The headers on this car are quite different from the headers on the one below, yet they ar
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 that prevent the adjustment of the headers doesn't mean that y
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 up some room-even on semi-open-wheel cars the packaging can g
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.
With the bodywork removed it's much easier to see the type and size of the headers on this
You may have noticed on many race cars the headers are insulated or wrapped in special heat-resistant tape. While the reasons for the insulation may be varied, the best reason to insulate the headers is to keep the tubes as hot as possible. The hot pipe keeps more of the energy in the exhaust flow and in turn assists the headers' ability to work by keeping the exhaust gas moving and not giving up energy to the surrounding metal. We need to remember that the exhaust still has a significant amount of energy. In the form of latent heat, this kinetic energy is an important part of improving the power of the engine.
So, we have this wave of pressure and heat that is traveling down the pipe at a given speed that will be somewhat proportional to the speed or rpm of the engine (which varies with the power levels). We also have a wave of sound energy that is exiting from the exhaust port, but this wave is traveling at a speed that is significantly higher than the slug of gas and the pressure that accompanies the gas.
We need to remember that we have many different engine components that will have a marked effect on the exhaust flow-displacement, intake efficiency, combustion efficiency, exhaust port flow characteristics, camshaft profile, compression, and target rpms. These will all have an impact on the optimal design of the headers.
Viva La Difference. You will notice how different the headers are on this car.
From an engineering perspective there are many calculations and design work that can be accomplished to help you reach an optimum pipe and pipe length for a given rpm and combustion scenario. Unfortunately, racing engines, especially the poppet valve-type engines, operate over a broad rpm and load range. Achieving the optimum may be a great engineering exercise but we need a set of headers that will work over a broader range than the set we may design on our computer. Understanding how the headers work will help us to make more intelligent decisions when it comes to adjusting or tuning headers.
Mild versus Stainless
Let's look at the materials used to manufacture the headers. Will you use mild steel or stainless steel? For the majority of the Saturday night racers they will pick headers made from mild steel from purely a cost perspective.
From a power perspective, two headers with exactly the same physical dimensions, one made from mild steel and the other made from stainless steel will not show an appreciable power difference. There is nothing magical about stainless steel. It is more durable and better able to cope with the temperature and the physical demands of racing over the mild steel header, but if you are racing in a fairly restricted class like a Hobby Stock it doesn't make sense to have a set of headers that cost more than the car.
The primary tubes are larger and longer. The layout is very different. Notice how long the
Stainless steel headers will elevate your costs into the several-thousand-dollar range, versus several hundred for mild steel. In addition to raw material cost, stainless steel headers require different manufacturing processes which are traditionally more costly. So you have to employ some common sense when making material decisions. The use of headers fabricated out of mild steel for the Saturday night racer makes a great deal of sense, especially from a economic perspective.
Diameter And Length
When working on the pipes, you have to determine not only the diameter but the length. The goal should be to make the primary tubes as close to the same length as possible; this is sometimes difficult due to space in the engine compartment. Sometimes, the type of car the header will be in determines just how long the primary tubes can really be.
Other questions include, will they have a merged or a stamped collector? And how long will the collector be? It's not as easy or as simple as the completed product looks. All of these features can and do affect the power the engine produces and the shape of the power curve, which is what the racer will want to be able to affect by his adjustments.
Talk with your chosen header manufacturer about different options. You'll find that they are a wealth of knowledge when it comes to picking out or designing a set of headers.
As cities grow and racetracks start to be closer and closer to the cities, mufflers will b
One set of headers will never be optimal for every situation or track size. Your track's configuration dictates not only setups but also the type of power (hp versus torque) you need to get the car around the track the fastest. Many times power can be improved by fine-tuning the exhaust system. Just as a good chassis man can help you optimize the handling by developing a balanced chassis package, adjusting your headers can work in conjunction with the chassis to get your car off the corner or down the straight with greater speed and better driveability.
How can a properly tuned exhaust help you car have better driveability? If your car is producing wheelspin off the corners and is running out of power down the straights you may be able to adjust the power by utilizing a set of headers with larger primary tubes and a different length collector. Changing to a different set of headers may help you match the torque characteristics of your engine to the track helping you get off of the corner and down the straight better, thus smoothing out the power band, making the car easier to drive, and subsequently faster.
Notice the header on this Silver Crown car is a very typical four-into-one design. This is
This is especially true if you are running in a class that requires or has extensive engine restrictions. In reality for most Saturday night racers, the engine rpm levels very seldom exceed 6,000 to 6,500 rpm. This lower engine speed really lends itself to developing good measurable gains and tunability from a good set of headers. The Saturday night racer can really benefit from having multiple sets of headers and collector extensions to tune his exhaust. If you are not trying to optimize the exhaust on your car you are probably leaving horsepower and torque on the table.
So given what we have just learned, what should the racer be doing to use headers to tune the car? If you race in a class that does not allow you to play with your headers by adjusting the length or the size of the collector-IMCA Modifieds, for example-it makes sense to have a couple sets of headers that have different-sized primary tubes. Ideally, you should have primary tubes that range in size, (diameter) from 1 5/8, 1 7/8, 2, and 2 1/4 inches. This is especially true if you race at multiple tracks or the track conditions change appreciably at your home track.
The header on this Midget is different for a number of reasons. You'll notice that the col
The larger the tube diameter will usually have the effect of reducing the engine's torque at lower engine speeds and giving the engine a bit more torque at higher rpm. Depending on the track and track conditions such as a heavy dirt track or a slippery pavement track, this may equate to getting off the corner better. If you have your engines built by a professional engine builder, it makes sense to spend some time talking with him about the data he has gathered about your particular engine and how different style headers relate to the track or tracks your race.
A little planning at the shop can go a long way at the track when it comes to making changes in your exhaust systems. Look at ways to make changing headers a simpler task. Use studs and nuts on the two end bolt holes so you have a way to quickly mount the headers so you are not trying to accomplish a three-hand job with just two hands. Use some high-temperature silicone seal to glue the gaskets onto the headers at home so the gaskets are already on the headers and they are ready to use. You will still have to change the gaskets when you remove the headers but the assembly process will go much easier.
The headers on this IMCA Modified have very short primaries and a short collector and muff
You should be experimenting with different length collectors. Many header builders offer kits that will allow you to adjust your collector lengths with a simple bolt on extension which cost between $20 to $40 a set. It's surprising just how much of a difference they can make in how the car responds to collector length changes.
When you are looking at headers, it's important to try to get headers where the primary tubes are as close to the same length as possible. If you start to have differences in the primary lengths greater than 2 inches, you may see some differences in the headers' ability to scavenge as well as they would if the tubes are closer to the same length. There are some arguments about how important it is to have the primary tube be equal length. When you start talking to header manufactures who are building headers for top-level racers you will find that they make every effort to get the primary tubes as close to the same length as possible.
For the Saturday night racer, being able to make incremental adjustments in your exhaust system to suit the conditions at the racetrack can, and will, pay bigger dividends.