A performance manifold that is designed for a street application will often retain the split-plenum or dual-plane design for this same reason. This design, though wearing the “stock” label, isn’t necessarily bad. The reason for doing this is to keep intake runner velocity high so the cylinders will fill quickly and produce maximum power and torque at low- to mid-range rpm. The intake manifold essentially splits the V8 engine into two V4s. Four of the cylinders (two on each side) draw from one of the primary barrels in the carburetor, and the remaining four cylinders draw from the other primary barrel. On a V8 engine with a two-barrel or four-barrel carburetor, most stock manifolds have a split-plenum, dual-plane or “180 degree” configuration. But if the engine is being modified to make more power, the stock manifold usually runs out of air above 5,000 rpm and becomes a restriction. In fact, each will usually out-perform most aftermarket manifolds at lower engine speeds. Most stock engines spend 95% of their running time between idle and 3,000 rpm, with rare bursts above 5,000 rpm.Ĭonsequently, if the engine is modified with a hotter camshaft, larger carburetor or throttle body, and/or bigger heads, the stock manifold will usually run out of air above its original design speed and hinder power rather than build power.Īs an example, the stock intake manifold on a Chevy 5.7L with tuned port injection, or the one on a stock Ford 4.6L V8 are both well designed for low to mid-range torque and power. 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. Stock intake manifolds are often a compilation of compromises. The part bypassing the core, and providing only thrust by fan acceleration is 419 kg/s.įor comparison the Trent XWB (A350 XWB), a larger engine developing 430 kN at takeoff, has an air mass flow of 1,440 kg/s ( source).A well-designed manifold that is properly matched to the engine’s requirements will make more torque and horsepower than a manifold which is mismatched to the engine. The part used in the core for combustion, bleed air and core cooling is 485/7.4 = 66 kg/s This is supported by figures found online in non authoritative sources, like page 245 of this book:Īfter the fan, air is separated in two flows: core (hot/primary) and bypass (cold/secondary) according to the bypass ratio. So we can roughly estimate air mass flow in cruise to be about 485 * 0.22 = 107 kg/s. (meaning cruise at 27% T/O thrust requires 22% of the T/O fuel, the engine is more efficient in altitude.) T/O thrust is 150 kN, fuel consumption 2.3 kg/s.It can be assumed relatively safely that air is in proportion of fuel.Īccording to this document, for the CFM56-5C: I don't have the actual figure but we can do a quick estimate using the fuel consumption. A A340 has four engines.įortunately this thrust is not needed after takeoff and the engine airflow is considerably lower in cruise. It has an air mass flow of 485 kg/s ( source). The CFM56-5C, the largest CFM56, powers A340.
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