Rob Reaser
September 1, 2001

It seems that just about every stock component of the 5.0 engine can be replaced with an upgraded aftermarket piece designed to boost power output. New 5.0 owners and novice mechanics often focus on these simple bolt-on parts, such as higher-flowing exhausts, free-flow filters, bigger throttle bodies, and the like, for good reason: Their benefits are easy to understand and installation is simple. Camshafts are another area where Mustang owners can prompt a significant increase in engine torque and horsepower. The problem for many beginners is that the camshaft option can be downright scary. Aside from the installation demands (which aren't complicated with a set of good instructions), there's the question of which cam to buy and deciphering those cryptic numbers and terms on cam spec charts, so we'll attempt to clear things up for you.

Our focus is on cam upgrades for '89-'95 5.0L Mustangs. As you're probably aware, these models featured the hydraulic roller cam and roller lifters in conjunction with the mass airflow metering system. The '85-'88 5.0Ls also featured roller cams and lifters, but used a speed-density control system to measure air intake. As a result, cam profiles manufactured for mass air applications aren't necessarily compatible with the '85-'88 roller engines that use speed density.

First, let's look at the basics. A camshaft sits high in the engine block between the cylinder banks and is rotated via the timing chain that's also connected to the crankshaft (which turns the cam). Cams on the '89-'95 V-8 Mustangs are made from steel, instead of iron, which is what the earlier, flat-tappet Mustangs cams were made from. The cam spins on bearings seated in the blocks and features eccentric lobes along the shaft-one for each intake and exhaust valve tappet or lifter. As the cam rotates in unison with the crankshaft, the lobes lift the hydraulic roller tappets seated in the cylinder heads. As the tappet rolls up on the cam lobe, it pushes the pushrod upward against the bottom of the short end of the rocker arm. The rocker arm pivots on a stud and effectively multiplies this lift by a ratio of 1.6:1 on the other side of the arm in stock engines. In other words, one unit of lift on one side of the arm translates to 1.6 times the unit on the other side. The long side of the rocker arm pushes down on the intake and exhaust valves, pushing them into the combustion chamber so that a fresh air/fuel mixture can be drawn into the cylinder on the intake stroke and burned exhaust gases can be expelled on the exhaust stroke. It seems like pretty simple stuff, but as you may expect, things can get complicated.

The camshaft determines the amount of air/fuel and exhaust that goes in and out of the combustion chamber, how it goes in and out, and when it occurs. Changes to these variables (flow, quantity, and timing) can significantly change the torque and horsepower output and rpm powerband (where the most power is created) of an engine. Thus, engine power-and when that power occurs-can be changed, depending on the type of cam you install in the engine. Therefore, power from a cam is delivered in terms of lift (how much the valves open up), duration (how long the valves are open), and air/fuel and exhaust gas speed (how quickly the valves open and where, as determined by the cam lobe profile).

On stock engines, the OE cam is designed for an optimal combination of usable power and fuel economy given the available equipment options: transmission type, rear gear ratios, tire size, and computer system (you'll find, for example, that stock automatic transmission applications can't handle radical cam profiles as effectively as manual transmissions. Most aftermarket cams listed for use with automatic trannies are in the mild-street class). You might want to customize your engine's output and usable powerband to meet specific goals. For example, you can select an aftermarket cam to deliver an overall boost in horsepower without significantly altering the powerband. You may want to get a cam to complement a change to a higher rear gear ratio or different tires. You also may want a cam to deliver more low-end torque for improved stoplight launches or for better horsepower at higher speeds. The possibilities and combinations seem limitless (even though they're not) and would take more space than we have here to thoroughly cover the subject. That's why we recommend you talk to your manufacturer before you make a purchase.

All of the cam manufacturers covered in this story have someone in its technical department you can call who can help you select a cam that fits your needs and equipment. Not only can they tell you the best cam to purchase given your intended driving needs, previous modifications, and drivetrain and tire sizes, they can also point out problem areas that may arise with a specific cam choice (such as the need for higher-rate valvesprings, guideplates, spring retainer and oil seal interference, shorter pushrods, retainer-to-valve clearance, rocker studs, and whether you should pay close attention to piston-to-valve clearances or not). We attempted to select cams that can be installed without further engine (intake/ exhaust) or driveline (transmission/rear gear) modifications.

Also, note some of the cams (OK, the majority) listed here aren't emissions legal for street applications (we attempted to note the ones which are). Keep this in mind when you're looking for your upgrade.

Camshaft Specification Glossary
Peak torque rpm: The rpm at which a specified cam delivers peak engine torque. Theoretically, cams operate at maximum efficiency only at a specific engine rpm. Performance falls off at anything above or below that rpm.

Peak horsepower rpm: The rpm at which a specified cam delivers peak engine horsepower.

Basic rpm range: The engine rpm range at which a specified cam delivers optimum performance. Generally speaking, the more radical the cam in terms of lift, duration, and overlap, the higher the basic rpm range.

Advertised duration: The degree of crankshaft rotation the intake and exhaust valves are actually open. Because of the gradual ramping up and down of the valve lift, it's difficult to precisely determine the beginning and end of lift, even though this is what advertised duration attempts to do. Because of this-and a need to provide a standard industry-wide-manufacturers also list cam "duration," or "duration at 0.050 inch."

Duration (or duration at 0.050): For standardization purposes, most manufacturers rate cam duration at 0.050 inch of tappet lift. Thus, duration refers to the amount of crankshaft degree rotation in which the valves are open (from 0.050 inch on the opening event to 0.050 inch at the closing event). Reading the duration numbers can tell you a lot about a cam's performance. In general, the lower the comparative duration, the more likely peak power will be lower in the rpm range. As duration increases, power shifts to the upper rpm range. Naturally, the trade-off is that as you gain upper-end power, you lose low-end power.

Valve lift: The measure of the lift of the valve. Specifically, it's the lift at the cam multiplied by the rocker arm ratio. For example, a lift at cam height of 0.320 inch using 1.6:1 rocker arms would have a valve lift of 0.512 inch (0.320 x 1.6 = 0.512). Use this same cam with the popular 1.7:1 rockers many 5.0 Mustang owners install and the lift increases to 0.544 inch. As you can see, a combination of a hotter cam and higher ratio lifters can significantly increase valve lift over stock. You must be extremely careful, though, because this combination further reduces critical piston-to-valve clearances.

Lift at cam: The amount of lift of the tappet.

Intake timing (open): The crankshaft degree at which the intake valve opens.

Intake timing (close): The crankshaft degree at which the intake valve closes.

Exhaust timing (opening): The crankshaft degree at which the exhaust valve opens.

Exhaust timing (close): The crankshaft degree at which the exhaust valve closes.

Overlap: The point between the exhaust and the intake stroke where both intake and exhaust valves are slightly open (occurs around top dead center). A siphoning effect takes place here, where the outflow of exhaust gases assists the inflow of fresh air/fuel mixture. This is a critical timing event that dictates how rich or lean an engine will run and directly affects fuel economy, throttle response, emissions, and vacuum.

Lobe separation: Refers to the degrees of rotation separating the peak of the intake valve lift (at the cam lobe) from the peak exhaust valve lift. The closer the lobe separation, the sooner peak torque will build in the basic rpm range. The wider the separation, the more the power will get spread through the basic rpm range, with better power on the upper end of this range.

Intake centerline: The point where the intake valve is opened to its maximum (after top dead center). It's also the reference point at which the cam is installed in relation to the crankshaft (also called degreeing). All cams come with a recommended intake centerline installation point. Advancing or retarding this centerline changes when the valves open and close in relation to the crankshaft rotation or, more specifically, the timing of the piston stroke. Advancing the centerline-say, from a recommended 108 to 104 degrees centerline-keeps the intake valves open longer before the piston goes down on its compression stroke. By adjusting the centerline installation point, you can affect changes to a small degree to maximize power at a specific area on the powerband (low end or upper end). In essence, advancing the cam will shift the basic rpm down the band. Retarding the cam will put the power up at a higher rpm range. Because Mustangs experience traction when low-end torque and horsepower are high, you must make sure you don't give the engine too much advance timing. Advancing the timing too much can also affect piston-to-valve clearance beyond the clearance issues associated with higher valve lift and the use of higher-than-stock ratio rocker arms.

Single pattern: The duration of the intake and exhaust lobes is the same.

Dual pattern: The duration of the intake and exhaust lobes is different.

Compression ratio: Many cam spec charts also give a recommended compression ratio range in which a cam will work. The stock compression ratio (using stock heads, pistons, and rod length) as well as cam duration and centerline position (advance or retard), will affect cylinder pressure. Cams are designed to work with a specific compression ratio, so make sure the cam you buy will work with your setup. Too little compression will reduce engine output while too much compression will cause internal damage, preignition, and detonation.