Motor Vehicle Gasoline Engine and Engine Parts Manufacturing (U.S.) — NAICS 33631

An investor's primer for public-market and private investors

Scope note: NAICS (North American Industry Classification System) code 33631 is a five-digit industry that contains exactly one six-digit national industry, 336310. Because there is only one child, this level is effectively identical to it. This page is a short rollup: it gives the level's own federal statistics and orients you, then points you to the full 336310 primer for the detailed treatment of companies, economics, regulation, and outlook.

1. Overview

This industry makes the gasoline engines that power most American cars and light trucks, and the precision parts inside them — pistons, piston rings, valves, turbochargers, fuel-injection systems, timing chains, and the castings and machined components that go with them. It is a foundational tier of the auto supply chain: when a U.S.-built vehicle rolls off the line with an internal-combustion engine (ICE — an engine that burns fuel in cylinders rather than running on a battery), the engine and its guts were classified here.

Why an investor cares: this is a large, cash-generative manufacturing base — roughly $39 billion in annual shipments [1] — that sits at the center of a slow, contested transition away from gasoline power. Electric vehicles (EVs) erode the long-run market for gasoline engines, but that shift has decelerated, hybrids (which still use a gasoline engine) are gaining, and the roughly 289 million vehicles already on U.S. roads [2] guarantee decades of replacement-parts demand.

Two things have changed since this page was last written, and both come from the child primer's newer sourcing. First, the industry is shrinking in headcount even as its revenue base holds: payroll employment fell from 61,615 in 2023 to 52,700 in May 2026. Second, the federal regulatory pressure that framed the old bear case has been withdrawn — the Environmental Protection Agency (EPA) rescinded its vehicle greenhouse-gas standards in February 2026. Both are treated below and in detail in the 336310 primer.

2. What's inside — and why this level equals its one child

At the five-digit level, NAICS 33631 has a single six-digit child:

When a NAICS industry has just one national industry beneath it, the two are definitionally the same set of establishments: the U.S. Census Bureau simply did not need to subdivide 33631 further. Every statistic, company, and dynamic that applies to 336310 applies to 33631 unchanged. There is no "rest of 33631" outside 336310 to add.

Where the boundary matters is what sits next to this code rather than inside it: diesel and stationary engines fall in NAICS 333618, transmissions and drivetrain equipment in 336350, electrical engine equipment in 336320, and final vehicle assembly in 336111/336112 [4]. That last exclusion is why Cummins and Caterpillar are adjacent rather than core names here, and why the automakers' own engine output is only partly visible at this level.

The industry's three kinds of players (detailed in the 336310 primer) are: (1) the automakers' captive engine plants — GM, Ford, Stellantis, Toyota, Honda — which are the highest-volume U.S. producers but are divisions of larger companies, not standalone investments; (2) independent original-equipment (OE) component suppliers such as BorgWarner, PHINIA, Tenneco, Garrett Motion, and Mahle; and (3) aftermarket parts makers and remanufacturers such as Standard Motor Products and Dorman Products [3][4].

3. Size (this level's rollup figures)

Because there is one child, the level's totals are the child's totals. These are our ground-truth federal figures for NAICS 33631:

Reading the concentration numbers. The top four firms make about 46% of shipments and the top twenty make 82% [1], so this is a top-heavy industry of large plants. Yet the HHI — a standard concentration gauge on which the U.S. Department of Justice treats below 1,000 as unconcentrated — is only 663 [1], meaning no single firm dominates. A handful of big producers (the automakers' own engine plants and the largest tier-one suppliers) sit above a long tail of ~600 smaller machine shops, casters, and rebuilders. The Small Business Administration draws its small-business line unusually high, at 1,050 employees [7], which is itself a signal of how capital- and labor-intensive engine work is.

Employment is falling faster than output. Headcount dropped from 61,615 in 2023 [5] to 52,700 in May 2026 [6] — roughly 14% — reflecting consolidation and the early effects of powertrain-mix shifts. The two numbers come from different federal surveys (an establishment census versus a monthly employment series), so the level is more reliable than the precise rate of change; read the direction, not the decimal.

