, there are thousands of different grinds available to suit your engine’s needs.
Flat tappet camshafts, such as these available from Summit Racing and Speedway Motors, are cost-effective performance solutions. If you’re building a conventional small- or big-block Chevy, there are thousands of different grinds available to suit your engine’s needs.
Comp Cams offers a few tricks to keep flat tappet lifters alive in demanding conditions, such as street/ strip cars or circle track applications. The lifter (left) uses an EDM cut oil hole that allows a small trickle of pressurized oil onto the cam lobe face increasing lubrication. This lifter bore grooving tool (right) allows extra pressurized oil to reach the cam
Comp Cams offers a few tricks to keep flat tappet lifters alive in demanding conditions, such as street/ strip cars or circle track applications. The lifter (left) uses an EDM cut oil hole that allows a small trickle of pressurized oil onto the cam lobe face increasing lubrication. This lifter bore grooving tool (right) allows extra pressurized oil to reach the cam
This graph from Comp Cams shows the difference in area under the curve between a flat tappet and a roller camshaft. Note that for the same duration, the roller cam is able to achieve more lift for a longer period of time. Godbold says 15 to 20 hp is common between a roller and flat tappet cam with similar specs. Interestingly, he notes from testing on the Spintron there is very little frictional power difference in the flat and roller valve train system.
(Left) A proper break-in oil such as this formula from Driven is a great way to ensure first startup goes as planned. Once the engine is broken in, switching to a high zinc oil, such as this blend from AMSOIL, is a great way to ensure your engine runs healthy for years to come.
(Left) A proper break-in oil such as this formula from Driven is a great way to ensure first startup goes as planned. Once the engine is broken in, switching to a high zinc oil, such as this blend from AMSOIL, is a great way to ensure your engine runs healthy for years to come.
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