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NES304
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« Reply #2 on: July 10, 2013, 11:19:01 AM » |
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Whoa, Can o worms there...
Copied from PACEMAKER SITE
What is the difference between headers and extractors?
None! In Australia, headers were known as extractors through the 60's and 70's by the pioneering companies that developed them. In America at the same time they were coined headers (also spelt hedders). This was in part due to the fact that they (headers) are an extension of the cylinder head. In the 80's new Australian companies, along with the established industry, began to market extractors as headers. The main reason being that these companies intended to change the image of the humble extractor to more of a common vehicle replacement component. Some 'old school' enthusiasts still call them extractors today.
What is the difference between a TRI-Y and a 4-into-1 design?
A 4-into-1 design is perhaps the most traditional design. This design is common to the US market and is well used within the drag race fraternity. The basic principle behind the design is that the scavenging effect within the collector cone effects the three remaining pipes (in a V8 half), instead of limiting the pulse to the very next pipe in the sequence. This generally results in a header that performs very well in the mid-range to top end of the engines performance.
A TRI-Y on the other hand splits the firing order evenly and uses the secondary pipes as sequential collectors. This results in generally a greater scavenging effect due to the fact that scavenging is achieved at 2 different points in the header design, firstly at the primary to the secondary collector and secondly to the secondary outlet collector. Generally this improves torque in the lower to mid range performance of the engine.
Both designs are usually more efficient than a standard manifold and both offer distinctly different advantages.
Why don't car companies fit them as standard?
There are two main reasons, firstly like all things, vehicles are made to a standard and a cost. The cast iron standard manifold will always be the cheapest way of producing an exhaust manifold. However, car manufacturers do know the benefits of a tubular designed exhaust headers and indeed generally do offer this type of product on a sports related sedan, eg. HSV, Tickford/FPV, etc. These tubular manifolds are still better than a standard manifold but are still limited to cost, and as such are a compromise in design.
Secondly, cast iron manifolds can be cast into awkward and different shapes to accommodate steering boxes, etc, and can be installed onto the engine along with all the other necessary bolt on components during engine assembly and with the engine still able to be slotted into the body during the vehicle build. Headers however will generally take on a different proportion and often can wind themselves around steering components, etc, which in turn would slow down the vehicle build time process.
How much increase in power will I get?
In most cases around 10% is quite achievable. This may mean if you have, for example, a 4WD vehicle delivering around 70 kilowatts at the wheels you could expect possibly 6 to 10 kilowatts increase. If you have a V8 5.7 Litre commodore with around 160 kilowatts at the rear wheels you could expect to reach 170 to 180 kilowatts. This is just a generalisation and other factors do become involved. Cold air intake and open exhaust systems encourage the full effect of a well designed set of headers.
Will headers make my car louder?
The simple answer to this is 'no'. Headers by nature do not increase the Db range by themselves. The main reason for any exhaust system to increase the sound level is found in the choice of mufflers. Car manufacturers choose to use very restrictive but sound efficient reverse flow mufflers. These mufflers are very effective in reducing noise levels but also are very restrictive in flow. Some after market mufflers are very good in producing a high flow rate while still remaining within the law. Other mufflers are just too small in shape or too big in pipe diameter to do the job of effectively quieting the vehicles emissions. All customers wishing to alter their vehicles exhaust system should check with their states regulatory authority and work with reputable exhaust shops. Headers however do deepen the sound of the note of the exhaust. Much like a flute, if the pulse travelling down the barrel is allowed to escape through the first hole a high pitch is audible, however if the same pulse is allowed to complete the journey to the end, a much deeper note is heard. Headers by their design will have longer tubes than a standard manifold, creating a deeper note.
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