Undercount caveat. Engine manufacturing is well captured by the business census — it is large-plant, incorporated, payroll-employing work, not the sole-proprietor or government activity the census tends to miss. Two honest subtleties remain. First, a large share of U.S. gasoline-engine value is embedded inside vertically integrated automakers whose primary classification is vehicle assembly (NAICS 336111/336112), so this code understates the total economic activity of "making engines" in America. Second, these are domestic-production figures; a substantial volume of engines and engine parts is imported, so U.S. consumption of this category exceeds the ~$39 billion produced here [1].

4. Investable universe (where value concentrates)

With only one child, there is nowhere for value to "sit" other than 336310 — so the map is the same as the leaf's. There is no listed pure-play U.S. gasoline-engine maker. The closest public exposures are component and aftermarket suppliers whose revenues blend combustion, hybrid, and EV content: BorgWarner (NYSE: BWA), at roughly $14.3 billion of FY2025 sales with 82% of revenue in its combustion-and-hybrid "Foundational" business and 18% in eProducts [8]; PHINIA (NYSE: PHIN), the ICE-focused 2023 spinoff from BorgWarner, at roughly $3.5 billion [9]; and Garrett Motion (NYSE: GTX) for turbocharger-specific exposure [10]. For aftermarket exposure tied to the installed fleet rather than new-car build rates, the names are Dorman Products (NASDAQ: DORM) at ~$2.0 billion and Standard Motor Products (NYSE: SMP) at ~$1.5 billion [11][12]. Those are total-company revenues, not the U.S.-336310 slice — no listed company reports at this NAICS boundary.

The largest engine-parts platforms remain privately held — Tenneco (Apollo-owned since 2022) and Mahle (foundation-owned) — which is why private capital has been the more active owner in this industry [3]. See the 336310 primer for the full company table, the competitor set, and the diligence checklist for private buyers.

5. How the money works

The economics are the child's economics. This is classic cyclical manufacturing, where owners make money on volume, capacity utilization, and content per engine. Two revenue streams differ sharply: OE sales run on multi-year platform contracts at thin single-digit operating margins with contractual annual price-downs, while aftermarket sales are higher-margin and steadier, priced on catalog breadth rather than build volume. Heavy fixed costs (casting, forging, precision machining) make profit highly sensitive to plant utilization, so earnings track vehicle-production cycles closely.

The revised child primer now puts numbers on that shape, using diversified suppliers as proxies because no NAICS-level margin data exists. BorgWarner reported a 2025 gross margin of 18.7%, a GAAP operating margin of 3.7%, and an adjusted operating margin of 10.7% — the gap driven by impairment and restructuring items [14]; PHINIA reported $762 million of gross profit and $254 million of operating income on $3.5 billion of sales, roughly a 22% gross margin [9]. Customer concentration is measurable rather than merely asserted: BorgWarner's ten largest customers were 71% of 2025 sales, with Volkswagen at 13% and Ford at 12% [8]. So is trade cost — 2025 tariffs on steel, aluminum, and auto parts added an estimated ~$30 billion across the auto industry [13], and BorgWarner alone booked $108 million of incremental tariff expense on approximately $918 million of imports, 68% of that value originating in Mexico [8].

Tighter efficiency rules add hardware — turbochargers, direct injection, variable valve timing — raising the dollar content a supplier sells per engine even as engine volumes plateau. The large, aging vehicle fleet provides a recession-resistant aftermarket cushion [2]. Full detail is in the 336310 primer.

