Re: Short vs Long Tube Headers
here is an interesting read from sanderson headers
Sanderson Headers :: Let's Get Technical
Let's Get Technical
Let's Get Technical
Sanderson Header Tech"Even if you're running a radical cam and a blower, you're better off sizing your headers smaller ... unless you do most of your driving at full throttle."
It's no secret that a good set of headers is one of your best performance investments. In fact, most engine builders say that headers are one of the first things you should change to when modifying your motor. But before you plunk down your cash, remember that a couple factors determine what's going to work best for your particular application.
The first thing to consider is the intended use of your vehicle. 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 (size) of the engine plus any other serious modifications and power-adders (camshaft, blower/supercharger, cylinder heads, nitrous, etc.) are equally important factors.
Stock manifolds are mass produced and are designed to clear all the accessories offered for any vehicle the engine 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 common misconceptions. First is the size of the primary tube. It's easy to assume the bigger the tube the better, but that's not the case.
The fact is, primary tubes that are too large actually cost you torque and horsepower by slowing down the rate at which the exhaust gases travel through the system. Think of your engine as an air pump. Every time the exhaust leaves the combustion chamber it is being forced into the primary tube for that cylinder.
Horsepower and Torque as a function of header tube diameter
Smaller diameter pipes flow less volume than larger ones, but the exhaust in the smaller pipe flows faster. Until you reach the RPM where the sheer volume of exhaust gases require bigger primary tube diameters, smaller tubes will scavenge the cylinders more efficiently. If you're using the engine in the 1,500 to 3,500 RPM range, which is typical for a street-driven vehicle, you definitely want 1-1/2" to 1-5/8" primary tubes for any small block and 1-3/4" to 1-7/8" for a big block engine. Any bigger and you'll lose a considerable amount of low end torque. beyond 3,500 RPM it is a question of where you want the power peaks. As you can see from the charts on this page, small tube headers do not lose their edge in horsepower and torque until you exceed 5,500 RPM.
Even if you're running a radical camshaft 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.
The second biggest controversy in header design is the "equal length" versus "shorty" styles - which is best? Like most performance products, there are advantages and disadvantages to both.
Exhaust headers with equal length tubes have been shown to develop slightly more power on an open exhaust 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 expensive 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 be more easily 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 become 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. Plus, Sanderson headers provide excellent clearance around spark plugs, starter and chassis components, as well as ground clearance for lowered vehicles. The charts on this page illustrate just how little power you trade off for the much lower cost and easy installation of compact headers.