Throttle Pressure and Throttle Response

From a technical point of view, throttle response can be measured by how fast your engine can build vacuum in its intake manifold, via throttle pressure. The faster and higher peak vacuum is reached in the intake manifold, the higher the pressure differential will be between outside air, and your engine. This pressure differential forces the air to flow from the area of high pressure (outside air) to the area of low pressure (the engine and cylinders), and the higher the pressure difference, the greater the pressure force, and the faster the air flow into the engine.

This is essentially how throttle response works. To improve throttle response several engine alterations can be used to achieve a higher peak vacuum in the engine or a faster change in vacuum per throttle input… some of these include:

1- Using undersized intake pipes and intake plenum runners to increase the airflow velocity in the intake system, making the engine able to suck all the air out of it faster and create vacuum sooner.

2- Adjusting intake cam timing to open the intake valve as peak vacuum is created inside the cylinder near bottom dead center.

3- Reducing the overall intake system volume, by using smaller manifolds, less vacuum lines, and more electrically operated (rather than vacuum operated) engine auxiliaries which means the engine has less air volume to clear from the intake system to create a vacuum in the manifold to force new air in. 

4- Using cam separation and cam overlap (when both intake and exhaust valves are open at the same time) to have the previous cycle’s exhaust gasses help pull in fresh intake gasses for the beginning of this combustion cycle.

One interesting application of this concept is the G-Power supercharger kit for the BMW M3. The ASA supercharger powered kit focuses on response and efficiency rather than on astonishing peak power figures. The G-Power kit utilizes a very conservative boost supercharger by ASA giving a peak of only 4.4 psi of boost. Since the engine already very highly powered at 420hp, the addition of just 4.4psi of boost results in well over 500hp (as a conservative estimate) and as much as 560hp as a result of this combination. 

The focus of the G-Power kit is not just power figures, as rather than just providing a supercharger kit for the M3, G-Power has designed a completely new intake manifold for the M3. The manifold although has higher volume than the original M3 manifold (for more peak power as this is now a supercharged car), does have a narrow profile that promotes high air velocities to improve throttle response. Furthermore, the new manifold has integrated individual runners for each cylinders complete with trumpet style inlets raised from the floor of the plenum, which has been proven through fluid flow simulation to reduce boundary pressure differentials, reduce the pressure drop inside the intake manifold, and promote higher air velocities that lend themselves to higher peak vacuums and faster vacuum buildup inside the manifold. 

Even though centrifugal superchargers typically show a linear boost curve with engine rpm, and thus produce little to now power gain in lower rpms, the combination of this supercharger with the redesigned intake manifold and new tune reportedly provides over 20% increase in torque at ALL engine rpms, and with increased response. 

Here it is in G-Power’s own words:

Air duct: Sport air filter system, CAD-FEM flow optimized boost recooling system consisting of an air duct made from aluminum cast, high capacity air-to-air intercooler made from aluminum cast in the car’s front and a large volume air box made from aluminum cast, including 8 integral resonance induction pipes made from light polyamide, ensuring an optimal throttle response and a perfect torque curve; pneumatic controlled, engine load related boost control; boost level approx. 4 psi rel.   

The G-Power kit comes in 3 power ranges corresponding to 4, 6 and 7psi of boost. The 7psi kit with their full titanium exhaust is capable of peaking out over 580 hp with great response to match. Last but not least, the new G-Powered M3 is capable of doing a 0-124 mph 2 seconds faster than a factory M3, which at those speeds is about 20 car lengths of distance between the two cars. Moreover the G-Power with its unlimited speedometer will keep pulling all the way up to 223mph!