6. Demand drivers

• U.S. light-vehicle production — OE engine-parts demand rises and falls with vehicle build rates. Sales ran at roughly a 16-million-unit annualized pace in the first half of 2025, easing toward ~14 million in the second half [15]; domestic auto and light-truck assemblies were at a 10.48-million-unit seasonally adjusted annual rate in June 2026 [16].
• The ICE-versus-electric mix — ICE vehicles were about 74% of new U.S. sales in early 2025, down from more than 97% in 2016 [17]. Roughly 22% of 2025 light-duty sales were hybrids, battery-electric, or plug-in hybrids combined, with battery-electric and plug-in models together about 9% [18]. Each point lost to fully electric vehicles is a point of lost gasoline-engine demand.
• The installed base lags the sales mix badly — battery-electric vehicles were only 2% of the registered U.S. light-duty fleet in 2024 [18]. This is the single most under-appreciated fact at this level: even a fast sales transition leaves an overwhelmingly combustion-powered fleet to service for decades.
• Hybrids — still contain a gasoline engine, and rising hybrid share is the most important near-term support for the industry [19]. Garrett Motion projects light-vehicle gasoline turbocharger penetration growing until 2032 and staying above its 2020 level beyond 2036 [10].
• The installed fleet (aftermarket) — 289 million aging vehicles drive durable replacement demand independent of new-car cycles [2].
• Fuel prices and miles driven — influence both new-vehicle mix and aftermarket wear.

7. Regulation

Federal efficiency and emissions rules are the dominant policy variable, and the trajectory reversed in 2025–2026 — this is the largest substantive change at this level. In February 2026 the EPA finalized the rescission of the federal greenhouse-gas endangerment finding and the vehicle GHG standards that depended on it [20], while stating that traditional-air-pollutant requirements were not removed [21]. The National Highway Traffic Safety Administration's 2024 Corporate Average Fuel Economy (CAFE) rule — about 2% per year for model years 2027–2031 — remains the published final rule, but a replacement was proposed in December 2025 and had not been finalized as of mid-2026 [22][23]. Congressional resolutions signed in June 2025 disapproved the California waivers underpinning Advanced Clean Cars II [24], and California continues to litigate [25]. The federal EV consumer tax credit ended after September 30, 2025 [17].

The net effect cuts both ways for owners of this industry. The most binding federal electrification pressure is gone, which extends the runway for gasoline engines beyond what the 2024 rules implied. But tighter rules were also what forced efficiency hardware onto each engine and raised supplier dollar-content per unit, so relief is not unambiguously good news for content growth. And the reversals themselves are a cost: repeated policy swings shorten planning visibility and complicate powertrain capital allocation. See the 336310 primer for the regulatory detail.

8. Consolidation

The engine-parts tier has been consolidating and re-sorting for a decade to separate declining-ICE assets from growth-EV assets: Tenneco absorbed Federal-Mogul's powertrain business (2018) and was then taken private by Apollo Global Management in a ~$7.1 billion deal (2022) [3], pulling the largest engine-parts platform off the public market; BorgWarner bought Delphi Technologies (2020) and spun off its fuel-systems and aftermarket business as PHINIA (2023) [26] — a deliberate split of combustion cash cow from electrification growth; and aftermarket names such as Standard Motor Products (Nissens, ~$388 million, 2024) and Dorman continue to roll up parts coverage [11][12]. The result is a barbell of a few global tier-one suppliers, the automakers' captive plants, and a long tail of smaller shops, with competition increasingly turning on which suppliers can fund both ICE obligations and the EV pivot at once. Full narrative in the 336310 primer.

9. Risks

• Secular EV transition — pure electric vehicles need no gasoline engine and far fewer engine parts; every share point ceded to EVs permanently shrinks the addressable market. The substitution is nonlinear: a battery-electric vehicle removes nearly all gasoline-engine content, while a hybrid preserves most of it.
• Cyclicality — thin OE margins and high fixed costs make earnings swing hard with vehicle-production cycles.
• Customer concentration and price-downs — a few automakers buy most OE output and impose annual price cuts; BorgWarner's top ten customers were 71% of 2025 sales [8].
• Input costs and tariffs — 2025 steel, aluminum, and auto-parts tariffs squeeze already-tight supplier margins [13][8].
• Labor — skilled-machinist scarcity, wage inflation, and customer shutdowns are operational risks; BorgWarner cites the production disruption from the 2023 UAW strikes at Ford, General Motors, and Stellantis [8].
• Regulatory volatility — repeated federal reversals complicate long-term capital allocation even when the immediate direction favors the industry.
• Stranded-asset risk — ICE-specific tooling could be stranded if electrification re-accelerates.
• Aftermarket cushioned but not immune — as EVs age into the repair market, engine-specific aftermarket content declines [2].

