High Flow Cat vs No Cat: A Head-to-head Comparison

Written by

Charles Bolte


Vernon Hoppe 

high flow cat vs no cat

If you’re looking for better performance in your vehicle, you may have heard about high flow cats vs no cats.

These two options are often compared to each other, while the former features a catalytic converter, the other comes without one. Both high-flow and no-cats can help improve engine performance, but which one is best for your needs?

In this article, we’ll look at the pros and cons of both set-ups and an in-depth comparison of their features so that you can make an informed decision.

What Are High-flow Catalytic and No-Catalytic?

1. High flow cat


If you’re looking to get the most out of your vehicle’s engine, then a high-flow cat – or catalytic converter – is the way to go. But what exactly is it?

High-flow cats are typically made of stainless steel or titanium, with more giant honeycomb cells than stock cats, allowing more exhaust gasses to pass through. In other words, it provides an increase in airflow and allows your car to reach its peak performance while also reducing back pressure on your engine.

When it comes to flow, high-flow cats outflow standard cats by about 20-30%.

2. No cat


On the other hand, no cats mean on a car, it provides the highest amount of gas flow as it has no metals or other substances that can function as a catalyst to lessen emissions, producing an adverse effect on the environment.

The no-catalytic converter is installed for initial engine performance. Beside not restricting the flow of your car’s exhaust gas, it is also lighter than a high-flow catalytic.

What Does a High Flow Cat Do?

A high flow cat is designed to balance emissions standards and increased power. Inside a high flow is its inner shell cat, which allows for improved gas flow and performance. Although it may cause some power loss due to back pressure, it can be mitigated with a proper tune-up.

High flow cats are designed to provide the best of both worlds, letting drivers maintain emissions compliance while enjoying some benefits of no cats.

How Does a No-cat Work?

On the other hand, your modern car engine can totally run with no catalytic converter without breaking down. In this case, the exhaust gases just flow through the converter freely.

What is the Difference?


1. Performance

High Flow Cats are designed to reduce back pressure at higher RPMs, which helps the engine generate more power with less strain.

On the other hand, no cats increase back pressure, which can affect engine performance.

2. Sound

Without a catalytic converter, your exhaust will be much louder, as the muffling effect from the cat is gone. The system’s sound will be deeper and more aggressive.

High flow cats can also produce a meaner growl than regular cats while still providing increased performance. However, they make less noise than those without a catalytic converter.

Pros and Cons of High Flow Cat

  • Increased power and provides a noticeable jump in performance.
  • Reduce backpressure, which can lead to better fuel economy.
  • Increase exhaust temperatures due to their larger opening size. This is why it’s vital to use catalytic converters designed for higher-temperature applications such as turbocharged engines or aftermarket headers.
  • High flow cats change sound as it will produce more than stock converters, so if noise reduction is your goal, you may want to stay away from this option.

Pros and Cons of No Cat

  • Increased performance: With the removal of the cat, more exhaust can flow from the engine, resulting in improved power output
  • Cheaper than buying a high flow catalyst: If you don’t have the money for a higher-flow catalyst, removing it may be your only alternative
  • Weight Reduction: Removing the catalytic converter can reduce vehicle weight by up to 20 pounds, resulting in improved fuel economy
  • Emissions increase significantly: As there is no further filtration of the exhaust gasses, harmful pollutants such as nitrogen oxide (NOx) are released into the atmosphere at much higher concentrations than with a catalytic converter installed
  • Illegal in many states/countries: Many countries have laws requiring all vehicles to use a catalytic converter – bypassing these laws is illegal and can lead to hefty fines or even car confiscation.

Cost: The Difference in Price

High-flow cats are much more expensive than their no-cat counterparts, as it can be over $300 – $380, about $60 higher than the price with no catalytic.

On the other hand, removing the factory cat altogether – also known as “gutting” – can save you upfront costs but may be a false economy over time. Removing the cat may make the exhaust louder and reduce engine performance.

