Flowmaster's mufflers use...
Flowmaster's mufflers use a baffled design to dissipate each pressure wave's energy before it exits the exhaust pipe.
Borla Performance Industries In racing circles, Borla is famous for its straight-pipe designs, which are popular in Dirt Late Model racing where big-inch engines require a lot of flow. Borla also stresses that it's as important to maintain exhaust gas velocity as it is to maintain flow because the velocity of the exhaust pulse is what helps create the scavenge effect in the combustion chamber. It's for this reason that the mufflers are designed to provide maximum flow characteristics with smaller diameter tubing. Borla offers a host of options in every size and length imaginable. Simply give Borla's tech department a call to determine what will work best with your engine.
Flowmaster Flowmaster mufflers use the baffled design to disrupt the sound-producing pressure waves before they exit your exhaust system. Like water rushing past a rock in a stream, the baffles produce low-pressure areas in the lee of the exhaust flow, which deaden sound. Flowmaster's line of racing mufflers is designed to maximize the scavenging effect while minimizing the overall package size of the muffler so that it can easily be placed in the best location under your race car.
This cutaway shows Spin Tech's...
This cutaway shows Spin Tech's unique muffler design, which forces the exhaust gasses into vortices that "trap" the noise.
Schoenfeld Headers Famous for their headers for years, Schoenfeld also produces a line of mufflers specifically for racers. Constructed from mild steel and economically priced, Schoenfeld's mufflers utilize the straight-pipe design without packing material for minimum weight, size, and cost. If you race IMCA, SUPR, All-Stars, WoO, or any of several other sanctions, Schoenfeld produces mufflers specific to your rule book. Also, if your rule book requires only a muffler without stating noise limits, Schoenfeld produces a lightweight muffler insert that fits in your header's collector and produces limited damage to your power and your checkbook.
Spin Tech Spin Tech uses a unique baffled design to "spin" the exhaust gasses into several high-velocity vortices, which are said to "trap" the sound waves. This is accomplished with several specially designed tubes welded into place inside the muffler. Spin Tech says the effect is essentially to turn the sound into heat and radiate it out through the muffler case. The vortices are also said to create low-pressure systems inside the case, which improve combustion chamber scavenging.
Engine Tuning for Mufflers
Obviously, every situation is different, but here are a few guidelines for engine tuning when adding mufflers to the exhaust system.
Although it has recently begun...
Although it has recently begun producing street mufflers, Spin Tech's bread-and-butter is racing. It has several designs available depending on the class you are racing and the decibel levels you are required to meet.
Although it's advantageous in any situation, make sure you run a crossover pipe between the exhaust pipes before the mufflers. This helps equalize pressure between the cylinder banks, which can help with pulse dampening and reduce noise even without a muffler. Of course, a crossover pipe increases scavenging and helps power, so you should be running one anyway. Both X- and H-pipe designs work well.
Here's an obvious one for you: Don't overmuffle. If your rule book states specific decibel limits at a specific distance, find a muffler that meets that requirement with your engine without going over. Don't make yourself work harder than you have to.
If you are forced to use a spec muffler that increases backpressure, keep an eye on your coolant and oil temps. Backpressure not only reduces exhaust gas flow out of the combustion chambers, but also causes the engine to retain more heat.
Backpressure harms an engine's fuel economy. Also, additional jetting in the carburetor may be required to regain a measure of lost performance.
If you have a muffler that adds to backpressure, you may be required to make a cam change to restore some of the lost power. Typically, you will need to shorten the valve overlap.
Don't end the exhaust circuit at the muffler. In most cases, a length of exhaust pipe after the muffler will increase power and sound dampening.
Finally, if you are running a Street Stock on another low-power class, your engine's limited exhaust flow means you probably don't need a full-out racing muffler. If money is an issue, a race muffler may provide no benefit over a performance street muffler. Try one out and see, or ask your engine builder.