10. How to invest & outlook

Public routes. There is no clean U.S. gasoline-engine stock. The practical menu is BorgWarner (BWA) and PHINIA (PHIN) for combustion-and-transition component exposure, Garrett Motion (GTX) for turbocharger-specific exposure, and Dorman (DORM) and Standard Motor Products (SMP) for aftermarket exposure geared to the installed fleet. Judge each by how much of its revenue is tied to declining pure-ICE content versus hybrids, EVs, and aftermarket [8][9][10][11][12].

Private routes. This is where control ownership concentrates — private equity (Apollo's Tenneco) and family/foundation ownership (Mahle) hold the largest engine-parts platforms; opportunities run to tier-one buyouts, aftermarket and remanufacturing roll-ups, and specialized casting/machining shops in the long tail [3]. The child primer's diligence note is worth carrying up to this level: a seller's "powertrain" revenue should never be accepted as equivalent to this NAICS without a product-level bridge.

Outlook (forward-looking judgment). The bear thesis of terminal ICE decline has softened materially. EV adoption has slowed, the federal EV tax credit ended in late 2025 [17], the EPA rescinded its vehicle GHG standards in February 2026 [20], and buyers are leaning back toward ICE and hybrids [19]. The near-term picture is resilience — flatter, longer ICE volumes than once feared, plus a 289-million-vehicle aftermarket that grows more valuable as the fleet ages [2] and that remains 98% non-battery-electric by registration [18]. The counterweight is visible in the headcount data: employment is already down roughly 14% from 2023 [5][6], so this is a base being harvested rather than grown. Long-term the structural direction is still down for pure gasoline engines, which is why private capital, comfortable underwriting managed decline for cash flow, has been the more natural owner.

For the complete treatment — company-by-company scale, detailed economics, the full regulatory and consolidation history, and sourcing — see the child primer, NAICS 336310.