But are high flow cats worth it? Shortly, yes! Why, you ask? The answer lies in the next section.

Which is Better?

When it comes to deciding between a high flow cat and a no cat system, people often prefer the former. Still, each option has its own advantages and disadvantages.

Ultimately the decision comes down to your individual needs and preferences. Going with no cats is your best option if you want the most power. However, if you prefer streetable performance gains, you should go with a high flow cat. Plus, if you’re looking to get the most out of your vehicle’s engine, a high flow catalytic converter– is the way to go.

Tips for Choosing the One for You


When deciding between a high flow cat and no cat, you’ll want to consider your driving style, local laws, and personal preference. Here are a few helpful tips to consider:

1. Driving Style:

If your driving style is mostly light cruising and occasional sprinting, then a high flow cat is the better choice.

High flow cats allow smoother transitions from the accelerator and offer better exhaust sound at higher RPMs, allowing for a more pleasurable driving experience.

2. Personal Preference

Ultimately, it’s up to you to decide whether a high flow cat or no cat is best for you based on how much power and sound you want out of your car.

If more power and louder sound are what you’re after, then going with a no-cat setup may be right up your alley.

On the other hand, if you want smoother acceleration with less ruckus coming out of your exhaust pipes, opting for a high-flow cat may be ideal for you.

Factors Affecting the Performance of High-flow Cat and No Cat


1. Environmental conditions

High-flow cats are particularly affected by environmental conditions such as temperature, humidity, and altitude. In cold or wet climates or higher altitudes, a high-flow cat will not perform as well as a no-cat.

On the other hand, in hot climates or at lower altitudes, a high-flow cat can outperform a no-cat.

2. Driving style

If you are the type who likes to drive fast and push your engine hard, then you might benefit from the increased airflow offered by a high-flow cat.

On the other hand, if you prefer gentle acceleration and cruising speeds, there is little difference in performance between a high-flow cat and a cat system.

The Connection Between the Exhaust System and the Engine

The debate between high-flow cats and no cats involves the exhaust system’s role in transferring heat generated from combustion.

Catless exhausts with numerous bends can cause turbulent airflow and back pressure, and restrict exhaust gas release, leading to reduced power and performance.

High-flow cats allow greater airflow while reducing emissions and maintaining vehicle performance and lower emissions.

Frequently Asked Questions or Helpful Tips


Overview of Catalytic Converter

A catalytic converter is an emissions control device that helps to minimize your vehicle’s emissions, and since it does not affect performance levels or require regular maintenance, it has become increasingly popular over the years.

Are high flow cats as loud as no cats?

High-flow cats may be slightly quieter than no cats but will offer improved performance benefits, making them worth considering for those who want improved performance and sound.

Will a high flow cat make my car faster?

While a high-flow cat can enhance overall engine performance, it won’t necessarily make your car faster.

In most cases, the difference in engine performance after installing a high-flow cat is minor, so if you’re looking for more power, you’ll probably need to look elsewhere.

Why Does My Dash Still Show an Error Code After Removing the Catalytic Converter?

If that’s the case, this is so that the converter may be monitored to make sure it is operating properly using the post-cat with O2 sensors. The sensors won’t work properly without the converter and will generate an error code.

If you own a Silverado Exhaust?

If you have a 2000 Silverado z71 cat-back exhaust, install the intake and headers at the same time that you switched the cats to increase your HP gain.

High-flow vs stock cat

You might also encounter a stock catalytic converter coming in a circular frame. It is a tad bigger than a high-flow cat, safer, and more efficient for regularly driven vehicles. It is considered the better choice for the life span of engine components.


In conclusion, it’s clear that high flow cats can bring performance gains, but these should be weighed against the current restrictions imposed on them in some areas.

For most drivers who just want to get the best out of their factory setup, no cats are the obvious way to go. However, high flow cats can offer a great way to enhance vehicle performance when looking for increased sound and power. Ultimately, the decision comes down to the individual and their needs.

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