How to Pick the Perfect Performance Camshaft for Your Engine

Engine Related Issues

By Rodney (Mechanics)

Without camshaft, any engine may be exposed to stalling, decreased performance, reduced fuel economy, and increased emissions. In pushrod engines, the camshaft is chain or gear driven to the crankshaft while the one of OHC engines can be driven by a belt or gears either to the crankshaft or an intermediate shaft. Due to a 1:It is 2 to 1 camshaft ratio that the camshaft rotates at half the speed of the crankshaft because the latter performs two full cycles of intake stroke, compression stroke, power stroke and exhaust stroke for each power cycle.

Perfect Performance Camshaft

A lot of issues, concerning the camshaft can take place. As the timing chain in engines ages, it will probably be stretched; this creates slack which may cause the cam timing to change, and as a result, compression and torque of the engine are reduced. It also has the potential to influence timing which is ignition related if the distributor is cam-driven. Instead of most OHC engines with automatic chains-tensioning devices, pushrod engines do not. Therefore, replacing the timing chains and gears of high-mileage engines is a necessity for these types of engines.

In pushrod engines, drive system is via chains or gears linked with the crankshaft and in OHC engines, transmitted via belt or chain to the crankshaft or the intermediate shaft. The camshaft turns at half the speed of the crankshaft due to a 1:One-to-two drive ratio because the crankshaft achieves two full revolutions in a single power cycle.

In engines that have belt cams, the main concern is belt itself breaking down as it stops the cam to turn and the engine to stop. If some valves stay open because the belt is broken it could be a case of valves being bent or deformed if there is no place left to move in.

To prevent the damage happen, most vehicle makers suggest replacing timing belts in overhead cam (OHC) engines at specific mileage intervals as part of regular maintenance. For older OHC engines, this interval is typically 60,000 miles, while for newer ones, it’s 100,000 miles.

Cam issues can arise from lubrication problems in the engine. The lifters apply a lot of pressure and friction on the cam lobes, so they need ample oil. Low oil pressure or dirty oil can accelerate lobe wear and lead to lobe failure, causing a cylinder to become inactive.

Using motor oil with the wrong viscosity can also cause this kind of cam damage. In overhead cam engines, it takes a while for enough oil pressure to reach the cam because the oil pump is far from the top of the cylinder head, especially on cold mornings when the oil is thick. That’s why most vehicle manufacturers suggest using 5W-30 oil instead of 10W-30 or 10W-40 for driving in cold weather.

Another issue that can occur in OHC engines is cam breakage or seizure, which might be due to insufficient lubrication but is often caused by head warpage. When an OHC engine overheats, the cylinder head can swell and bulge in the middle, altering the alignment of the cam bores. This misalignment may lead to the cam bending, binding, seizing, or breaking. If an overhead cam doesn’t move freely in the head after removing the belt and cam followers, it may indicate a bent cam or a warped head that requires straightening and/or align boring.

Choosing the Right Aftermarket Performance Camshaft

Replacing camshafts is a common practice to enhance engine power and performance, but selecting the right aftermarket performance camshaft is not easier. Various factors must be taken into account, including the specific engine and vehicle application, compression ratio, fuel delivery system, existing modifications such as intake and exhaust manifolds, cylinder heads, transmission, differential gearing, and even tire size.

But the important aspect to consider is defining your precise requirements for an aftermarket performance replacement camshaft. Do you seek increased power, greater torque for towing purposes, improved fuel efficiency, or other specific performance enhancements?

Selecting the Correct Camshaft

Importance of Selecting the Correct Camshaft Profile

As you browse through the catalogs of various performance camshaft manufacturers, you’ll notice two key points. Firstly, there’s a wide type of camshaft options available, especially for popular engine applications like the small block Chevy. Secondly, each camshaft type comes with specific recommendations from the manufacturer, so better take their advice.

A typical stock replacement camshaft, either reground or new, more or less duplicates the original equipment manufacturer (OEM) specs. These cams are installed to return the engine’s original performance when doing a stock rebuild and are also considered as a safe option.

Going slightly beyond camshaft swaps are cams that have slightly improved profiles like mileage/economy cams, towing cams, and mild performance cams. Camshaft profiles match idling ability, driveability, and emissions levels of stock cams with increased power output and some fuel economy improvement.

Moving towards fully custom cams, however, the choice of the camshaft becomes more complicated due to the fact that every grind is prepared for particular cars. Factors including vehicle weight, transmission type (automatic or manual), drive gear ratios, and engine modifications (compression, displacement, carburetion, valve size, valve train, etc.) become more decisive.

