If you want to improve both horsepower and sound, then playing around with the exhaust system is your best bet. But there are so many options for exhaust systems – which one should you go for? In this article I want to discuss straight piping and cat-back exhaust. What are their differences and which one should you go for.
In most cases, you should go for cat-back exhaust instead of straight piping. Cat-back exhaust is legal and it improves both horsepower and sound – this is suitable for daily drivers or people who regularly drive on the street.
Straight piping makes you fail the emission test and it makes your car ridiculously loud – this is suitable for cars who absolutely need the horsepower and are driven on track.
With that being said, let’s go into details on both and see why I said what I said. 🙂
Recap: How Do Car Engines Generate Power?
Before we jump into how straight piping and cat-back exhaust can boost horsepower, we must first understand how car engines generate power.
Cars deliver power by generating combustion in the combustion chamber. Combustion is a controlled explosion that’s produced by igniting fuel injected into the combustion chamber.
From what science tells us, combustion uses up oxygen to exist. This is why your car constantly sucks air from the outside and delivers it to the combustion chamber – the more oxygen in the chamber, the bigger the combustion could be.
To boost horsepower, extra oxygen and fuel are needed in the combustion chamber. Injecting extra fuel is not a problem, getting the extra oxygen is. Every performance modification aims to somehow increase the amount of oxygen in the combustion chamber. Examples: aftermarket exhausts, turbos, nitrous, etc.
Recap: What’s Straight Piping?
Fun fact: straight piping has nothing to do with it being straight. Instead, straight piping means removing the catalytic converter (CAT), resonator and muffler from your exhaust system. This means your exhaust system is only made of a straight metal pipe – thus ‘straight piping’.
The idea of straight piping is that by removing the above components from the exhaust system, we remove unnecessary restrictions and allow exhaust gases to flow with ease and exit the car quickly.
How does this relate to horsepower? You see, when a combustion is generated, exhaust gases are produced. These exhaust gases are toxic and they occupy the combustion chamber. The exhaust gases must exit quickly – to provide space for new oxygen to enter for the next combustion cycle.
The faster the gases can leave the chamber, the more new oxygen can enter. Which means we can generate a bigger combustion for more horsepower.
As a side effect, cars with straight piping will be highly pollutant and noisy. This is because the CAT which cleans the exhaust gases is removed. And so is the muffler and resonator. If you don’t already know, mufflers and resonators significantly reduce the noise coming from an engine.
Straight piping is suitable for racers who absolutely need the extra horsepower and are only driving on track.
Recap: What’s Cat-back Exhaust?
Cat-back exhaust means replacing your exhaust system from the catalytic converter (CAT) and back. Cat-back exhaust does not replace the CAT. Instead, it replaces the metal piping beginning after the CAT, muffler and tail pipe.
The idea of cat-back exhaust is similar to the straight piping – where it aims to reduce restrictions for exhaust gases to flow out quickly.
Instead of removing components like straight piping, cat-back exhaust replaces them with less restrictive ones. This means cat-back exhaust will remove your stock exhaust components with below:
- Less restrictive muffler. Will not cancel sound as much, to allow exhaust gases to flow out more easily. As a side effect, your car engine will sound louder and more aggressive.
- Less restrictive piping. Will have a bigger diameter piping. This decreases the pressure in exhaust piping – allowing exhaust gases to flow with ease.
- Resonator exhaust pipe. This does not help with exhaust flow. Instead, it modifies the engine sound to be louder and more aggressive. Plus it looks more stylish.
In Cat-back exhaust, the catalytic converter and muffler are still attached. Which means your car will not be highly pollutant and not as noisy to the point it’s deafening. Very suitable for people who are operating on their daily drivers.
Straight Pipe Vs Catback
Now that we know the basics of the two, let’s compare them in more detail. 🙂
Summary: Both improves the car sound significantly but sound after straight piping could be deafening and illegal in states like California.
Straight piping removes the muffler and resonator from the exhaust system. Which means the sound from combustion is not suppressed at all. This produces engine sound that’s extremely loud and aggressive. Also, the law in strict states like California states that a car needs to have a working muffler at all time – making straight piping illegal in those states.
