This provides good idle quality and throttle response, but also limits how much air the manifold can flow at higher engine speeds.Įventually the speed is reached at which the engine will try to pull in more air than the stock intake manifold can flow. Likewise, the cross-section of the runners is also small to keep the air moving at maximum speed into the cylinder ports. The plenum in a stock manifold is typically smaller to keep air velocity high. Even so, a well-designed single-plane manifold will almost always outperform a split-plenum dual-plane manifold from 2,500 rpm and up. This makes a significant improvement in mid-range and high rpm power, but may sacrifice some low-end throttle response and torque. Opening up the plenum allows all of the cylinders to pull from all the barrels in the carburetor or throttle body for more airflow at higher engine speeds. These types of manifolds can be a good choice for heavier vehicles with automatic transmissions, stock gearing and engines that won’t rev much beyond 5,500 to 6,500 rpm.īut if an engine has a longer duration camshaft, stiffer valve springs, bigger cylinder heads and gearing for revving to 7,500 to 8,500 rpm or higher, an intake manifold with an open plenum, single-plane or “360 degree” configuration is usually the best choice. 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. 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.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |