This is a collection of information regarding Intake design, that will shed some light for folks on why Nissan is using low volume, long runner intake designs.
The short answer is for low end torque and engine response, improved idle quality and usable power where most folks want it. The reasons are below:
Stock intake manifolds are often a compilation of compromises. Stock manifolds are typically designed to minimize manufacturing cost, to accommodate emissions fittings, to fit a tight engine compartment with limited hood clearance, and to provide good low to mid-range performance, fuel economy and emissions. Most stock engines spend 95 percent of their running time between idle and 3,000 rpm, with rare bursts above 5,000 rpm.
Is Bigger Better?
The plenum in a stock manifold is typically smaller to keep air velocity high. Likewise, the cross-section of the runners is also small to keep the air moving at maximum speed into the cylinder ports. This provides good idle quality and throttle response, but also limits how much air the manifold can flow at higher engine speeds. Eventually the speed is reached at which the engine will try to pull in more air than the stock intake manifold can flow. That’s when the stock intake manifold needs to be upgraded to a performance manifold with a larger plenum and larger runners.
Runner Length
Runner length also affects the rpm range where an engine makes the most power. Longer runner lengths have a “ram” effect that helps keep the air moving forward as the intake valves open and shut. When an intake valve opens, there is a short lag before the cylinder starts to pull air through the runner into the combustion chamber. A longer runner helps maintain the inertia of the air column so it will fill the cylinder faster.
Information above comes from multiple sources (checked and double checked for accuracy), but the 2 paragraphs are directly from:Intake Manifolds: From Mild to Wild - Engine Builder Magazine
I couldn't have written it better, so I just borrowed it.
Also if you're interested in toying around with the numbers and science, this is a pretty cool calculator:
https://www.rbracing-rsr.com/runnertorquecalc.html
It's not all the parameters, but it'd give you a starting point.
The short answer is for low end torque and engine response, improved idle quality and usable power where most folks want it. The reasons are below:
Stock intake manifolds are often a compilation of compromises. Stock manifolds are typically designed to minimize manufacturing cost, to accommodate emissions fittings, to fit a tight engine compartment with limited hood clearance, and to provide good low to mid-range performance, fuel economy and emissions. Most stock engines spend 95 percent of their running time between idle and 3,000 rpm, with rare bursts above 5,000 rpm.
Is Bigger Better?
The plenum in a stock manifold is typically smaller to keep air velocity high. Likewise, the cross-section of the runners is also small to keep the air moving at maximum speed into the cylinder ports. This provides good idle quality and throttle response, but also limits how much air the manifold can flow at higher engine speeds. Eventually the speed is reached at which the engine will try to pull in more air than the stock intake manifold can flow. That’s when the stock intake manifold needs to be upgraded to a performance manifold with a larger plenum and larger runners.
Runner Length
Runner length also affects the rpm range where an engine makes the most power. Longer runner lengths have a “ram” effect that helps keep the air moving forward as the intake valves open and shut. When an intake valve opens, there is a short lag before the cylinder starts to pull air through the runner into the combustion chamber. A longer runner helps maintain the inertia of the air column so it will fill the cylinder faster.
Information above comes from multiple sources (checked and double checked for accuracy), but the 2 paragraphs are directly from:Intake Manifolds: From Mild to Wild - Engine Builder Magazine
I couldn't have written it better, so I just borrowed it.
Also if you're interested in toying around with the numbers and science, this is a pretty cool calculator:
https://www.rbracing-rsr.com/runnertorquecalc.html
It's not all the parameters, but it'd give you a starting point.