LilYellowZQ8
12-07-04, 08:59 PM
Written by Jedi Master.
It's no secret that a good set of headers is one of your best performance investments. In fact, most engine builders say headers are one of the first things you should change when you start modifying your motor. But before you plunk down your cash, remember that a couple of factors determine what's going to work best for your particular application.
First thing to consider is the intended use of your car. Are you building a daily driver, a sometimes bracket racer, or a dedicated quarter miler? The RPM range where you want the most torque, along with the displacement of the engine plus any other serious modifications (cam, blower, heads, etc.) are important factors. Stock manifolds are mass produced and are designed to clear all the accessories offered for any vehicle the block may go into. So naturally, performance is compromised by manufacturing requirements. Tubular headers are built for power and their design can be very specific. Let's look at how headers work, and clear up a couple of common misconceptions. First is the size of the primary tubes. it's easy to assume the bigger the tube the better, but that's not the case. Fact is, primaries that are too large actually cost you torque and horsepower by slowing down the rate at which the exhaust travels through the system.
Think of your engine as an air pump. Every time the exhaust leaves the combustion chamber, it's being forced into the primary tube for that cylinder.
Smaller diameter pipes flow less volume than large ones, but the exhaust in the smaller pipe flows faster. Until you reach the RPM where the sheer volume of exhaust gases require bigger primaries, smaller tubes scavenge far more efficiently. If you're using the engine in the 1,500-3,500 RPM range, which is typical for a street driven car, you definitely want 1- 1/2" to 1-5/8" primary tubes for a small block and 1-3/4" to 1-7/8" for a big block. Any bigger and you'll lose plenty of low end torque. Beyond 3,500 RPM it's a question of where you want the power peaks. Small tubes don't lose their edge in horsepower or torque until you get above 5,500 RPM.
Even if you're running a radical cam and blower, you're better off sizing your headers smaller rather than larger, unless you plan to do most of your driving at full throttle. The headers we build are sized correctly for even the most heavily modified street motors.
Exhaust headers with equal length tubes have been shown to develop slightly more power in an open system, but not when hooked up to a street system with mufflers. Fact is, most street motors with shorty headers will produce the same power as they would with equal length headers.
Equal length tubes can produce more power, but they have to be the right length for the specific motor at the RPM range where you want the power. What that means is lots of custom fabrication and dyno testing, which translates into lots of time and money.
For racing applications, the slight gain may justify the cost, but competition cars can more easily be built "around the engine" than street cars. When you're working within the confines of a given body style and chassis, with motor mounts, starter, steering linkage and accessories to think about, the way the headers fit becomes more important.
That's where the compact or "shorty" style header shines. You get a significant performance increase compared to stock exhaust manifolds, at an off-the-shelf price.
Why headers work is a topic full of hot rodders old wive's tales and myths. Headers can produce substancial amounts of power, with little or no negative effects on power output. They work so well in making power, they are a rare win-win modification. Installing headers on your project car is essential for serious power potential.
Stock exhaust manifolds utilize a crude cast iron log-type manifold. This type of manifold is used for 3 reasons- space, cost, and quick cold start catalytic converter light-off. A log-type stock manifold cannot take advantage of resonance tuning effect of the exiting exhaust gases.A stock manifold consists of a tube with stubby legs connecting the exhaust ports to the main tube. It merely dumps into the main pipe.
A header is an exhaust manifold fabricated from tubular sections of pipe. Full radius mandrel bends are preferred so the pipe's tight radiuses will not be crushed down restricting flow. Each individual exhaust port has its own seperate primary runner instead of merely dumping into the shared main pipe of a log manifold.
The equal length primary pipes converge at a single, large diameter point called a collector. The collector is then connected to the down-pipe, which leads to the rest of the exhaust system.
Headers make more power by primarily using resonance tuning to create a low pressure, reflected wave rarefaction pulse during the overlap period. The overlap period is the point in time when both the intake and exhaust valves are open at the same time for a few degrees of crankshaft rotation.
To work right, headers must exploit the inertial force of the exiting exhaust gas. This rapidly moving, high-mass, high pressure pulse creates a suction pulling, the exhaust gases out the cylinder head exhaust ports.The best tuners create headers that pull in as much fresh fuel/air mixture as possible during the overlap period, while using a low level vacuum or rarefaction utilizing acoustic energy to maintain this vacuum. This helps create the suction neccessary for optimal exiting of exhaust gases.
The way a header is tuned is much like how an organ pipe is tuned. Each primary pipe is tuned for each individual exhaust port. The optimal length used is the one needed for the primary pipe to have a fundamental note corresponding to the time when the exhaust valves opens.
Another advantage of headers is that they produce more power by reducing backpressure and by the long individual runners preventing the exhaust blast from one cylinder from blowing into the next cylinder, contaminating the charge on overlap.
As far as which type is better? Without going into the mathematics, 4-1 headers produce good top end power while while slightly reducing bottom end power. Most all out race engines utilize a 4-1 header becuase they spend little time below the middle of the power band. 4-2-1 headers are better for street engines These type headers are more common on street cars because they produce overall power and make a little less on the top end than do 4-1 headers.4-2-1 are also better for producing low end torque. Expect 5-10hp gains depending on the level of modifications.
