A lot of car enthusiasts love the idea of upgrading to bigger exhaust pipes because they believe that bigger is always better. While there are some situations where this is true, most of the time it's not. Read on to learn why.

Greddy exhaust
Is this Greddy Civic cat-back exhaust the right unit for your car, or should you build your own mega-sized exhaust instead?

Exhaust Pipes: Why Size Matters

The main reason people expand the size of their exhaust pipes is because they want more power, and they assume that exhaust gases flow like water in a pipe. While it's true that exhaust gases flow out of the engine faster in a bigger pipe, it doesn't "free up" the engine like many believe. Restriction is often a good thing.

While bigger exhausts can be better in racing - where engines spend most of their time at wide-open-throttle and high RPMS - most street cars are better off with an exhaust size the same size as a factory setup. The reasons are simple:

  1. When you increase the size of your vehicle's exhaust tubing, you change the velocity of the gas leaving the cylinder head.
  2. The speed of the gases is optimized by the engine designers so that it can facilitate something called "scavenging."
  3. Scavenging is basically an advanced fluid mechanics "trick" that basically uses hot exhaust gases to "suck" air into the engine cylinders.
  4. The faster that clean air is pulled into an engine cylinder, the better the air mix and the efficiency. This means the car makes more power.

Basically, the exhaust tubing on your Civic was designed to maximize scavenging effects, which maximizes horsepower.

Street Cars Can Lose Power With Big Diameter Exhaust Systems

If you replace an OEM exhaust system with a big diameter exhaust system, you reduce the amount of scavenging at lower RPMs. This is because a larger diameter system slows down exhaust gases at low RPMs. Lower speed exhaust leads to less scavenging at lower RPMs...which leads to decreased power on the street.

Magnaflow exhaust
A right-sized aftermarket exhaust system like this one from Magnaflow will usually be the same size as the OEM exhaust system, or just a bit bigger.

Big exhaust pipes cause your exhaust gases to expand. As they expand, they cool. As they cool, they slow down. The more exhaust your engine produces, the less the gas expands. The less it expands, the less it cools, and the faster it goes.

So, basically, bigger exhaust means more power at high RPMs, and less power at low RPMs.

Since most street cars spend their time at lower RPMs, an oversized exhaust will decrease power output at lower speeds. Often times, the car will perform better at high RPMS with an oversized exhaust, but you won't really notice it during normal driving.

Right-Size Your Exhaust Upgrades

Because performance suffers when exhaust size grows too big, it's important to get an exhaust system that's either the same size as OEM or slightly larger.

Often times, the best idea is to buy a tuned cat-back exhaust system from a well-known brand. We sell a large number of tuned cat-back exhaust systems for the Civic, almost all of which are dyno tested and proven to increase power.

Injen exhaust
This Injen axle-back exhaust is basically just a replacement muffler. It's very affordable, and increases power despite having a low cost. It sounds great too!

If a cat-back system isn't in the budget, consider replacing your Civic's muffler only. The OEM muffler is usually a bit of a performance issue, as it's designed to be quiet rather than efficient. If you swap out an OEM muffler for an aftermarket performance unit, you'll get a better sound out of your car and a little bit of power too. And the cost? $200 is the most you can spend, and most mufflers are half that cost.

If you're looking for a way to make your exhaust look huge without hurting performance, consider replacing your exhaust tips. The exhaust tip size doesn’t affect your Civic’s performance, so you can go as big as you want here. Bigger tips are an easy way to add an aggressive look without decreasing performance, and they're very affordable too.

Recommended Exhaust System Brands

The following premium exhaust system brands offer performance exhaust systems that are already tuned for Civic engines:

Summing Up

In a nutshell, bigger isn't always better when it comes to upgrading your Civic's exhaust system. It's not about total horsepower as much as it is about day-to-day street performance. If you're not a racer, it's better to boost your Civic's speed from 0-60 than its speed on the race track.

Last, but not least, don't build your own exhaust system. It's too hard to create a system that matches the quality of either your OEM system or a tuned cat-back exhaust system from a reputable brand. DIY exhausts often use crush-bent pipe, which hurts performance quite a bit, and most DIY'ers oversize the tubing. Don't mess with it.

Instead of spending time and money trying to reinvent the wheel, just buy a good quality exhaust (or aftermarket muffler) and call it good.