Adding some forced induction to your engine is a serious way to create more power. Both superchargers and turbochargers change airflow dynamics to cram more air into the engine. It takes the timing of the camshaft to maximize potential, and a naturally aspirated cam just isn’t designed to deliver the best results.

In this article, we’ll review camshaft basics and why forced induction camshafts are different, plus what you’ll need to know when choosing one. We turned to Jesse Perkins, R&D Testing Manager at Texas Speed and Performance, to learn more about boosted camshafts.

Camshaft Basics

Before we get into specific camshaft profiles for forced induction, let’s review the fundamentals of how a camshaft works and why boost changes everything. In basic terms, the camshaft times the intake and exhaust valves.

The intake valve opens, and the air/fuel mixture is drawn in by the piston’s downward intake stroke. Compression, then combustion occurs, and next the exhaust valve opens to release spent gas on the upward piston exhaust stroke. In this moment, there is often an overlap in valve timing to allow for exhaust scavenging. Scavenging improves performance by using the pressure difference between the exhaust and intake sides to further help draw in the fresh air/fuel charge for the next cycle.

That process works well in a naturally aspirated engine. What happens if you add a turbocharger or supercharger into the system? The pressure dynamics shift and will try to make optimum power in ways that the naturally aspirated camshaft profile isn’t designed for.

A forced induction cam will open and close the valves at drastically different times compared to a naturally aspirated camshaft.

How Forced Induction Impacts Camshaft Design

First, it’s important to understand that not all forced induction setups are the same, and camshaft spec differences. In each setup, it comes back to camshaft characteristics, taking advantage of boost pressure at just the right moment.

“The differences can be significant because each setup has unique airflow characteristics and needs,” Perkins reveals. “Turbocharged engines rely on spent exhaust gases to spool the turbo, so their camshaft profiles are designed to optimize that energy. In contrast, supercharged engines benefit from quickly evacuating exhaust gases to keep the intake charge fresh and cylinder pressure high.”

To dive even further, not all superchargers are the same, either. A positive-displacement (Roots or twin-screw) supercharger is belt-driven off the crankshaft and moves a fixed amount of air per engine rotation to deliver consistent boost. A centrifugal supercharger is also belt or gear-driven, but it turns a high-speed impeller and creates more boost as RPM increases.

There’s a difference in camshaft design between positive displacement and centrifugal superchargers. “The main difference lies in how and when each supercharger makes power. Positive-displacement blowers provide immediate boost from low RPM, while centrifugal superchargers build boost progressively as RPM rises. Cam design can be tailored to take advantage of these characteristics,” Perkins explains.

Supercharged Cam Specs

As explained earlier, a supercharged application needs to quickly expel exhaust and keep cylinder pressure high. This will require a camshaft that optimizes this variable, and it will be different from what a turbocharged engine requires.

“Blower cams typically feature a wider lobe-separation angle to reduce valve overlap. The goal is to keep as much boost in the cylinder as possible, maximizing power. Put another way, if the overlap is too great, the added boost pressure will blow some air/fuel charge right out the exhaust port,” Perkins notes.

Cam profiles vary between a positive displacement and centrifugal supercharger design, too.

“With a positive displacement blower, boost is available early, so you’ll want a cam that doesn’t bleed off pressure at low RPM. These cams usually feature wider LSAs and conservative overlap,” explains Perkins. 

While the centrifugal supercharger also enjoys a healthy exhaust, its intake design wants to be notably different. “Centrifugal setups benefit from earlier valve events and tighter intake centerlines to improve low-end response and help build torque before peak boost arrives. A well-matched cam will help flatten out the torque curve and make the setup feel more responsive throughout the RPM range,” Perkins says.

The wrong cam in a turbo application will cause a lot of problems in the performance department. A turbo cam needs to be designed not only to make horsepower, but it also needs to help the turbo spool.

Turbocharged Camshaft Specs

Unlike superchargers, a turbocharger needs exhaust gas to build boost. While that means efficently getting the exhaust gasses out of the engine, it also means there will be higher exhaust pressure to contend with. This is going to change how the camshaft needs to be designed so it can help the engine produce good power.

“Turbo cams often run slightly tighter lobe separation angle than blower cams. Though not as tight as in naturally aspirated builds. It encourages spool-up without bleeding off too much exhaust energy. The overlap and timing adjustments help balance turbo responsiveness with peak power,” Perkins states.

To illustrate the difference, let’s compare camshaft specs for a 2015 Chevy Camaro SS running 400-plus cubic-inch LS stroker engine with LS3-based heads for mild drag strip competition.

Note, as lift remains the same in this example, there’s considerably less duration with forced induction and wider lobe separation angle. Specs can vary based on other setups.

Avoiding Common Forced Induction Cam Selection Mistakes

Avoiding mistakes starts with a plan. Define your goals and consider how boosted air/fuel flows through the engine, across the RPM range, by means of camshaft timing. Do you need low-end torque for drag racing or high-RPM horsepower for road racing, or drifting? Where do you need to place your power curve to be most effective? Do it right and match a boosted camshaft profile to your choice of forced induction.

Conventional naturally aspirated engine thinking is that bigger is always better. That’s not the case when choosing the best camshaft profile to match a forced induction setup. It’s all about balance.

“One of the most common mistakes is going to be cam size. Oversized cams can make your setup sluggish or unresponsive, especially down low. With boost, more airflow is already being forced into the engine, so you don’t need excessive duration to fill the cylinders. In fact, too much duration and overlap can bleed off boost, hurt turbo spool, and reduce drivability. Bigger isn’t always better — it’s about balance,” Perkins explains.

Seeking experienced guidance from a reputable engine builder or camshaft manufacturer can also help you get it right the first time for your particular goals and setup. These shops and companies, like Texas Speed, have helped people build all kinds of boosted combinations. They will have insight that will prevent disappointment on the dyno and issues when it comes to how a combination will behave on the street.

“Another common mistake is not considering your boost curve or how your supercharger or turbo behaves. Matching the cam to your power adder and your goals is key,” Perkins states.

Boosted camshafts are not a mystery, they’re crafted to make sure an engine can gain the most power from forced induction. Balancing valve timing and duration with the correct camshaft profile takes advantage of the way boost changes pressure dynamics. Whether you’re installing a turbocharger, positive-displacement supercharger, or a centrifugal supercharger, there’s a camshaft that’s going to help you get the most performance and drivability out of your power curve.