It's no secret that a good set of headers is one of your best performance investments. In fact, most engine builders say headers are one of the first things you should change when you start modifying your motor. But before you plunk down your cash, remember that a couple of factors determine what's going to work best for your particular application.
First thing to consider is the intended use of your car. Are you building a daily driver, a sometimes bracket racer, or a dedicated quarter miler? The RPM range where you want the most torque, along with the displacement of the engine plus any other serious modifications (cam, blower, heads, etc.) are important factors. Stock manifolds are mass produced and are designed to clear all the accessories offered for any vehicle the block may go into. So naturally, performance is compromised by manufacturing requirements. Tubular headers are built for power and their design can be very specific. Let's look at how headers work, and clear up a couple of common misconceptions. First is the size of the primary tubes. it's easy to assume the bigger the tube the better, but that's not the case. Fact is, primaries that are too large actually cost you torque and horsepower by slowing down the rate at which the exhaust travels through the system.
Think of your engine as an air pump. Every time the exhaust leaves the combustion chamber, it's being forced into the primary tube for that cylinder.
Smaller diameter pipes flow less volume than large ones, but the exhaust in the smaller pipe flows faster. Until you reach the RPM where the sheer volume of exhaust gases require bigger primaries, smaller tubes scavenge far more efficiently. If you're using the engine in the 1,500-3,500 RPM range, which is typical for a street driven car, you definitely want 1- 1/2" to 1-5/8" primary tubes for a small block and 1-3/4" to 1-7/8" for a big block. Any bigger and you'll lose plenty of low end torque. Beyond 3,500 RPM it's a question of where you want the power peaks. Small tubes don't lose their edge in horsepower or torque until you get above 5,500 RPM.
Even if you're running a radical cam and blower, you're better off sizing your headers smaller rather than larger, unless you plan to do most of your driving at full throttle. The headers we build are sized correctly for even the most heavily modified street motors.
Exhaust headers with equal length tubes have been shown to develop slightly more power in an open system, but not when hooked up to a street system with mufflers. Fact is, most street motors with shorty headers will produce the same power as they would with equal length headers.
Equal length tubes can produce more power, but they have to be the right length for the specific motor at the RPM range where you want the power. What that means is lots of custom fabrication and dyno testing, which translates into lots of time and money.
For racing applications, the slight gain may justify the cost, but competition cars can more easily be built "around the engine" than street cars. When you're working within the confines of a given body style and chassis, with motor mounts, starter, steering linkage and accessories to think about, the way the headers fit becomes more important.
That's where the compact or "shorty" style header shines. You get a significant performance increase compared to stock exhaust manifolds, at an off-the-shelf price.
Why headers work is a topic full of hot rodders old wive's tales and myths. Headers can produce substancial amounts of power, with little or no negative effects on power output. They work so well in making power, they are a rare win-win modification. Installing headers on your project car is essential for serious power potential.
Stock exhaust manifolds utilize a crude cast iron log-type manifold. This type of manifold is used for 3 reasons- space, cost, and quick cold start catalytic converter light-off. A log-type stock manifold cannot take advantage of resonance tuning effect of the exiting exhaust gases.A stock manifold consists of a tube with stubby legs connecting the exhaust ports to the main tube. It merely dumps into the main pipe.
A header is an exhaust manifold fabricated from tubular sections of pipe. Full radius mandrel bends are preferred so the pipe's tight radiuses will not be crushed down restricting flow. Each individual exhaust port has its own seperate primary runner instead of merely dumping into the shared main pipe of a log manifold.
The equal length primary pipes converge at a single, large diameter point called a collector. The collector is then connected to the down-pipe, which leads to the rest of the exhaust system.
Headers make more power by primarily using resonance tuning to create a low pressure, reflected wave rarefaction pulse during the overlap period. The overlap period is the point in time when both the intake and exhaust valves are open at the same time for a few degrees of crankshaft rotation.
To work right, headers must exploit the inertial force of the exiting exhaust gas. This rapidly moving, high-mass, high pressure pulse creates a suction pulling, the exhaust gases out the cylinder head exhaust ports.The best tuners create headers that pull in as much fresh fuel/air mixture as possible during the overlap period, while using a low level vacuum or rarefaction utilizing acoustic energy to maintain this vacuum. This helps create the suction neccessary for optimal exiting of exhaust gases.
The way a header is tuned is much like how an organ pipe is tuned. Each primary pipe is tuned for each individual exhaust port. The optimal length used is the one needed for the primary pipe to have a fundamental note corresponding to the time when the exhaust valves opens.
Another advantage of headers is that they produce more power by reducing backpressure and by the long individual runners preventing the exhaust blast from one cylinder from blowing into the next cylinder, contaminating the charge on overlap.
As far as which type is better? Without going into the mathematics, 4-1 headers produce good top end power while while slightly reducing bottom end power. Most all out race engines utilize a 4-1 header becuase they spend little time below the middle of the power band. 4-2-1 headers are better for street engines These type headers are more common on street cars because they produce overall power and make a little less on the top end than do 4-1 headers.4-2-1 are also better for producing low end torque. Expect 5-10hp gains depending on the level of modifications.