One mistake to avoid while choosing a camshaft is over-caming an engine. This situation arises when a high-performance cam is used to replace a normal cam in an engine, which interferes with the coordination of the components thus reducing rather than increasing performance. Furthermore, the higher duration camshaft with a bumpy idling might not produce the same low end torque as the stock camshaft. Additionally, carbon emission issues may arise just because of long-duration cams.

Camshaft Performance Specs Comparison

By looking at different camshafts you will meet with specifications including lift duration, overlap, lobe separation, and timing.

The valve lift describes the size, an opening that the camshaft provides. Raising the duration of opening the valve is interpreted as the valves will open wider, allowing more air and fuel into the combustion chamber. Improvements in air intake take place until the valve closing area or port size is the limiting factor, or the physical contact occurs between the valve and other engine parts such as the piston, valve springs, retainer springs, and valve guide.

Essentially there are two ways to control the valve lift, by measuring “lobe lift,” which is the maximum height that the cam lobe shifts the lifter. Nonetheless, this determines the real chord’s distance. To figure that out, you should pay attention to the rocker arm ratio, and subtract the valve lash amount. “Gross lift”, frequently appearing in catalogs, is the rocker arm ratio times the lobe lift multiplied. It’s a kind of the theoretical lift of the camshaft. In contrast,” net lift” is an actual valve opening distance after deducting valve lash in the valve train chain.

Duration, defined in terms of crankshaft rotation degrees, refers to how long the cam will keep the valves open. Nevertheless, the duration definition becomes fuzzy due to different measurement and advertising methods types and length.

The measurement of duration is dependent on which and where the measurement is taken. When the cam lobe starts to push the lifter upwards, the valve doesn’t open immediately. Firstly, all the lash in the valve train must be taken up, and the cam lobe gradually rises from the base circle, making it hard to locate the exact moment when the lifter moves.

One way of measurement duration starts from lifter lifts up 0.004 inches above the base circle of cam lobe. The number of degrees of crankshaft rotation will be counted until the lifter descends to within 0.004 inches of the base circle. The most widely used technique is the advertised duration (also known as dumbbell duration). The reason for this name is that those numbers tend to be greater (and sometime misleading) compared to other measurement techniques.

The Society of Automotive Engineers (SAE) specifies that duration should be measured at 0.006 inches above the base circle for hydraulic cams, and 0.006 inches plus the specified valve lash for mechanical solid lifter cams.

However, the most common way of measuring the duration is to establish it at 0.050 inches above the base circle. This ratio is very common in auto parts catalogs, and when it comes to individual recommendations, it is not a rare thing either.

What does a duration marked about a camshaft mean? It implies that the camshaft has certain limitations of generating power within the distinctive speed range of the engine. Usually, a prolonged camshaft duration has a wider range of operating, while a shorter duration one is preferable for low-speed torque and throttle response as it opens the valves for less time.

Camshafts with up to 220 degrees of duration (measured at 0.050 inches cam lift) are deemed suitable for stock unmodified engines and those equipped with computerized engine controls. However, beyond 220 degrees of duration, intake vacuum tends to decrease significantly, affecting idle quality and the performance of computerized engine control systems.

Not all specs provide information on camshaft lobe profiles. Two CAM lobes with the same lift and duration will have different forms. For an example, camshaft can have peak-shaped lobe, whereas another one may have “fatter” lobe. The “V”-shaped structure of the lobe will function differently from the “U”-shaped lobe. Such a difference will affect the duration of the valve opening. Valve float character may also be seen with sudden changes in lobe shapes unless the pressure of the valve spring is increased. Furthermore, profile of lobes on one camshaft is identical for both upward and downward movement, while asymmetrical profile may differ on each side of the lobe.

The most important factor when choosing a camshaft is the timing of the intake and exhaust valves, which is expressed in terms of “valve overlap” (both the valves are open simultaneously) and “lobe separation” (the angle between the centerlines of the intake and exhaust lobes). The longer the lobes, the more overlap of lobes occur, while the shorter the lobes, the less overlap of lobes are observed.

On the other hand, “Stock replacement camshafts with durations under 200°C usually have lobe separations ranges from 112° to 114°.” Most modest performance camshafts come with 110 to 112 degrees of intake and exhaust separations. Typically, cams used for racing has lobe separations of approximately 106 – 108 degrees.

Overlap happens when the intake valve opens before the exhaust valve closes completely. More overlap is desirable in higher rpm performance applications because the outgoing exhaust helps draw more air and fuel into the combustion chamber, improving performance. However, excessive overlap at low rpm reduces low-end torque and throttle response by decreasing intake vacuum. It can also cause idle emission issues by allowing unburned fuel into the exhaust.

