What They Sold: A Hardware Catalog for Poisoning the Air

Thoroughbred Performance Products, Inc. — doing business as Thoroughbred Diesel out of Winchester, Kentucky — operated as a nationwide retailer of diesel performance parts. Between September 1, 2018, and October 10, 2019, the company made a documented 15,247 sales of hardware with one specific purpose: to strip federally-mandated pollution controls out of diesel trucks.

The EPA’s enforcement document lays out the three product categories in plain terms. First: 4,858 sales of Exhaust Gas Recirculation (EGR) delete hardware. Second: 10,079 sales of exhaust emission control delete hardware — products that physically remove diesel particulate filters, catalytic converters, and selective catalytic reduction systems. Third: 310 sales of tuning products — software packages that reprogram the truck’s computer to pretend the pollution controls are still there while the vehicle runs dirty.

The parts came from at least ten manufacturers: aFe, Deviant Race Parts, Diesel Site, Diamond Eye Performance, Flo-Pro, GDP, MBRP/P1 Race Parts, MagnaFlow, OZ Tuner, SC Supply, Silverline, Sinister Diesel, H&S Performance, and RaceME. They covered virtually every major diesel truck platform on American roads — Ford F250/350 Powerstroke, Dodge/RAM 2500/3500 Cummins, and Chevy/GMC Silverado/Sierra Duramax — spanning model years from 2001 through 2019.

The scale of this operation is impossible to brush off as a few garage sales. In just 13 months, Thoroughbred Diesel processed more than 1,172 defeat device transactions per month on average. These parts shipped to distributors and customers across the entire United States, meaning their pollution impact radiated outward from Winchester, Kentucky into every zip code in the country.

The Emissions Systems They Killed

To understand what these products actually do, you need to know what they destroy. A diesel truck leaves the factory with several interlocking emissions systems. The Exhaust Gas Recirculation (EGR) system loops exhaust back into the engine to reduce the formation of nitrogen oxides — compounds that cause smog and respiratory disease. The Diesel Particulate Filter (DPF) catches the fine black soot particles that diesel combustion produces, particles small enough to penetrate deep into human lung tissue. The Selective Catalytic Reduction (SCR) system injects a urea solution to neutralize nitrogen oxides before they exit the tailpipe. And the On-Board Diagnostic (OBD) system constantly monitors all of these — it is the truck’s own referee, catching cheating.

Thoroughbred Diesel sold hardware to disable every single one of these systems. The tuner products went further: they reprogrammed the engine control unit to pretend the deleted systems still existed, silencing any warning lights and making the vehicle appear compliant during standard inspection procedures. This is not a performance upgrade. It is engineering a lie into the machine.

The Non-Financial Ledger: What Money Can’t Measure

When regulators close a case like this, the story they tell is built around numbers: violations committed, dollars paid, days to comply. What gets left out of that ledger is the experience of living downwind. Diesel exhaust particulate matter — the specific pollution that Thoroughbred Diesel’s products unleashed in greater quantities — is classified by the World Health Organization as a Group 1 carcinogen, the highest category of confirmed human cancer risk. Every one of those 15,247 transactions represents a truck that drove through someone’s neighborhood, idled outside someone’s school, sat in traffic beside someone’s car window, and pumped out a heavier load of toxins than the law permits. No dollar figure appears next to those moments in the settlement document.

The defeat device market overwhelmingly serves the working-class truck owner: tradespeople, contractors, farmers, and small fleet operators who bought into promises that deleting their emissions system would save them money on maintenance and improve fuel economy. Many of these buyers trusted that the products were legal, or at minimum did not understand the full implications of what they were installing. The EPA’s legal standard is clear: Thoroughbred Diesel “knew or should have known” these products were being used to defeat emissions compliance. The company carried that knowledge. Many customers did not. The betrayal here runs in multiple directions simultaneously — the company betrayed its customers, and through its customers, it betrayed every community those modified trucks drove through.

There is also the question of what happens to air quality enforcement at the neighborhood level when an operation like this runs for over a year without interruption. The EPA sent its information request on October 10, 2019 — meaning the agency had gathered enough intelligence to make a formal inquiry, but Thoroughbred Diesel had already completed the bulk of its illegal sales run. By the time a Notice of Potential Violation was issued on July 21, 2021 — nearly two years after the investigation opened — those trucks were already on the road. Negotiations between the EPA and Thoroughbred Diesel stretched across eight separate meetings over more than two years, from August 2021 to January 2024. The trucks were already polluting. The talks were largely about price.

