Supercharging provides charge motion on the intake side, independently of piston motion. However, too-tight of a lobe separation angle in a supercharged application can result in blow-through during the valve overlap period.
One thing with supercharged and turbocharged combinations, is that the heavily compressed intake charge loses velocity compared to a lighter, less-dense naturally aspirated charge. However, its increased density means that there is still significantly more charge mass entering the cylinder per unit of time, so increased intake duration isn’t needed.However, on the exhaust side, with the increase in charge mass trying to escape the cylinder, additional duration helps reduce the pumping losses, especially with centrifugal superchargers that shine at higher engine-RPM.
Turbocharging SpecificsTurbochargers are a unique animal which have confused many over the past decades. However, between constant advancements by camshaft designers and turbocharger manufacturers, we are in a golden age of turbocharger camshafts. Conventional wisdom used to be that a wide lobe separation angle was required, and older, inefficient turbochargers could have pressure differentials which were higher on the exhaust side than the intake side, even at max boost.
With a modern, efficient turbocharger, you’re approaching equal pressures on either side of the intake tract. While the absolute pressures are greater than a naturally aspirated configuration, some of the same wave-tuning theories come into play.
Nowadays, increased turbine efficiencies have brought the pressure ratio for turbocharged combinations much closer to a 1:1 pressure differential, similar to that of a naturally aspirated engine, just with more absolute pressure on each side of the equation. “We can use piston motion and some wave tuning to get charge motion at a lower velocity and with less valve timing,” Godbold explains.Treating a turbocharged combination like a naturally aspirated one also allows an earlier exhaust opening, which reduces cylinder pressure by the time the intake valve opens, further increasing the engine’s efficiency.
Nitrous Oxide InjectionRight off the bat, you may think that a nitrous oxide application and naturally aspirated application are identical. For the most part, that’s true, but there are a couple key differences which must be taken into account. The density of the intake charge is increased with the addition of gaseous nitrous oxide, as well as an additional fuel charge.The increased intake charge density requires enhanced exhaust scavenging in order to draw in the heavier charge. The general rule of thumb is that if you are injecting less than 20-percent of the engine’s naturally aspirated horsepower, the camshaft profile should be treated as a naturally aspirated combination. Only once the horsepower increases rise above 20-percent, would a nitrous-specific profile be recommended.Because nitrous has its largest gains low in the RPM range, the common school of thought is that the camshaft profile should help balance the powerband. This also reduces the notable stress on the components in the lower RPM range while assisting with traction. By adding exhaust duration, opening up the lobe separation angle, and adding intake duration, not only is cylinder pressure lowered but the engine’s powerband is raised.
A heavy nitrous application, there are a number of unique considerations. On the intake side, you have standard atmospheric pressure, but a heavier, denser intake charge that takes more effort to draw in. On the exhaust side, you have an significantly increased mass of exhaust gasses (over a naturally aspirated combination) needing to get out of the engine.
While we’ve been very general in our explanations, the reason for that is twofold. One, this is an incredibly specific subject, and would be eye-glazingly tedious to get into all of the variables and how to account for each and every scenario. Two, the subject matter itself is so extremely advanced, people far smarter can write books on the topic, and we’re limited to this single article for now. Besides, that’s what the tech team at Comp Cams is for. They can help point you towards the right camshaft profile, whether it’s on the shelf or a custom grind.