Q: A common question customers ask is, do race car mufflers cause torque or horsepower loss?
A: Short answer, yes, and no. Read on.
Horsepower comes from a math formula in the measurement of torque at a given RPM. Then these two numbers are then calculated -- torque x RPM / 5,252 -- to arrive at horsepower. If you don't have access to actual dyno testing, here are a couple of sites with horsepower calculators to give you at least a rough idea. Keep in mind many factors that affect horsepower like weather, temperature, humidity, elevation, and fuel type are is not factored in using these calculators.
- Calculator.net ( also has a more in-depth explanation on horsepower and torque )
- WallaceRacing.com ¼ Mile and ⅛ Mile.
- There are many more out there, search for horsepower calculator.
Any change that affects torque, up or down, at a certain RPM is affecting HP. That effect could change through the whole RPM range or just within a narrow band.
Now back to the question of a race muffler causing a loss of torque or horsepower.
The way that a muffler can cause a loss of torque/horsepower is by not being sized right as in too small a pipe causing back pressure or being too large a pipe causing a loss of velocity not allowing proper scavenging of the cylinders. But the most common way is using a restrictive ( also known as reactive ) design of muffler.
As every engine needs the right CFM of air intake to operate at its full potential, so does the exhaust system need the right CFM out. On the intake side, if not enough air, it starves, to large, and the velocity isn't there for the air/fuel mixture to do what it needs to do going into the cylinder—the same idea on the exhaust side of things. Rule of thumb is the muffler has to flow about the same CFM as the air intake CFM is to run right.
The term race car muffler is very vague. There are no requirements to meet before a muffler can be labeled a race car muffler. Look for a company that can show real dyno tests and other racers with similar engines or vehicles that are satisfied with the results of a particular muffler.
Many manufactures are selling low-cost race car and hi-performance mufflers' that even if they don't affect horsepower in the beginning, they usually won't hold up very long to the harsh environment racing and hi-performance use produces. Generally, it's the packing/noise insulation that fails first. If that happens, you're lucky your car will only get louder. If you're not so fortunate, the packing starts coming apart causing a restriction that will create a loss of horsepower and could have you chasing tuning issues before realizing it's a failing muffler.
We here at Extreme Mufflers have been designing and building race car and hi-performance exhaust mufflers for over 20 years. After all those years, we have numerous dyno and track tests along with customer feedback proving a properly designed and sized muffler will not produce any horsepower or torque losses while providing a reduction in noise ( dB levels). We have found in a lot of cases we were able to improve the torque mid-range due to the changes in exhaust velocity. In some cases, we have experienced as much 10 to 20 ft. lbs. of torque gain with just the installation of our racing mufflers.
We design & build what is called an abortion flow thru type of exhaust muffler. That means there are no restrictions or chambers to redirect the exhaust flow inside the muffler.
Any time you are redirecting or changing the direction of exhaust flow you are creating a restriction and a slow down of the exhaust velocity. Once the exhaust flow has slowed, it's almost impossible to speed it up. Restrictions cause horsepower and torque loss. In some cases, you'll see manufacturers recommending a larger muffler inlet and outlet to compensate. As an example: if your exhaust collector is 3" they will have you go to a 3.5" in trying to compensate for the restrictions in their mufflers.
There are three types of muffler design: reactive, absorption, and a combination.
Reactive design is another name for restrictive design. They have sound chambers and/or tubes to route the flow around inside. The advantage is they are quite. The disadvantage is power loss when compared to an absorptive type muffler with the same pipe size.
Absorption design mufflers are a straight thru flow that, when properly designed and sized don't cause power losses. The advantage is no power loss and usually a smaller lighter muffler. The disadvantage is they are louder than the restrictive/reactive type.
A muffler designed to be a combination of the two still boils down to being a restrictive muffler. Although not as much as a full reactive/restrictive design. The advantages are less power loss than a reactive type. The disadvantage is not getting full power potential over a full absorptive muffler.
Because the Extreme Muffler product line of race exhaust mufflers is designed primarily for the race car market, we only design and build abortion style mufflers with a 12-month warranty.
But that doesn't mean they won't work on high powered streetcars. Please take a look at the cars in our Photo Gallery of customer cars.