The consent agreement’s most quietly damning passage acknowledges that Thoroughbred Diesel’s penalty was “compromised” — reduced from what it could have been — based on a “substantiated ability to pay claim.” In plain English: the company told the EPA it could not afford the full fine, and the EPA agreed to take less. The resulting $1,250,000 ($1.25 million — roughly equivalent to what a median-wage American worker earns across 30 years of full-time employment) is presented in the document as a victory for enforcement. The communities whose air was dirtied by 15,247 defeat device sales did not get a seat at that negotiating table, and no portion of that fine goes to them.

The Price They Put on a Violation

To put the $1,250,000 (enough to pay the annual salary of about 21 public school teachers at median US pay) in full context: the Clean Air Act authorizes penalties up to several thousand dollars per violation. At the maximum statutory rate, 15,247 violations could have generated a fine in the tens of millions of dollars. The EPA and the Department of Justice jointly agreed to reduce this to $1.25 million based on Thoroughbred Diesel’s ability-to-pay argument. The company was not fined for the harm it caused. It was fined for what its accountant said it could afford.

Legal Receipts: Straight From the Government’s Mouth

These are verbatim passages from the EPA’s own Consent Agreement and Final Order. Read them in the voice of a government that found a company breaking the law 15,247 times and then agreed to a quiet settlement.

“Based on the information provided in the Respondent’s response to the Request, on at least 15,247 occasions between September 1, 2018, and October 10, 2019, Respondent sold and/or offered to sell defeat devices identified in Appendix A of this CAFO. These sales included 4,858 sales of the exhaust gas recirculation delete hardware products identified in Appendix A, 10,079 sales of the exhaust emission control delete hardware products identified in Appendix A, and 310 sales of the tuning products identified in Appendix A.” — EPA Consent Agreement and Final Order, Section V: Alleged Violations, Paragraph 29

“The aftermarket defeat devices were designed and marketed for use on various motor vehicles, and intended to bypass, defeat, or render inoperative emissions-related devices or elements of design such as the exhaust gas recirculation, catalytic converters, diesel particulate filters, selective catalytic reduction, and on-board diagnostic systems that are installed on those motor vehicles to meet the CAA emission standards.” — EPA Consent Agreement and Final Order, Section IV: Findings of Facts, Paragraph 23

“Respondent consents to the payment of a compromised civil penalty with conditions, which was calculated in accordance with the Act and based on the Respondent’s substantiated ability to pay claim, in the amount of $1,250,000, which is to be paid within thirty (30) calendar days of the Effective Date of this CAFO.” — EPA Consent Agreement and Final Order, Section VII: Terms of Payment, Paragraph 37

“For the purpose of this proceeding, as required by 40 C.F.R. § 22.18(b)(2), Respondent: neither admits nor denies the factual allegations set forth in Section IV (Findings of Facts) of this CAFO; consents to the assessment of a civil penalty as stated below; waives any right to contest the allegations set forth in Section V (Alleged Violations) of this CAFO; and waives its rights to appeal the Final Order accompanying this CAFO.” — EPA Consent Agreement and Final Order, Section VI: Stipulations, Paragraph 34

“Respondent knew or should have known that the aftermarket defeat devices identified in Appendix A were being offered for sale for such use or put to such use, in violation of Section 203(a)(3)(B) of the Act, 42 U.S.C. § 7522(a)(3)(B).” — EPA Consent Agreement and Final Order, Section V: Alleged Violations, Paragraph 31

Societal Impact Mapping

Public Health: The Exhaust You Didn’t Consent To

Diesel particulate matter is among the most dangerous forms of air pollution in terms of documented human health outcomes. The emissions systems that Thoroughbred Diesel’s hardware destroyed — diesel particulate filters, catalytic converters, and selective catalytic reduction systems — exist specifically to reduce emissions of nitrogen oxides, soot particulates, and hydrocarbons from diesel combustion. Without these systems, a modified truck emits these pollutants at levels that pre-date modern emissions standards, effectively rolling back the clock on air quality by decades for anyone in the exhaust path.

