Will I Gain More Horsepower With An Exhaust System?
After-market exhaust systems are almost always less restrictive than factory exhaust systems. However, that doesn’t mean that adding an after-market exhaust will always result in more power. Depending upon your vehicle and the system you choose, an after-market exhaust can add as much as 50 horsepower or as little as 2 or 3 horsepower. Here’s how you can figure out what to expect:
Don’t Focus On Horsepower Only
Horsepower is calculated by multiplying torque by RPM. Therefore, if a new exhaust system adds just 10 lb-ft of torque at 5,000 RPM, that will result in a horsepower increase of 9.5 hp. While that might sound like a solid horsepower gain, an extra 10 lb-ft of torque at 5,000 RPM usually doesn’t do you a whole lot of good in day-to-day driving. After all, how many of us run our engines at 5,000 RPM on a constant basis?
Throw Exhaust System Manufacturer Estimates Out the Window
Because horsepower is a function of RPM, it’s very easy to show big horsepower gains on paper. Diesel trucks are a great example – because they generate gobs of torque anyways, adding an extra 35 lb-ft of torque at 3,300 RPM results in a gain of 23hp. This number may seem impressive, but an extra 35 lb-ft of torque at 3,300 RPM isn’t that useful to your typical diesel truck owner. It’s a good increase to be sure, but it’s not usable power.
The other reason that you shouldn’t put a lot of stock in manufacturer estimates is that dyno results are fairly easy to manipulate. When a vehicle is tested on a dyno, there can be significant variations from test to test without any change to the engine. If a manufacturer takes their worst run from their “before” tests and their best from “after” tests, they can show a really big gain that’s mostly due to normal variations between runs.
In other words, exhaust system performance estimates are always very generous. If the kit from Flowmaster supposedly adds 8 hp and the kit from Magnaflow supposedly adds 13 hp (or vice versa), chances are good that both perform pretty close to the same.
The Most You Can Gain is 2-5%
If you want to know how much power you can expect to gain from adding an exhaust system to your car, assume that your engine will get 2-5% more powerful. More specifically, large engines like a big 6.0L V8 typically see about a 2%-3% horsepower increase. Smaller engines, like a 1.8L 4-cylinder, typically see a 3-5% horsepower increase.
HOWEVER, exhaust systems have a multiplying effect if you combine them with other add-ons. The exhaust system by itself won’t add a lot of power, but combined with an air intake and a performance chip or power programmer you could see a significant increase in performance. You’ll also see a slight increase in fuel economy (assuming you keep your foot out of it, of course).
Remember That The Intangibles Have A Value
Adding an after-market exhaust system to your vehicle isn’t just about adding some more horsepower or improving fuel economy. You’ll enjoy a sportier exhaust note, better throttle response, and hopefully driving will be just a little more fun.
Considering how inexpensive an after-market muffler is, it’s a nice way to customize your vehicle on a budget. The icing on the cake is slightly more power and improved fuel economy.