Most LS2 and LS3 owners chase bigger numbers – higher flow heads and wilder cams – without first considering a crucial dynamic: how intake versus exhaust port flow influences cam choice and how cam split and lobe-separation angle effect power, torque and ultimate driveability. How do you maximise your horsepower per dollar from a camshaft upgrade?

Stock Flow Figures – Knowing the Starting Line

A camshaft upgrade can significantly enhance engine performance.

The original LS1 engine had a more even port flow balance than its newer cousins.  Flowing 242cfm on the intakes and 204cfm on the exhausts, the LS1 (241 casting) has a flow ratio of over 84%.  Port volumes are 200cc on the intake and 70cc on the exhaust.  This required a camshaft with a much closer duration split to maximise its performance.  However, things changed in the LS2 and LS3 engines and that is why revised camshaft specifications are essential.  What previously worked for the LS1 series does not work for maximum performance in the LS2 and LS3.

In stock form the LS2’s cathedral-port heads (same casting as the LS6 243) deliver, at 0.600-inch valve lift, approximately 257 cfm on the intake side and 183 cfm on the exhaust, measured on a 4.00-inch bore.  Port volumes are slightly larger than the LS1 at 210cc intake and 75cc exhaust.  This represents an exhaust to intake flow ratio of approximately 71%.  

The LS3’s rectangular port heads are more generous, flowing approximately 312 cfm on the intake and 216 cfm on the exhaust at 0.600-inch lift.  Even so, the exhaust still lags the intake in percentage terms – a flow ratio of closer to 69%.  Port volume on the LS3 is bigger again with 260cc on the intake and 90cc on the exhaust.

In both head designs, the intake port significantly outflows the exhaust port, which means the exhaust port creates a bottleneck that hinders optimal power and torque production.  If the exhaust gases can not be evacuated completely, then the next fresh incoming intake charge is contaminated by lingering exhaust gas, reducing the amount of fuel and air in the cylinder that can be ignited and diminishing the energy applied to push the piston down the bore and rotate the crankshaft.  It is basic physics but unless you are aware of the problem and know how to rectify it, you will never have an engine that reaches its full power potential.

One way of compensating for this imbalance is to hold the exhaust valve open longer and lift it further open (where possible) to give it more time to evacuate the exhaust gases fully.  Naturally, a set of well-designed exhaust headers is also critical in this formula.

Why Split Cam Duration and Lobe-Separation Angle Matter

A factory LS3 camshaft (204° intake / 211° exhaust @ 0.050-inch, with approximately 0.551/0.522 lift and a 117° lobe separation angle) is fairly mild, chosen to preserve idle and emissions compliance despite strong head flow. 

But dyno testing shows how increasing duration and tightening the lobe separation angle can unlock big gains. Here are some examples of how two of our most popular camshafts perform against a stock LS3.

In dead stock form an LS3 in a VF Commodore with an automatic transmission normally produces 350rwhp. 

The most popular first step to upgrade performance is our Stage 1 package that includes a full exhaust system – headers, high-flow cats and a 3-inch twin back half – with an over-the-radiator (OTR) cold air intake and a dyno tune.  This typically lifts output by over 50rwhp – the dyno shows 400rwhp maximum power.  This is the baseline for subsequent camshaft upgrades because improved intake and exhaust flow are essential for maximising the gains from a new camshaft.

As mentioned, our own split duration camshaft profiles have been designed to make the most of the LS2 and LS3’s unique cylinder head characteristics.

Our No.16 profile camshaft offers the ultimate balance of power and street driveability.  It gives a cammy idle but provides perfect street manners and does not require a high stall torque converter with an automatic transmission.  Fitting the No.16 camshaft to a car already fitted with the Stage 1 package lifts power by another 50rwhp – total power will jump to between 450 and 460rwhp.

Step things up again with our No.6 camshaft and power will soar to between 480 and 500rwhp.  This camshaft delivers the ultimate lumpy idle note and will require a high stall torque converter in automatic transmission cars.

These real world examples clearly demonstrate that the extra exhaust duration gives the LS3’s comparatively weaker exhaust port more time to evacuate its gases, improving cylinder scavenging and letting the fresh intake charge do its job.

Beyond Peak Lift – Maximising the Area Under the Curve

Cam specs are often reduced to a few headline numbers – peak lift, intake duration and lobe separation angle (see our article on Camshaft Terminology for an explanation of these numbers). But in practice, the real key is the valve lift versus duration curve. Imagine plotting lift (vertical axis) against crank degrees of duration (horizontal axis). The curve rises as the valve opens, sustains at high lift and closes. The total area under this curve represents the actual volume of air-fuel mixture that can move through the intake port – or the spent gases that can exit the exhaust port – over the whole cycle.

Maximising the area under this curve produces optimal power in any engine but constraints such as peak port flow at a specific valve lift figure, piston-to-valve clearance and valve shrouding against the bore must also be taken into consideration.  The opening and closing rates must also be considered to reduce the impact of the valve against the valve seat, prevent side loading on the valve stem from excessive rocker angle and to protect valve springs from damaging harmonics.  Valve spring pressure is also a consideration as using stronger springs to control the lifter on the cam lobe also creates frictional losses, robbing horsepower at the crank.

A camshaft with modest peak lift but long duration may in fact move as much or more air than a higher lift cam that opens the valve high but doesn’t keep it there. That’s why world-class engine builders – whether in NASCAR, or NHRA Pro Stock – treat area under the curve as the metric that matters most. They model it mathematically, combine it with flow-bench data and design camshafts that maximise this total flow window instead of purely chasing a bigger lift number.

Most LS cam grinders apply the same philosophy and design lobes to hold the valves open longer in the sweet spot where cylinder head flow is strongest, rather than peaking lift in regions where the port flow is not optimal.

The Roller Camshaft Revolution

This is where modern roller camshafts fundamentally outclass the flat tappet designs of old. A roller lifter can follow far steeper cam lobe profiles, opening the valve more quickly and closing it faster without damaging the valvetrain. The result is a curve with higher ramp rates – meaning the valve spends more time at effective flow lift levels. In practical terms, this massively increases the area under the curve without requiring radical peak lifts that compromise spring life or reliability.

Whereas flat tappet cams of the past had to be relatively gentle to avoid lifter wear and valve float, today’s hydraulic rollers allow aggressive lobes that improve cylinder filling and evacuation, while also delivering much improved valvetrain durability. That is why an LS3 with a modern split-duration roller cam can make 40–60 horsepower more than an old school smallblock with a flat tappet profile, all while retaining manageable idle quality and long service intervals.

Final Figures

Remember that it is not just about lift or duration in isolation – it is about understanding port flow balance and selecting a camshaft that compensates for the weaknesses in the exhaust port.

Active Automotive has developed a range of camshafts for all LS engines that take all these critical factors into account and deliver reliable power and substantial gains for any application.  Whether you have a mild mannered streeter with an automatic transmission or something wilder with a supercharger and high-stall converter, Active Automotive have a proven camshaft for your application – tested on the dyno, the street and the drag strip – after decades of development. 

For a dyno, street and strip proven camshaft upgrade for your LS engine, call Active Automotive on 9456-1111.