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.
|
|
More often than not, a gain in power by way of an exhaust upgrade
does nothing for fuel economy. However in this case Kevin was
able to consistently measure an improvement in both EPA methods
described earlier.
2006 Mustang V6 Exhaust Test
|
|
City
MPG
|
Hwy
MPG
|
HP
Peak
|
TQ
Peak
|
Stock |
21.71
|
28.22
|
181
|
187
|
Flowmaster |
22.34
|
29.24
|
189
|
191
|
Gain
|
+.63
|
+1.02
|
+6
|
+4
|
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. 
|