Muscle Mustangs & Fast FordsHow To Engine
Are There Really Differences Between Blower and Turbo Camshafts?
The Boost Cam Jam
Internal combustion engines are a puzzle of mechanical wizardry designed to convert air and fuel into useable energy. They function by ingesting an air/fuel mixture into the cylinders—the mixture is then compressed, ignited, and burned. The expansion of heated gases (from the burnt fuel and air) creates immense pressure that forces the pistons down the bore, which in turn drives the connecting rods and the crankshaft. Burning more air/fuel mix equals more power, hence the need for forced induction.
Since stock is never enough, we are always looking to increase horsepower and torque. This requires creating a greater force on the pistons to drive the crank harder. Increasing output requires an increase in displacement, improving the induction system (and/or exhaust), or artificially providing more air to the engine with boost or nitrous oxide. Getting more air is often the hard part, as it’s much easier to control fueling.
In the old days engine efficiency was improved by swapping better-flowing heads, installing larger cams, better-flowing intakes, and often a bigger carburetor. Today engines are more complicated, but they still respond to classic hot rodding tricks. Where we once had carburetors and mechanical distributors, we now have electronic fuel injection, drive-by-wire throttle-bodies, and computers that precisely control ignition timing and fuel mapping, amongst other things.
With EFI and modern powerplants, performance enthusiasts benefit from rock-solid drivability—not to mention improved durability, increased power output per liter, and better economy. Gone are the days of pumping the throttle to get an engine to start—and then holding your foot on the throttle to keep it running.
When it comes to late-model Ford engines, forced induction is the single most popular way to pick up substantial power. Supercharging and turbocharging trumps nitrous and H/C/I combos that once ruled the roost. A few intakes are available for the Two-Valve, Three-Valve, and Four-Valve engines, but doing a (ported heads), cams, and intake is expensive and you’ll realize 50-125 hp on most street engines. Considering the labor, you can easily install a blower or turbo and pick up 125-200 hp with ease.
The aftermarket offers dozens of blower kits and a handful of turbo kits for all EFI Mustangs, many of which kits offer OE quality and fitment. And while most make great out-of-the-box power, enthusiasts crave more. Complementing your boost maker with a performance exhaust, free-flowing intake, and an aftermarket camshaft (or camshafts in the modular or Coyote engines) can net you another 50-100 hp or more. In fact, it’s not uncommon to see 600-1,000 streetable horsepower with basic parts.
Simply stated, blowers and turbos force-feed compressed air to the manifold. When the intake valve opens, the fuel air mix is “forced” into the cylinders. But even with boost, stock cams can only take you so far.
We like to say the camshaft is the brain of the engine because cams control the intake and exhaust valves, which lets the air in and out of the cylinders. With that, the cam has a huge effect on cylinder filling. In lay terms, opening the valves more than stock or holding them open longer than stock should increase power, but it’s not as easy as throwing in a monster camshaft. To reach peak efficiency, the cam must be matched to the cylinder heads, turbo/blower, induction system, exhaust system, gearing, and vehicle weight. It’s also important to determine where you want your engine to make peak power. A heavy street car or truck will be most fun with low-rpm power, whereas a light Mustang with a stick may run best with a higher powerband.
Altering the design of the cam can help define where you’ll get your power. Common terms are valve lift (how far the valves are lifted off the seat of the heads) and duration (how long the valves stay off the seat). Lift is measured in inches or millimeters, duration in degrees of crankshaft rotation. But there’s a lot more to it.
LSA (lobe separation angle) dictates the amount of overlap, although this is adjustable on 3V and some 4V engines with Ford’s Ti-VCT system. With most cams there is a short time when the exhaust valve and the intake valve are open simultaneously—this is called overlap. The right amount of overlap can help the engine breathe better. Overlap can improve scavenging of the exhaust and enhance the draw on the intake side to pull in additional mixture. It’s in the area of overlap that you’ll find the biggest differences between blowers and turbo cams—well, sort of.
Because turbo engine rely on exhaust gas velocity to drive the turbo, many turbo cams will be shorter on exhaust duration. This tends to enhance the flow of exhaust gases, which are used to drive the exhaust impeller. Getting the exhaust duration right for your combination results in quicker spool-up and better overall efficiency.
While turbochargers create an exhaust restriction, they also use the energy that would otherwise be wasted. With that, you’ll find that many factory turbos are purposely small. The manufacturers do this to eliminate or reduce turbo lag. This also provides excellent tip-in response, which is great for driving around town or for making a small-displacement engine seem bigger.
And while stock or mild cams can be used universally with bolt-on power-adders, there’s always greater power to be had with a specialized cam, designed to optimize your combination.