Cat-back exhaust replaces your stock muffler with one that’s less restrictive. This means the sound from combustion will still be suppressed, but not so much – resulting in a more aggressive and louder sound. When purchasing a cat-back exhaust, you could pick one which produces the sound you like and ensure it’s legal in your state.
Here’s a YouTube video showcasing the engine sound from a straight piped exhaust. Jump to 0:54.
Here’s another YouTube video showcasing engine sound from cat-back exhaust. Jump to 0:43.
2. Performance Gain
Summary: If tuned correctly, performance gain from straight piping is more than a cat-back. However, if left un-tuned, both straight piping and cat-back will not add much.
Winner: Straight piping
Straight piping has the advantage when it comes to potential horsepower gain. By removing all the components from an exhaust system, straight piping essentially allows exhaust gases to flow freely. However, you need to tune your car to take advantage of this. Otherwise, the horsepower gain is not significant.
Cat-back exhaust attempts to reduce restriction by replacing the stock components with aftermarket ones. This may work, but getting rid of the components altogether will definitely yield more results.
Summary: Price depends on what brand you choose – reputable brands are more expensive but more relatable. That being said, generally a set of straight pipes costs the same as a cat-back exhaust. However DIY straight piping is definitely cheaper than cat-back.
Winner: Straight Piping (DIY)
Straight piping requires you to purchase exhaust piping for the entire exhaust system. Depending on the material and brand, this could get expensive. However, you could create DIY straight pipes that are cheaper. The idea is to remove the CAT and muffler yourself and then weld an exhaust pipe extension in its place.
Cat-back exhaust requires you to replace the exhaust system after the catalytic converter. This usually involves cutting and welding a section from the exhaust system.
Summary: Cat-back exhaust is easier to install because you just have to weld it on your existing exhaust system. Straight piping requires you to replace the entire exhaust system. DIY straight piping can become even more complicated because you need to cut and weld multiple sections on your exhaust system.
Winner: Cat-back exhaust
Summary: Cat-back exhaust will not impact your car’s emission. As long as you don’t damage the existing CAT, then you are good to go. Straight piping removes the existing CAT – which will definitely cause you to fail the emission test.
Winner: Cat-back exhaust
6. Are They Legal?
Summary: When speaking of legal or not legal, engine sound is usually the biggest indicator. The law in strict states like California suggests that engine sound can only go up to 95 dBA. You could get a cat-back exhaust that produces engine sound below this level.
On the other hand, straight piping will never be legal because of the high emission and the fact that it does not have a working muffler.
Here’s a list of laws from different states regarding exhaust noise.
Winner: Cat-back exhaust
7. Will They Void Warranty?
Summary: With laws like Magnuson-Woss Warranty Act, dealers must prove that the problem is caused directly by your aftermarket installation. Otherwise, your warranty is still valid.
Which means you should not void your car warranty by doing any of both. That being said, straight piping is a much bigger upgrade with more things that could go wrong.
I have a post about muffler delete warranty where I discuss Magnuson-Woss Warranty act in more detail. Head over to the article here if you want to know more.
Winner: Cat-back exhaust
9 times out of 10 I would recommend going for a cat-back instead of straight piping. Straight piping is only suitable for a specific use case and that is racing on the track. Other than that, I don’t see any reason for anyone to straight pipe their cars – especially if it’s a daily.
Sound is deafening – inside and outside the car. Emission is extremely horrible and it’s outright illegal. All for the cost of horsepower boost – which is not even much by the way. Maybe 30-50 horsepower if you are lucky and you have tuned it. Not so great huh?
Cat-back exhaust on the other hand provides a great sound, great look and minor horsepower boost (if any). If you have a stock car and all you want is horsepower boost, then aftermarket exhaust is not the mod for you.
You should only rely on aftermarket exhaust for horsepower boost if you have installed all the other performance mods like turbos and exhaust headers. Simply installing an aftermarket exhaust, be it cat-back or straight piping will not improve horsepower by much.
If you have understood that, then I recommend you look into the Flowmaster exhaust system. Flowmaster is a reputable brand when it comes to exhaust systems and they have been around for some time.
I have an article here describing what to look for when purchasing an aftermarket exhaust system and why I go for the Flowmaster exhaust.