Camshaft Specs for LS Engines: What the Numbers Really Mean

Let’s be honest — camshaft specs are one of those things a lot of enthusiasts talk about confidently, but few truly understand. Terms like duration, lift, overlap and lobe separation sound technical enough to impress at a BBQ, but when it comes to how these actually affect performance, many are just nodding along.

So let’s break it down. Specifically, we’ll look at how cam specs relate to LS engines, and why your choice of camshaft should match the cylinder heads you’re using. We’ll also touch on compression ratios, static vs dynamic, and how they tie into cam selection.

If you've been nodding through conversations about cam specs and hoping no one asks follow-up questions — this one’s for you.

Understanding the Basics: Duration, Lift, Lobe Separation and Overlap

A camshaft controls when and how long the intake and exhaust valves open. The “size” of a cam is usually a reference to its specs, not its physical dimensions. A “big” cam doesn’t mean it’s physically larger. It means the numbers on the spec sheet are bigger.

Let’s run through the key terms:

• Duration is how long the valve stays open, measured in crankshaft degrees. More duration generally means more high-RPM power, but less drivability at low RPMs.
• Lift is how far the valve opens. Higher lift allows more air/fuel in (and exhaust out), which can boost performance — but only up to the point that your cylinder heads can handle it.
• Lobe Separation Angle (LSA) is the angle between the intake and exhaust lobes on the camshaft. Tighter angles (e.g. 108°) increase overlap (where both valves are open at the same time), which can improve top-end power and give you that lumpy idle — but it also reduces vacuum and low-end torque.
• Overlap is a by-product of duration and lobe separation. It's the period where both the intake and exhaust valves are open. Great for high-RPM scavenging, not so great for street manners.

Choosing the right combination depends on what you want out of your engine: Street, strip, track, or a bit of everything.

Cathedral vs Rectangle Port Heads: Why It Matters

When it comes to LS engines, there are two main types of cylinder heads: cathedral port and rectangle port. There’s also the LS7 high-port, but it’s a bit of an oddity in the Australian market, having only appeared locally in one car — the HSV W427.

Here’s the kicker: Camshafts are often designed specifically for either cathedral or rectangle port heads. Why? Because they flow differently.

• Cathedral port heads tend to have better intake velocity, especially at lower RPM. They’re great for street builds and are often paired with earlier LS1/LS2 engines.
• Rectangle port heads typically flow more overall, especially up top, but they can suffer from exhaust flow imbalances depending on the design.

Because of these flow characteristics, camshaft profiles for each head type will vary, particularly in the intake/exhaust split (the difference between intake and exhaust duration). Rectangle port heads often need more exhaust duration to compensate for reduced flow on that side.

So if you're swapping cams, make sure it’s matched to your heads, otherwise you could be leaving power on the table.

Static vs Dynamic Compression: What the Cam Doesn’t Tell You

You’ve probably heard someone say, “you need more compression to run that cam.” But what does that really mean?

There are two types of compression ratio to consider:

• Static compression is easy — it's the ratio of the total cylinder volume (at bottom dead centre) to the volume at top dead centre. It’s calculated based on engine geometry.
• Dynamic compression takes into account when the intake valve actually closes — which is affected by cam timing. A cam with long duration and late intake valve closing effectively reduces cylinder pressure, which lowers the real-world compression your engine sees during operation.

So, the bigger the cam, the more static compression you need to bring dynamic compression back into the sweet spot.

For example, if you throw a 240/250 duration cam into an engine with 9.5:1 compression, it’ll feel lazy down low and make most of its power up high: Not ideal for the street. But pair that same cam with 11:1 compression and suddenly it comes alive.

Understanding this relationship helps explain why just throwing in a "big cam" doesn't automatically mean more power. It's got to work with your compression, heads, and the rest of the setup.

What’s the Right Cam for Your LS Build?

At the end of the day, there’s no “perfect” camshaft — it all depends on your goals. A cam that works beautifully in a high-compression, rectangle port track car could be a pain in the neck in your daily driver.

That’s why it’s so important to consider:

• Your head type (cathedral vs rectangle)
• Your compression ratio (static and dynamic)
• Your intended use (street, drag, circuit, towing?)
• Supporting mods (intake, exhaust, converter, gearing, etc.)

When all those pieces line up, the right camshaft can transform your engine. Get it wrong, and you’re stuck with poor throttle response, no bottom-end torque, or a car that barely idles at the lights.

Still not sure what all the numbers mean? That’s what we’re here for. We’ll help you pick the right cam for your LS build. One that actually suits your heads, compression, and driving style.

Because knowing the specs is one thing. Understanding what they do? That’s where real performance begins.