This Dynatech muffler is called...
This Dynatech muffler is called a Splitflow. Notice the divider in the pipe. This presents minimum restriction while breaking up some of the noise events.
If your track rules specify the use of a muffler, but no decibel limit is listed, then get one of the short, straight-through types that offer virtually no restriction. All you need to do is put these on the ends of the collectors.
No story on mufflers would be complete without discussing some of the ways to get the exhaust to the muffler. We are not speaking about headers or cast manifolds. We'll hold that topic for another time. What we are going to be examining is how the exhaust is fed to the muffler(s).
I called a friend, Greg Fuesler, who has exhausted this subject with Dynatech (pun intended). My questions concerned the use of x pipe systems,Y pipes, and H pipes, among other things. Fuesler's thoughts are incorporated into the rest of this article.
This Y pipe connects to crossover...
This Y pipe connects to crossover headers. Only one muffler is used in this system. This system works very well on tracks 51/48 mile and shorter. The Y system itself somewhat muffles the engine noise by its blending. Use 3-inch diameter pipe for engines under the low to mid-500hp range. For engines exceeding the aforementioned horsepower range, the use of 311/42-inch pipe will show a power benefit. Be realistic in estimating your horsepower.
It seems there is no single exhaust system that is correct for all applications. When class rules restrict the use of any type of side-to-side connection, then a straight-through muffler attached to each collector is thought to be best. There is some extra power available when you connect the two sides of a V-8 exhaust. In some cases, you may want to bring both collectors into one muffler. This applies to engines at the 525-550hp range or less. Also, you want to stay with 3-inch diameter pipes and the matching muffler. These sizes maintain the speed of the exhaust flow.
Higher horsepower engines running on tracks longer than a 11/42 mile can take advantage of 311/42-inch diameter pipes.
Where the Y pipe arrangement is not practical, such as in crossover headers, there are other solutions that can work just as well. The crossover headers have the left-bank cross behind the distributor to join in a Y with the right bank. If stock firewalls are required, these can't be used because the crossover pipes must go through the firewall.
The x pipe system or H pipe arrangement allows the exhaust system to possibly be placed more efficiently in the chassis, usually under the car. Both of these systems function virtually the same. The nature of the H pipes is not to change the flow between the two sides, but to allow the pressure waves to equalize. The size of the H crossover pipe is not too critical; however, it would be preferable to have it the same diameter as the collector.
For the H pipe to be most effective, it should be attached to the collector close to the point where the individual pipes come together.
H Pipe ArrangementThis is...
H Pipe ArrangementThis is the way an H pipe works: The H contributes little to exhaust flow, but contributes greatly to the exchange of exhaust pressure waves. The closer the H is located to the point where the primary pipes enter the collector, the better. The H would ideally be the same diameter as the collector, but the size in not critical. An x pipe system works in a similar fashion. Both the x pipe system and H pipe arrangement assist in noise reduction and also have power benefits. This might make it easier to find the right muffler to meet track decibel rules.
With the x pipe system, the two sides are brought together and then apart in an x shape. There can be some easy crossing of the exhaust pulses from one to another, which happens if an exhaust pulse reaches the x and finds a lower pressure on the other side. Still, its primary function is to equalize the pressure waves between both sides of the engine's exhaust.
The mufflers can be mounted anywhere in the system, but are probably more effective near the end of any exhaust pipe. Exhaust pipe length can be adjusted for the desired power range. While it is more effective to change header primary pipes to change the power range, it can be far easier to make the changes with the exhaust pipe length. Longer tubes provide more torque, which may work well on bullring tracks.
Another trick you might use for a track that requires a low decibel rating is to have the exhaust terminate far under the car. This will break up some of the noise events.
Noise is a fact of life in a race car. Controlling it is up to the racer, just like chassis setup. The more you know, the better you can race.