The headers on this car are...
The headers on this car are quite different from the headers on the one below, yet they are competing against one another in the same race.
There are specific components we expect to see on a race car, special paint/graphics, gutted interior, a rollcage, and, of course, tubular exhaust systems or headers. Anything less than a nice set of headers and we would be disappointed from both a technical and aesthetic perspective. Headers are not a convenience item, nor are they an aesthetic feature, there is power to be had using headers.
From the Saturday Night crowd, to the highest levels of motorsports you will not find many race cars without a finely tuned exhaust. The one thing that the Saturday night racer often misses, however, is just how important and tunable the headers on their cars really are. Not to mention the fact that they can improve power characteristics by "adjusting" the exhaust system on their car.
Many racers do not think of headers as adjustable. They bolt on a set and usually until there is a reason to take them off, they stay on the car; sad, but true. The point of the matter is if you view headers as just something you bolt on to direct exhaust away from the engine compartment, you are leaving speed on the table. By not taking advantage of the potential adjustability of the exhaust system on your car you will be letting the competition drive away from you.
Just because you have rules...
Just because you have rules that prevent the adjustment of the headers doesn't mean that you can't make changes in the type, style, and configuration of the headers in the search for power and driveability. Note the different header designs on the two IMCA-style modifieds on this page.
Now, there is a balance that we need to reach between performance, durability, and cost. Headers are a simple part, a flange bolted to the cylinder head, tubes welded to the flange, a collector welded to the tubes and a collector tube. In reality headers are a system made up of the aforementioned parts. How these parts work in harmony to create the right power your car needs is up to you to determine.
When you start using headers as a power adder and not just something to route exhaust away from the engine, things start to get a bit more complicated. Parameters like the length, diameter and the wall thickness of the tubing, how the pipes are routed, are header pipes equal length, and does that really matter? The type of collector, the length of the collector, the material the headers are made from, and how they are welded together. These are all points that you need to look into when designing or selecting a set of headers for your race car.
In addition to the physical make up of the headers there are also some other dynamics to consider. Temperature, pressure, and sonic energy are all involved in helping the header system make power. If the primary job of headers were to just move the exhaust out of the engine compartment, a cast-iron manifold would work just fine. But we have a higher need. We need the header to help extract the exhaust out of the cylinder.
It's clear that headers take...
It's clear that headers take up some room-even on semi-open-wheel cars the packaging can get a bit tight and require some compromises with the design of the header.
We all know that in a four-cycle engine the exhaust is pushed out during the exhaust stroke. The addition of header pipes is to establish a low pressure area outside the exhaust port so the header assists in extracting the exhaust from the cylinder. If we envision a running engine, the exhaust is exiting the exhaust port and enters the header as slugs of hot gas. As the exhaust pulses through the primary tube it creates a pressure pulse or spike. If we remember anything about weather, it is that wind is created when high pressure air moves into and toward a low pressure area. This slug of gas is above atmospheric pressure and, at first, the heat and the pressure of the combustion process is going to start the movement (pushing) of the exhaust gasses out of the port. The role of the header is to minimize the energy that is being placed on the engine to push these gasses out of the cylinder as the pressure from the combustion process starts to wane. In essence, the header creates power by reducing the need for more power to move the piston up into the chamber during the start of the next cycle.
Ideally, the headers should extract all of the exhaust gasses out of the cylinder and help create a lower atmospheric pressure in the cylinder before the intake valve opens. This will aid in filling the cylinder when the intake valve starts to open and the intake charge flows into the cylinder. This pull or extraction is a combination of the low pressure area that is caused when the high pressure slug of gas moves down the header or primary pipe. Once the slug of gasses reaches the collector, the flow and pulses of the other cylinders will further help to extract the exhaust gasses.