Updated: Jan 9
A straight pipe is an exhaust system which has no restrictive components or parts, this is usually done by removing parts like the catalytic converter, mufflers, and particulate filters.
In this article, we discuss the straight pipe exhaust, advantages and disadvantages, as well as if it's legal or not.
Table of Contents:
What Is a Straight Pipe Exhaust?
A straight pipe is a term for an exhaust system without any components interrupting the flow of exhaust gas, this includes emissions control and sound reducing components. This is why it has the name "straight pipe", exhaust gases go straight out.
Straight pipe exhausts typically remove the components listed below, some vehicles will have some or all these components as standard.
Particulate filters (GPF, DPF, etc)
Mufflers / silencers
A manufacturer must ensure a vehicles exhaust system meets a number of regulations. Car manufacturers, particularly those in Europe, add particle filters, sound reducing components (mufflers / silencers), and catalytic converters to comply with these regulations.
These parts may reduce the flow of exhaust gas, creating back pressure in the exhaust system and reducing engine efficiency.
Does a Straight Pipe Increase Power?
Installing a straight pipe exhaust to your vehicle can increase power and torque by about 5-10% providing the cars ECU is programmed to make use of the improved exhaust flow.
Straight piping your vehicle will reduce restrictions in the exhaust system, improving exhaust gas flow and therefore reducing back pressure.
Reduced back pressure can improve engine efficiency and power by:
Improving exhaust scavenging
Reducing pumping losses
Allowing for increased boost pressures
Can It Harm Your Engine?
A straight pipe exhaust should not cause harm or damage to an engine. Although emissions control and sound reducing components are needed to meet the legal requirements, they're not essential for a vehicle to function.
If these parts are removed, providing the exhaust sensors (oxygen sensor, exhaust gas temperature sensor, etc) are still in place, no harm should occur.
Is Straight Piping Your Car Legal?
Legality of exhaust modifications and exhaust sound limits differ depending on the country, generally the following statements are true.
If an exhaust system causes the vehicle to fail emissions testing its usually illegal.
If an exhaust system causes excessive sound (over the legal exhaust decibel limit) its usually illegal.
Because a straight pipe exhaust removes all sound and emissions reducing components, its most likely not legal. Some insurers won't cover illegal modifications such as a straight pipe or a decat, making them not road legal.
The laws surrounding exhaust modifications vary by country. In many developed countries such as the United States, United Kingdom, Canada, and Australia, modifications to the exhaust system are highly regulated or even prohibited.
Always check your local laws regarding a straight pipe exhaust.
You should be aware that most racing tracks and courses have decibel limits, which means that straight piping your vehicle may restrict you from driving on a race track.
There are some clear advantages to a straight pipe exhaust system, such as the following.
Less expensive. Because the emissions control and sound reducing parts of an exhaust are expensive, removing them makes for an inexpensive exhaust system.
Increased power and torque. Removing restrictions from the exhaust system will reduce back pressure and improve exhaust gas flow, allowing for extra power potential.
Improved efficiency. There may be a marginally improved fuel efficiency of a straight pipe vehicle, this is due to reduced back pressure, improving engine scavenging and reducing pumping loss.
Reduced weight. Due to removing emissions and sound reducing parts the exhaust system will be lighter and reduce the overall weight of the vehicle.
Although there are some advantages to a straight pipe exhaust, there are also some serious disadvantages.
Increased noise. Some people like increased exhaust noise, other people don't. A straight pipe exhaust removes all sound reducing components and is as loud as an exhaust can get (though a screamer pipe could be louder).
Cabin drone. A straight piped exhaust system will produce strong vibrations and allow harsh sound waves from the exhaust to pass through the vehicle into the cabin, producing a "drone" inside the car, even while driving normally.
Increased emissions. A straight pipe usually removes all emissions control components, such as particulate filters and catalytic converters. This will cause the vehicle to fail emissions testing in most circumstances.
Illegal in most countries. Since most countries have an exhaust sound decibel limit and emissions testing, straight piping a car would make it illegal on the road.
May not get insured. Some car insurers won't insure a car with illegal modifications, this includes a straight pipe and decat exhaust.
Restricted from racing tracks. Most racing tracks and courses have an exhaust decibel limit, removing the sound reducing parts like mufflers and resonators will likely prevent you from driving on a race track.
Should You Straight Pipe Your Car?
In almost every situation it doesn't make sense to straight pipe your car, it will likely fail emissions and exhaust sound testing, making it illegal on the road. You will also be restricted from driving on most race tracks due its excessive loudness.
The power and efficiency increase does not make up for the disadvantages of this type of exhaust system.
Some insurance providers will also not provide cover if your vehicle has illegal modifications, such as a decat or straight pipe.