Many auto enthusiasts talk about improving their exhaust system with a cat-back kit or upgraded muffler, but not all of the people talking about these improvements really know how they work. The reason? Exhaust systems are deceptively simple. While it seems like a car’s tailpipe is the automotive equivalent of a downspout on a rain gutter, there’s actually quite a bit more to understand.
Exhaust 101 – An Engine is A Pump
Think of a car engine as a pump that takes air and fuel and turns it into motion, exhaust gases, and heat. At low RPMs (i.e. when a vehicle is idling), the pump isn’t producing much in the way of heat or exhaust. At wide open throttle (WOT), the engine is producing copious amounts of both…which brings us to a key concept in understanding exhaust systems. An exhaust system doesn’t just discharge the waste from the combustion process, it discharges the heated waste of the combustion process.
The other thing to understand about a vehicle exhaust system is that it gets rid of a very toxic mix of gases. While modern vehicles produce far less exhaust than ever before, given enough time they can still churn out a lethal amount of carbon monoxide. This means that your vehicle’s exhaust system must also transit the exhaust gases away from the passengers.
Heat Changes The Game
Without diving into the intricacies of thermodynamic theory, it’s safe to say that:
- Cold air is more dense than hot air
- As hot air travels down your exhaust pipe, it cools off
As a result, designing the perfect exhaust system is surprisingly difficult. You need a system that will carry the toxic gasses away from the passengers, but you also want to ensure that the exhaust gases don’t cool too quickly and become dense, as they’ll be harder to “push” out of the pipe and reduce the flow of the exhaust system.
Flow is important because engines, cylinder heads, and exhaust headers/manifolds are designed with a range of exhaust airflow velocities in mind. When the velocity of the exhaust gases matches the specification determined by the engine designer and engine tune, you get ideal exhaust flow. But if that velocity is too high or too low, you’ll get reduced performance.
Therefore, if you install a system that is too big or too small for your application, you’ll see a reduction in vehicle performance.
How Are Big Exhaust Pipes Bad Again?
Often times vehicle enthusiasts assume that bigger exhaust pipes are better, because bigger pipes would seem to be less restrictive. While this is perfectly logical thinking, it’s incorrect. Thinking only about exhaust pipe size overlooks the fact that exhaust gases are cooling as they travel.
If you have a 1″ single exhaust system, your exhaust gases are going to flow faster than if you have a 3″ exhaust pipe. As a result, they’re not going to have much of a chance to cool. Because the gases stay hot, they’re less dense and therefore easier to “push” out of the pipe. Of course, a 1″ exhaust pipe can also be restrictive, as it’s just not big enough to handle the volume of exhaust created by your vehicle’s engine (at least if your engine makes more than 50hp).
The “sweet spot” is an exhaust pipe diameter that’s big enough to handle your engine’s output, but not so big that exhaust gases can linger in your system and cool down. What’s the sweet spot for your engine? That’s the million dollar question, as it depends on how your vehicle is tuned, what after-market parts you may have installed, etc.
The point? Exhaust systems are a little more complex than they might seem. Therefore, when you buy an after-market cat-back system or muffler, be sure to buy parts that are designed for your vehicle….which brings me to TRD exhaust systems.
TRD exhaust systems are always designed for your application, so be sure to take a look at them.