Some original equipment cams have more overlap to reduce NOX emissions by creating an exhaust gas recirculation (EGR) effect. However, this compromises low-end torque and throttle response. Replacing such cams with ones having less overlap (more lobe separation) can significantly enhance performance.

Flat Tappet vs. Roller Camshafts

The roller cam is designed to use lifters with bottom tiny rollers in order to decrease the friction effect. In painted engines, roller camshafts decrease friction levels, while in performance versions, these can handle more energetic lobe profiles. The cams providing lift with rollers on top of the cams can hump even steeper slopes as opposed to the flat tappet cams.

Inclining tappets style in camshafts were mainly used until the mid-1980s. Vehicle manufacturers introduced roller-type after that. The lifters on the flat tappet cams have each a slightly concave bottom, thus they always need to rotate while moving along the cam lobes, securing friction and parts’ durability.

The option between these two is propulsive system dependent. For high-performance engines that run on the highest RPMs, the flat tappet cams with solid lifters might be the best option to avoid valve float. On the other hand, solid lifters may be noisy and they need periodical tuning adjustments. Whereas, cam rollers with hydraulic lifters are better for street engines with performance or low RPM engines that produce high torque.

Proper Camshaft Timing Installation

Cam timing indicates how much ahead or behind the camshaft sits compared to the crankham, and it may be checked using a degree wheel and a dial indicator to measure the widening of cam lobes and the duration the intake lobe endures.

An often committed error is to believe that precisely those marks on the cam drive which show the timing of the cam are the right ones. This could be possible for stock cam, yet this is not good enough in the case of the performance engine rebuild. Aspects such as the alignment of the roller cam drive, the wearing of the cam drive and the gear of the cam can cause the cam to either become advanced or retarded. Re-milling of a cylinder head of a OHC mostly works on cam timing, in which cases a thicker head gasket or slight cam drive pulley offset may be required to get the exact synchronization of the cam timing.

Camshaft timing is important as it affects engine performance. Good cam timing is essential for giving the best performance of the engine. The move by 2 to 4 degrees of cam timing could boost torque and throttle response in low-speed operation and RPM running power without any compromise. Furthermore, this cam profile adjusts the valve-lift curve for chain stretch during the motor ageing. Nevertheless, slackening the cam may boost the high RPM but mostly lessen the low-speed output, which is not good for street or stock engine operation.

What’s worth mentioning is that most of these cams don’t have non-zero timing offset when they are installed. These four degrees of advance compensation are employed because the timing chain length tends to increase with engine age.

Camshaft timing is not adjusted with a pointer wheel. If someone installs a shim to achieve four-degree extra advance or replaces the cam drive gear, they might face overshooting and possible piston-to-valve interference problems.

As a matter of fact, it is advisable that flat bottom lifters be replaced together with their cam and lifters pair at the same time. The old lifters can cause a new cam harm, for that reason the new valve springs should also be set in.

When installing a cam, one needs to coat the cam lobes with the parting lube to ensure they keep their shape. In flat tappet cams, apply a high-pressure moly-based CAM paste on all the cam lobes and use motor oil or red assembly lube on the camshaft journals. To lubricate roller cams, apply motor oil or red assembly lube on the lobes and journals, but refrain from applying moly paste lube on a roller cam’s journals.

Flat tappet cams should be broken in following the manufacturer’s recommended procedure, usually involving running at 2,000 RPM for up to 30 minutes during the engine’s initial startup. Roller cams typically don’t require any special break-in; however, it’s still necessary to run the engine at a fast idle for a period to splash lubricate the piston rings as they seat in.

The Impact of Low Zinc Motor Oils on Flat Tappet Cams

If it is a classic muscle car or hot rod that has a flat tappet camshaft then you should be aware of the fact that present day “SM” rated motor oils have lowered the anti-scuff additive called “ZDDP” (Zinc Dialkyl Dithio Phosphate). This deprivation addresses the phosphorus contamination over time by oil-burning vehicle engines, which may increase the tailpipe emissions.

Using lower levels of ZDDP is OK with modern engines that have roller lifters because of the low camshaft lobe loads. However, the older pushrod engines with flat tappet cams may get insufficient protection which results in cam lobes and lifter wear. With tougher valve springs and higher lift rocker arms, the risk is growing.

In order to prevent these problems, you can blend the crankcase oil with a ZDDP additive, use “SL” rated oil, or choose diesel or racing oil with adequate ZDDP levels.

While installing a new camshaft, put moly cam paste which comes from cam supplier on cam lobes and oil or red assembly lube on the bearing journals and do the recommended break-in procedure. Yet, go on adding ZDDP to the crankcase or use oil having enough ZDDP level for further protection.