For efficient cylinder filling, boost pressure on the inlet side must be greater than the exhaust backpressure. Exhaust pressure rises when exhaust gases encounter the turbine wheel (impeller) and as rpm climbs at WOT. This pressure differential is dynamic and changes as the engine sweeps through the rpm band. A supercharged engine simply wants maximum scavenging to clear the path for incoming charge, which means longer duration on the cam.
Years ago, older turbo designs created more back pressure and thusly builders selected cams that closed the exhaust valve sooner, as this limited back pressure. This was achieved with a wide LSA. With modern housing and impeller designs, backpressure is reduced without a drop in performance, so lobe separation can be snugged up. And as you move to a serious street or race turbo setup, you can get away with more cam, because the intake pressure will generally be higher.
Remember, the air/fuel mixture enters and exits the engine’s cylinders due to a pressure differential between the intake manifold and cylinders. The piston pulling down on the intake stroke causes a drop in pressure in the cylinder, and since pressure is higher in the intake manifold, air and fuel rushes in once the intake valve opens. Therefore, if you can create a bigger pressure differential, the result should be more efficient cylinder filling. Adding boost does just that—it creates higher pressure in the intake and generally more efficient filling when the intake valve opens. The difference in blower and turbo cams is mainly on the exhaust side.
In addition to affecting power, drivability, and emissions, the camshaft has an effect on the valvetrain. And your valvetrain is an important thing to consider when selecting a cam. Stock cams are designed with many factors in mind, such as drivability, desired horsepower and torque, reliability, emissions, and economy. Because engineers have to work within this window, some performance is often left on the table. Of course, stock cams are also designed to work with the stock intake, compression ratio, and exhaust system.
To maximize airflow with an aftermarket cam, you must recognize that your engine may require improved induction, better flowing heads, stiffer valve springs, larger exhaust headers, and more robust pushrods. With all this, you may wonder, “Is the tradeoff of a wild cam worth the extra power?”
We say yes if you are Class racing and need to maximize your combination within a given set of rules. In street engines/strip, a milder cam is often a better choice. Mild cams generally give you better drivability, require less maintenance, and have better valvetrain durability. Plus, in many cases the bolt-on turbo or blower you purchased can provide enough power to surpass the durability of the stock bottom end.
Nevertheless, altering valve timing has long been a way to increase performance, and that trend continues today. Companies such as Comp Cams, Crane Cams, and Lunati have tackled the difficulties in designing and manufacturing camshafts (and valvetrain systems) for the vast array of engines and engine combinations.
Changing any part of the engine configuration will often dictate that a new cam be installed to maximize cylinder filling. And while many cams will work well with a variety of combinations if you’re looking to maximize output it’s important to select a cam with your engine specs in mind.
Another thing to consider is intake runner design because this determines “where” in the rpm band the engine will be most efficient (and least efficient). In other words, as you change different aspects of the engine, the camshaft must also change to maintain maximum efficiency. Longer runners are generally more efficient at filling cylinders at low rpm; shorter runners work best at high rpm.
So, if you’re going to leave your stock intake, you may want to leave the cam stock too. If you have improved induction, you’ll need a bigger cam to keep up. For instance, a 5.4L Two-Valve Lightning engine with a big PD (positive displacement) blower will be very efficient in low- to midrange operation, but those 5.4s don’t need to rev much past 6,000 rpm. With that, you can get away with a smaller cam and stock-type valve springs. In contrast, a drag race Cobra Jet 5.0L may see 8,500 rpm, a feat not often done with stock cams and valve springs.
Our recommendation is that if you are looking for a modest increase in power, most forced induction kits will do the trick in out-of-the-box form and with a stock or mild cam. However, at some point your engine will want more air, and aftermarket cams will be needed.
Yes, a cam swap is in order, but picking the best cam is tricky. Like any mechanical component, there are limitations, and these lie in your valvetrain’s ability to control the valves at high rpm and to maintain proper clearance between the valves and the pistons. A meeting of the latter is often catastrophic.
The good news is that all cam manufacturers have technical departments that can help you with cam selection. And despite what you may have heard, many mild blower and turbo engines seem to like roughly 112-114 degrees of LSA, but turbo cams generally require less duration.
In the Mustang world there are dozens of bolt-on supercharger kits, so the cam companies have an easier time designing dedicated blower cams. There are far fewer turbo kits and, as you can imagine, far fewer dedicated turbo cams. Piston-to-valve clearance will often limit your cam selection, but that’s OK because most enthusiasts will be looking for medium power upgrades.
If you’re going all out, or if you want more education, consult any of the cam manufacturers. They’ll get you dialed in.
Important Factors to Consider
- Inducer diameter
- Exducer diameter
- Turbo size
- Boost level
- Intercooled or not
- Blower type
- Intake manifold design (long, medium, short)
- Compressor and turbine housing A/R
- Horsepower level
- Vehicle weight
- Transmission type
- Street or race