The EPA document identifies several specific systems rendered inoperative by Thoroughbred Diesel’s products: exhaust gas recirculation, catalytic converters, diesel particulate filters, selective catalytic reduction, and on-board diagnostic systems. Each of these controls a different class of harmful emission. EGR reduces nitrogen oxides, which react with sunlight to create ground-level ozone and fine particulate smog. DPFs capture soot particles in the PM2.5 range — particles under 2.5 microns in diameter — that penetrate deep into lung tissue and cross into the bloodstream. SCR systems reduce the final nitrogen oxide concentration before exhaust exits the tailpipe. Thoroughbred Diesel sold the tools to disable all of them, 15,247 times, on trucks that then drove on public roads shared by children, elderly people, and anyone else unfortunate enough to share the road.

The 310 tuner products in the catalog carry a particularly insidious public health dimension: they disable the on-board diagnostic system, the mechanism that would otherwise trigger a check engine light and flag the truck as non-compliant during emissions inspections. A truck running with a deleted DPF and a tuner that masks the deletion will pass a visual inspection in states that conduct them, and will throw no codes detectable at a smog check. The product was not just a pollution bypass; it was a bypass for getting caught bypassing pollution.

Environmental Degradation: Regulatory Rollback, One Delete at a Time

The Clean Air Act’s vehicle emissions standards represent decades of scientific consensus, legislative action, and regulatory rulemaking designed to reduce the cumulative air quality burden on American communities. Every defeat device sale undermines that infrastructure directly. The EPA’s own governing law section in this document states that emissions standards are required for pollutants that “may reasonably be anticipated to endanger public health or welfare.” Thoroughbred Diesel sold hardware specifically engineered to override those standards on 15,247 occasions.

The product list in Appendix A covers trucks manufactured from model year 2001 through 2019 — an 18-year span of vehicle production. This means some of these products targeted trucks already subject to more than a decade of stricter emissions standards. The Duramax, Cummins, and Powerstroke engines covered in the catalog are workhorses found on construction sites, farms, and delivery routes — high-mileage, high-idling environments where emissions controls matter most. Removing a DPF from a truck that logs 80,000 miles a year multiplies the pollution output exponentially compared to a passenger sedan. The environmental mathematics here are brutal: 10,079 DPF and exhaust system delete sales on high-mileage commercial vehicles represents a cumulative pollution load that dwarfs what the fine acknowledges.

Economic Inequality: Who Pays For Cheap Compliance

Thoroughbred Diesel’s customer base — diesel truck owners dealing with expensive DPF regeneration cycles, EGR cooler failures, and DEF fluid costs — represents exactly the class of person who gets squeezed hardest when corporations externalize costs. The diesel emissions control systems that Thoroughbred Diesel’s products bypass are not cheap to maintain. DPF replacements can run into the thousands of dollars. EGR cooler failures are notorious on the 6.0L Ford Powerstroke platform specifically targeted by multiple products in the catalog. The company marketed an escape hatch for working people trapped between expensive repairs and equipment they couldn’t afford to replace — and in doing so, turned those working people into unwitting pollution generators.

Meanwhile, the communities that bear the highest air quality burden from diesel pollution are disproportionately low-income. Research on environmental justice consistently finds that truck routes, distribution hubs, and high-diesel-traffic corridors run through lower-income neighborhoods. The externalized cost of 15,247 illegal defeat device sales is not distributed equally. The fine of $1,250,000 (roughly enough to fund clean air monitoring equipment for several mid-sized cities for a year) goes to the federal treasury. The communities breathing the pollution got nothing.

There is also a structural economic harm in the defeat device market itself. Legitimate diesel repair shops and dealerships that maintain emissions systems in compliance with the law compete in a market distorted by businesses selling illegal bypasses. When a competitor can offer a customer “skip the $2,500 DPF replacement, just delete it for $300,” compliant businesses lose customers. The enforcement action against Thoroughbred Diesel represents one acknowledged node in a nationwide defeat device market that the EPA has been pursuing through multiple simultaneous cases. The structural damage to fair competition is real and ongoing.

What Now? Who to Watch and What to Do

The People at the Center

• M. Dennis Craig — Owner, Thoroughbred Performance Products, Inc. d/b/a Thoroughbred Diesel. Named in the certificate of service as the corporate owner. The settlement binds him, his company, its successors, and assigns.
• Thoroughbred Performance Products, Inc. — Located at 4843 Rockwell Road, Winchester, Kentucky 40391. The settlement agreement binds any future buyer or successor of the business to the same compliance obligations.

The consent agreement that I pulled to write this article came from this following link from the EPA’s website: https://yosemite.epa.gov/OA/RHC/EPAAdmin.nsf/Filings/E7C567DF389B3A3C85258B030079167C/$File/THOROU~4.PDF

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