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What is an Aggressive Cam?

“The ideal cam profile would raise the valves to full lift instantly, hold them open for a specified duration and then close them instantly. The laws of physics make it impossible to achieve instantaneous valve opening and closing, but recent advancements in design technology have made it possible to open and close the valves with more area under the lift curve. By doing so, engine efficiency is improved because the valves spend less time at very low lift” –Harvey Crane

Most people look at a large or a fat cam lobe and automatically assume it is aggressive. They might also say that it has an 'aggressive ramp'. The reality is that you cannot visually see if a cam is 'aggressive' or not. Aggressive is a vague term that is thrown around by people that have little knowledge about camshafts. 'Ramp' is also a term that few people understand. People look at one side of cam lobe and assume its the ramp...well, it is not. When you combine the two words, you get 'aggressive ramp', the ultimate cam buzzword used by people that don't know sh*t about cams; if you haven't noticed, the use of the term 'aggressive ramps' is one of my pet peeves.

So what is a ramp?...Using a Honda K cam as an example, if we use a classic definition of what a clearance ramp is, the ramp is going to be the section of the cam that goes from the base circle (0.000" cam lift) to right around 0.010" cam lift. I don't think it would ever be appropriate to use the term 'aggressive' to describe a clearance ramp; a section of the cam that for the most part is not even in contact with the follower or acting on the valve. Now 'aggressive ramp' makes a little more sense if we use Harvey's definition of a 'ramp'; a definition that I prefer to use. In this case, the ramp is the section of the cam that goes from the base circle up to it's maximum positive acceleration peak; on a K engine this would be the section from the base circle to approximately 0.035" cam lift. Either way, if you insist on continuing to use the term 'aggressive ramp', the reality is that you cannot visually see it!

If you still insist on using the term 'aggressive', you still need to quantify it. To measure how ‘aggressive’ a cam was, Harvey pioneered the idea of cam intensity. He used three different intensity measurements depending on the situation. They were: Major intensity (duration @ 0.020” lift – duration @ 0.050” lift), Minor Intensity (duration @ 0.010” lift – duration @ 0.050” lift), and Hydraulic Intensity (duration @ 0.004” lift – duration @ 0.050” lift). In other words ‘intensity’ described how quickly the cam opened and closed from lower lift points to his standard lift point of 0.050”; the smaller the intensity, the more aggressive the opening and closing.

If we have two cams with identical duration @0.050” and identical lift specifications, but one cam has a major intensity of 24 degrees and the other 34 degrees, the cam with the smaller intensity will perform better. On average the cam with the smaller intensity will open approx. 5 degrees faster and close approx. 5 degrees faster; as a result the area under the lift curve will be greater on the cam with smaller intensity numbers. In practical terms if two cams have the same lift and duration, they should have similar maximum horsepower and torque readings, but the cams with smaller intensity will perform better, idle better, have better throttle response, better lower end power, and a broader power curve.

I also like to look to at what I call ‘100 intensity’ and ‘200 intensity’ numbers depending on the size of the profile. These would be the duration difference between 0.020” and 0.100” or 0.200” respectively and tell me how quickly the cam is opening and closing between those two points.

Impostor4 v S2 Stage3 v S2 Ultra4 v S2 Ultra BMF1

Above you can see a chart comparing the 'intensity'/aggressiveness of some Impostor4 cams versus Skunk2 cams. The irony of this chart is that Impostor4 is considered a good drag racing cam used in the Drag race market, but if you compare, it is less 'aggressive' than even the Skunk2 stage3 cam. The only reason it makes more power than the Stage 3 cam is because it has much more lift and duration. The stage 3 opens and closes 6.74 degrees faster to 0.050", 9.21 degrees faster to 0.0100", and 8.92 degrees faster to 0.200". If we compare Impostor4 to S2 Ultra4, a cam with the SAME lift and duration, you see that the Ultra4 opens and closes 5.89 degrees faster to 0.050", 9.21 degrees faster to 0.0100", and 15.48 degrees faster to 0.200". In other words, the Ultra4 has much more area under the lift curve and efficiency is improved because the engine can breathe much better. Below is a dyno chart of the Impostor4's v S2 Ultra4....both cams have the same lift and duration, but the Ultra4's have lower intensities (faster opening and closings).

S2 Ultra4 is a superior cam because it is smoother and has better intensity

So how aggressive is too aggressive? Believe it or not, S2 Ultra4 has 'ramps' that are only moderately aggressive' because we wanted to design an all-around cam that would be good for the street, strip, and road course. If you look at the intensities of the S2 Ultra BMF drag race cams, you will see that this cam is even more aggressive, but it is still far from pushing the limits. Honestly, we have yet to reach the limits of positive acceleration; a limit that is established by acceleration levels where valvetrain parts actually break or wear down.

PART1...... https://skunk2.com/products/dave-talks-cams-part-1/
PART2...... https://skunk2.com/products/dave-talks-cams-part-2/
PART3...... https://skunk2.com/products/dave-talks-cams-part-3/
PART4..…. https://skunk2.com/products/dave-talks-cams-part-4/