Dyno Day 3
One of the most common modifications made to any enthusiast's vehicle is to the exhaust system; looking for more power, fuel economy and sound leads us to shuck the stock muffler and substitute an exhaust that flows more freely. Such modifications generally yield more noise, but increased horsepower and fuel economy do not always follow. After installation of a Gibson cat-back exhaust system on my Frontier I couldn't wait to get to the dyno to see if I'd gained any horsepower.
The exhaust note on the V-6 frontier is pretty nice for a stock system, but the Y-pipe that connects the catalytic converters to the muffler looks pretty restrictive (see pics of the stock exhaust here). The Y-pipe that came with the Gibson was much smoother, but I was a bit concerned that the entire system was built from 3" mandrel-bent pipe; I was afraid that such a large-diameter exhaust might actually cost me a bit of grunt on the low end of the power band. I watched with interest as we strapped the truck to the dyno and hit the gas...
You can see the results on the graphs below--The new exhaust added peak power gains of 5.7 horsepower and 5.7 ft/lbs torque. I was interested to note that these gains were evident pretty much across the power band and not just at the top end. Please don't make too much of the apparent differences at the very low end of the graphs; because this truck has an auto transmission we had to conduct the tests in 3rd gear, and we couldn't roll-on the power until about 36-3700 RPM. Given estimated driveline losses of about 20% for an automatic transmission, that yields 284 horsepower and 295 ft/lbs torque at the crankshaft--not too shabby for a "small" truck!