How Emissions Regulations Affect Diesel Performance Mods

One of the biggest draws of diesel engines is their longevity. A well-maintained diesel engine lasts for decades, and those passionate about their machines' regular upkeep, care, and modifications still have these legacy vehicles on the road today. So, what's the history of emission regulations, and what effect have they had on diesel performance modifications? Today, we’re looking back at the history of clean air bills, the environmental protection agency, and the modern revolution of diesel engines.

Where Engine Regulations Began

Early attempts at regulating the output from diesel engines start as far back as the 1960s. In 1963, President Lyndon Johnson passed the Clean Air Act. This was the first federal law to introduce regulations focusing on improving air quality and reducing emissions.

The Clean Air Act, expanded in 1970 by President Richard Nixon, created new limits on emissions and brought focus to those produced by motor vehicles instead of the previous guide, mainly holding power plants and industrial buildings accountable. The year 1970 also marked the creation of the Environmental Protection Agency (EPA) and appointed William Ruckelshaus as its first administrator.

The Environmental Protection Agency introduced new amendments to the Clean Air Act throughout the years, with more extensive, stricter overhauls to the law coming between the 1980s and the early 2000s. Emissions regulations introduced in 2002 put pressure on engine manufacturers to comply with the new systems and create machines with fewer toxic outputs.

Diesel Emissions Reduction Act

A significant turning point for diesel engines, specifically, came about as part of the Energy Policy Act of 2005. This act allows the federal government to award grants, funding, and aid to manufacturers to re-build, re-tool, or modify their diesel engines to comply with modern Environmental Protection Agency standards.

An interesting facet of the diesel emissions reduction act is that while many states had the go-ahead to set their own standards for proper regulations, California enacted the strictest policies through the California Air Resources Board (CARB). This put pressure on manufacturers to comply with California policy, regardless of what other states allow. Many found that it didn't do much good to pass emission regulations in 49 states if it meant paying fees or missing out on possible grant money through a California inspection.

The Diesel Emissions Reduction Act continued receiving funding and upgrades. In 2020, the program got additional funding of up to $100 million throughout 2024. DERA has replaced and upgraded the diesel engines in over 300 school buses annually since 2019 and reduced emissions in over 70,000 engines.

Why Regulate Diesel Emissions?

The Clean Air Act eventually put pressure on engine manufacturers and other industrial offices, but what were the specific reasons for these crackdowns? What was the basis for the Environmental Protection Agency’s strict guidelines?

Exposure to diesel emissions can result in respiratory illnesses, frequently among children and the elderly, and increase the likelihood of negative symptoms from heart and lung conditions. Older diesel emissions also created ground-level ozone, negatively affecting crops, soil, and water supplies.

The Diesel Emission Reduction Act existed to attempt to lower these harmful emissions and encourage engine manufacturers to lower their harmful outputs and focus on new engine options. However, that wasn’t the smoothest transition for most companies on the market.

Early Emission Regulation Modifications

Perhaps the strictest regulation on diesel engine manufacturers from the Environmental Protection Agency was in 2007 when the EPA declared that every single engine used in heavy-duty vehicles on the highway must comply with the current emission compliance standards of the Clean Air Act. The 2007 standards included 50% reductions in nitrogen oxides and a 90% reduction in particular matter emissions compared to only a few years ago.

These strict guidelines put immense pressure on production companies, and many scrambled to work with the new limitations to create diesel engines that adhere to the current standards without sacrificing quality or power.

In the early days of these new systems, many customers were uncertain or unhappy with the changes in place. There was noticeable damage to the fuel economy, parts for older systems were scarce, and the original equipment manufacturers faced barrages of complaints as these OEMs rolled out more and more updates attempting to comply with the EPA regulations.

On the flip side, early adopters of the new systems found them mostly reliable. Like a proper diesel engine, it takes time to warm up before things start running at their most optimal.

Manufacturer Solutions

Most manufacturers of diesel auto parts shifted focus onto exhaust gas recirculation systems (EGRs) that controlled emissions and significantly reduced the amount of NOx from diesel engines. By focusing on the EGR cooler and EGR valve, the new systems cooled gas to make it more compatible with combustion and created cleaner power with fewer emissions.

However, as one of the leading figures in the diesel market, Caterpillar had their own solutions for complying with regulations on the horizon. Cat introduced the ACERT (Advanced Combustion Emissions Reduction Technology) system.

Compared to Cat’s C15 engine from the 1990s and the C15 ACERT from 2004, Cat made a few modifications to make their new system better for the environment and more likely to pass the harsher standards set on federal and state levels. The C15 ACERT includes a second turbocharger and an improved single-piece piston design. In the early days, Cat encountered issues with rocker studs breaking. Still, consumer feedback resulted in modifications, and the C15 ACERT remains a robust and reliable engine that Cat sells to this very day.

Where We Are Now

In the late 2000s, the thoughts regarding how emission regulations would affect diesel performance modifications were a legitimate concern. Many older engines were phased out for new systems that brought their issues to the table. It was a rough and concerning time for consumers and manufacturers. However, most manufacturers have cracked the code, and most performance engines on the market are running cleaner and more efficiently than ever before. The incredible adaptability and performance of the diesel industry remain a sight to behold. It's comforting to know that no matter what the future holds, strong-willed titans of the industry will continue to produce high-quality engines that live up to the expectations and emission regulations without sacrificing the ingenuity and performance that we expect.

For more information on emission-compliant diesel engines, ATL Diesel has what you need. Contact us today with any comments, questions, or concerns. You can reach ATL Diesel by phone at 1-866-905-3916 or email us at

How Emissions Regulations Affect Diesel Performance Mods