Best of Both Worlds (continued)

To measure the fuel consumed during each drive the car, a flow-meter is installed in the fuel line. This meter consists of a precision, unidirectional, vane capable of measuring the amount of fuel flowing past it. Consequently it breaks up one gallon of fuel into 3600 units. The number of units are measured during each drive cycle, then converted back into gallons to determine the fuel economy.

After baselining the city and freeway loops with the stock muffler, the Flowmaster muffler was installed and the drive tests repeated. Installing the single muffler can be performed in about 20 minutes and no welding or cutting of pipes is necessary.

The dyno testing utilizes a method known as "carbon balance equation." The vehicle is placed on the chassis dynamometer and the coefficient of drag adjusted to match that which would occur on the road at 55mph. The vehicle is run for three five-minute segments, each at 35, 55, and 75 mph. This entire process is repeated twice, with one-minute cool downs in between.

The amount of CO, CO2 and 02 emitted through the exhaust is measured and plugged into an equation from which the fuel consumption and fuel economy are calculated.

Results
The results were quite interesting. The V6 Mustang gained horsepower and torque across the board, which is enough to cheer about. In comparison, the '05-'07 Mustang GT does not gain a lick from an aftermarket set of mufflers (see our 'Sound Thinking' article.)

Kevin installed a pressure gauge in the intermediate exhaust piping to measure back pressure. Interestingly, the back pressure with the stock muffler is over 7 psi. With the American Thunder muffler, peak back pressure is reduced to 1.6 psi. Kevin points out that there really is no magic back pressure number, and that the key is to maintain velocity. "You can put a 4" pipe on and have zero back pressure. However velocity will be very poor and you will lose torque," remarks Kevin. In the chart below, torque is up over 5-7 lb.ft. throughout the entire curve.

Torque           Horsepower The Green Line The green lines represent back pressure, and unlike horsepower and torque, the higher green line is not good. Notice with the factory muffler, backpressure (pressure measured in the pipe before the muffler) climbs to 7 psi. The Flowmaster 70-series muffler designed for the V6 Mustang drops backpressure to below 2 psi.

While the horsepower and torque gains are easy to appreciate, it is easy to dismiss the fuel economy results at first glance. After all, who pays attention to half, or even one, mile per gallon? Though, maybe more people do care about the slightest increase since gas prices are now the highest ever on record. However, put the numbers in perspective. Over the course of a 15 gallon (confirm V6 gas tank capacity) fill-up, that is an equal number of extra miles you can drive without filling up the tank. That amounts to a savings of about the cost of a gallon of fuel. Considering you are likely to fill up your tank 30 to 40 times per year, that is a $100. Not many aftermarket products pay for themselves in two years - let alone continue to put money back in your wallet.

Kevin tells us that not all their systems show such gains, but they are continuing to expand their testing to other vehicles. So far they have identified the most gains on trucks when under load. In particular, the F150 and F250 when towing show gains as high as 3 mpg with a Flowmaster system.