Removing a catalytic converter produces little to no performance gain on most vehicles. On a naturally aspirated engine, you can expect roughly 5 to 15 horsepower at best, which is barely noticeable during everyday driving. The idea that catalytic converters are a major bottleneck for engine power is one of the most persistent misconceptions in car culture, and dyno testing consistently shows the gains are minimal.
Why People Think It Works
The theory behind a catalytic converter delete sounds logical on the surface. Your engine pushes exhaust gases out through the exhaust system, and anything in the path creates resistance, known as backpressure. A catalytic converter is a honeycomb structure that forces exhaust through thousands of tiny channels, which does restrict flow to some degree. Remove that restriction, and exhaust exits more freely.
When backpressure is genuinely high, it causes real problems. Exhaust gas gets stuck in the cylinder at the end of the exhaust stroke, taking up volume where fresh air should enter on the next intake cycle. The next combustion event loses power because there’s less oxygen available to burn fuel. Reducing that backpressure lets the engine breathe better and produce more complete combustion cycles. In theory, removing the cat should help. In practice, the restriction from a modern catalytic converter is small enough that eliminating it barely moves the needle.
What Dyno Tests Actually Show
Real-world dyno results tell a consistent story. A Honda Element owner who removed the catalytic converter and tested on a dyno measured about 5 horsepower gained over a previous baseline of 147 horsepower. That’s roughly a 3% increase, which you would struggle to feel from the driver’s seat.
On the higher end of the spectrum, Hot Rod magazine tested a high-horsepower V8 setup with and without catalytic converters. Running straight pipes (no cats at all) produced 660 rear-wheel horsepower, a gain of just 9 horsepower over the baseline with stock catalysts. On a 660-horsepower engine, that’s about a 1.4% difference. The exhaust pressure ahead of the catalytic converters measured only 2.3 psi above atmospheric pressure, just 1.5 psi more than running open pipes. That tiny pressure difference explains why the power gains are so small.
Turbocharged engines sometimes see slightly larger gains because the turbo is already working against exhaust restriction, so any reduction in backpressure helps the turbo spool more efficiently. But even then, the improvement from removing the cat alone is modest compared to other modifications like a proper tune, upgraded intake, or larger turbo.
High-Flow Catalytic Converters Close the Gap
If a stock catalytic converter creates a small restriction, a high-flow aftermarket catalyst creates almost none. These units use a less dense honeycomb structure with larger cells, allowing exhaust to pass through with minimal resistance while still processing emissions.
Hot Rod’s testing demonstrated this clearly. Their high-flow catalytic converters produced the same 660 rear-wheel horsepower as running no catalytic converters at all. Zero difference. The pressure readings confirmed it: the high-flow cats added almost no measurable backpressure beyond what open pipes created. So the performance argument for a full delete largely disappears when a high-flow option exists.
Effects on Fuel Economy
Some owners report modest fuel economy improvements after removing catalytic converters, typically in the range of 2 to 3 mpg. Others notice no change at all. The logic is the same as with horsepower: less exhaust restriction means the engine doesn’t have to work as hard to push gases out, so it can operate slightly more efficiently.
However, these gains depend heavily on how the engine’s computer responds to the change. Modern vehicles use oxygen sensors downstream of the catalytic converter to monitor its function. Removing the cat triggers a check engine light and can cause the engine management system to adjust fuel delivery in ways that offset any efficiency gain. Some owners work around this by reprogramming the engine computer or installing sensor simulators, but at that point you’re stacking modifications and moving further from a simple bolt-off improvement.
The Check Engine Light Problem
Nearly every vehicle made after 1996 has a second oxygen sensor behind the catalytic converter. Its sole job is confirming the cat is functioning. Remove the converter and this sensor sends readings that trigger a check engine light, typically a P0420 or P0430 code. The light itself is more than cosmetic. While the engine will still run, having a persistent check engine light means you won’t know when something else goes wrong, because the warning system is already tripped. You also won’t pass emissions inspections in states that require them.
Clearing the code with a scanner is temporary. It comes back within a few drive cycles. The only lasting fixes are an engine tune that disables the rear oxygen sensor monitoring, or a physical spacer that moves the sensor out of the direct exhaust stream. Both add cost and complexity to what’s supposed to be a simple performance modification.
Legal Consequences Are Serious
Removing a catalytic converter from any vehicle driven on public roads violates the federal Clean Air Act. This applies in all 50 states, regardless of whether your state has emissions testing. The EPA treats catalytic converter removal as tampering with an emissions control device, and the penalties are steep. Civil fines can reach $4,527 per tampering event for individuals and up to $45,268 per noncompliant vehicle for commercial operations. Shops that perform the work face the same penalties, and the EPA has increasingly pursued enforcement actions against both businesses and aftermarket parts sellers.
State-level consequences vary. In states with regular emissions inspections, a missing catalytic converter means automatic failure. In California, the penalties are particularly aggressive, with fines and mandatory restoration of the emissions equipment. Even in states without inspections, your vehicle is still federally noncompliant, which can become an issue during resale, insurance claims, or if you’re ever pulled over for an exhaust noise complaint.
What Actually Improves Performance
If you’re looking for noticeable power gains, the catalytic converter is one of the least effective places to start. A proper engine tune on a stock turbocharged car can unlock 30 to 80 horsepower depending on the platform. A cold air intake and tune together often outperform a cat delete by a wide margin. For naturally aspirated engines, headers, a freer-flowing exhaust (with a high-flow cat still in place), and a tune will produce results you can actually feel.
The exhaust system as a whole matters more than any single component. Properly designed systems use exhaust pulse scavenging, where the pressure waves from one cylinder help pull spent gases from another, improving flow without simply making the pipe bigger or removing components. A well-engineered cat-back exhaust system with correct pipe diameter and a high-flow catalytic converter will get you within a few horsepower of a straight pipe setup while keeping your vehicle legal, your check engine light off, and your neighbors tolerant of your exhaust note.