As cities grow and racetracks...
As cities grow and racetracks start to be closer and closer to the cities, mufflers will become more and more the norm and not the exception. Mufflers present a whole new set of issues. Just reducing noise does not always equate to a loss of power. When constructed as a system, a well-designed muffler can reduce sound without making your engine run like it's breathing through a restrictor. The real issue is that most racing headers were not designed to support the additional weight of a muffler, which can cause structural failure of the header even if the muffler has additional supports and brackets mounting it to the chassis.
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...
Notice the header on this Silver Crown car is a very typical four-into-one design. This is a very common collector used on 90 percent of the Sprint Cars in the country.
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...
The header on this Midget is different for a number of reasons. You'll notice that the collector is a two-into-one design. Two primaries are routed into one collector which is then routed into another collector. You will also notice that the pipe is chromed, which looks really great but many of the leading manufacturers of headers are not too excited about. This set of headers also has some volume added to the primary tube in the form of larger diameter tubes that run for several inches then revert back to the original tube size of the primary. This additional volume is an attempt to improve the scavenging effect of the header.
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...
The headers on this IMCA Modified have very short primaries and a short collector and muffler. This class of cars is very highly restricted when it comes to adjustability. But the opportunity for racers is that they have the opportunity to utilize different sets of headers to tune the car. If the rules are such that you can't make external adjustments, like having adjustable collectors, then changing the whole header may be another option.
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.