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Sources

1. U.S. Census Bureau. 2022 Economic Census — Concentration Ratios / Selected Statistics, NAICS 336310 (receipts $38.97B; firms 610; CR4 45.7%, CR8 64.8%, CR20 82.0%, CR50 92.5%; HHI 662.8). 2022. https://data.census.gov
2. S&P Global Mobility. U.S. Vehicle Age Rises Again to 12.8 Years in 2025 (289 million light vehicles in operation). 2025. https://press.spglobal.com/2025-05-21-U-S-Vehicle-Age-Rises-Again-to-12-8-Years-in-2025,-According-to-S-P-Global-Mobility
3. Apollo Global Management. Apollo Funds Complete Acquisition of Tenneco (~$7.1B enterprise value; $20.00/share). 2022. https://www.apollo.com/insights-news/pressreleases/2022/11/apollo-funds-complete-acquisition-of-tenneco-134627289
4. U.S. Census Bureau. NAICS 2022 — 336310 Motor Vehicle Gasoline Engine and Engine Parts Manufacturing (definition and exclusions). 2022. https://www.census.gov/naics/?input=336310
5. U.S. Census Bureau. County Business Patterns 2023, NAICS 336310 (employment 61,615; establishments 696; annual payroll $4.31B; Q1 payroll $1.16B). 2023. https://www.census.gov/programs-surveys/cbp.html
6. U.S. Bureau of Labor Statistics. Establishment Employment, NAICS 336310 (52,700 jobs, May 2026, not seasonally adjusted). 2026. https://www.bls.gov/ces/data/employment-and-earnings/2026/table1b_202605.htm
7. U.S. Small Business Administration. Table of Size Standards (NAICS 336310 = 1,050 employees). 2023. https://www.sba.gov/document/support-table-size-standards
8. BorgWarner Inc. Form 10-K, FY2025 (net sales ~$14.3B; 82% Foundational, 18% eProducts; top-10 customers 71% of sales, Volkswagen 13%, Ford 12%; $108M incremental tariff expense on ~$918M of imports, 68% Mexico; UAW and competitor disclosure). 2026. https://www.sec.gov/Archives/edgar/data/908255/000090825526000011/bwa-20251231.htm
9. PHINIA Inc. Form 10-K, FY2025 (net sales $3.483B; gross profit $762M; operating income $254M). 2026. https://www.sec.gov/Archives/edgar/data/1968915/000196891526000023/phin-20251231.htm
10. Garrett Motion Inc. Form 10-K, FY2025 (gasoline turbocharger penetration forecast to 2032+, citing S&P data). 2026. https://www.sec.gov/Archives/edgar/data/1735707/000173570726000009/gtx-20251231.htm
11. Dorman Products, Inc. Reports Fourth Quarter and Full Year 2024 Results (net sales ~$2.01B). 2025. https://investors.dormanproducts.com/news/news-details/2025/Dorman-Products-Inc.-Reports-Fourth-Quarter-and-Full-Year-2024-Results-Issues-2025-Guidance/default.aspx
12. Standard Motor Products, Inc. Fourth Quarter and 2024 Year-End Results (~$1.46B revenue); SMP Completes Acquisition of Nissens Automotive (~$388M). 2024–2025. https://www.smpcorp.com/newsroom/financial/smp-releases-fourth-quarter-and-2024-year-end-results/
13. Supply Chain Dive / Detroit News. Tariffs on steel and aluminum mean higher costs for the auto industry (~$30B of 2025 industry cost; 25%–50% duties). 2025. https://www.supplychaindive.com/news/trump-tariffs-steel-aluminum-automotive-industry-production/739945/
14. BorgWarner Inc. Press Release: Fourth Quarter and Full Year 2025 Results (gross margin 18.7%; GAAP operating margin 3.7%; adjusted operating margin 10.7%). 2026. https://www.sec.gov/Archives/edgar/data/908255/000090825526000009/a20251231ex991pressrelease.htm
15. Omdia (Informa). June U.S. Light Vehicle Sales — 16.4 Million SAAR (first-half 2025 ~16.2M annualized, easing to ~14.2M). 2025. https://omdia.tech.informa.com/om144346/june-us-light-vehicle-sales-defy-headwinds-with-164-million-saar-but-tariff-risks-loom
16. Federal Reserve. G.17 Industrial Production and Capacity Utilization (domestic auto/light-truck assemblies 10.48M SAAR, June 2026). 2026. https://fred.stlouisfed.org/release/tables?eid=50089&rid=13
17. Alliance for Automotive Innovation. 2025 EV/Get Connected data (ICE ~74% of new U.S. sales vs. >97% in 2016; federal EV tax credit ends 9/30/2025). 2025. https://www.autosinnovate.org/posts/press-release/2025-q2-get-connected-press-release
18. U.S. Energy Information Administration. About 22% of U.S. light-duty vehicle sales in 2025 were hybrids, EVs, or PHEVs (BEV+PHEV ~9% of 2025 sales; BEV 2% of registered fleet in 2024). 2026. https://www.eia.gov/todayinenergy/detail.php?id=67144
19. EY. Global consumers driven back to ICE vehicles as EV enthusiasm cools (50% of buyers intend to purchase ICE; automakers extending ICE/hybrid programs). 2025. https://www.ey.com/en_gl/newsroom/2025/12/global-consumers-driven-back-to-ice-vehicles-as-ev-enthusiasm-cools
20. U.S. Environmental Protection Agency. Final Rule: Rescission of Greenhouse Gas Endangerment Finding and Vehicle GHG Standards. February 2026. https://www.epa.gov/regulations-emissions-vehicles-and-engines/final-rule-rescission-greenhouse-gas-endangerment
21. U.S. Environmental Protection Agency. Fact Sheet: Rescission of GHG Endangerment Finding (traditional-air-pollutant requirements remain). February 2026. https://www.epa.gov/system/files/documents/2026-02/420f26001.pdf
22. National Highway Traffic Safety Administration. Corporate Average Fuel Economy Standards for Model Years 2027 and Beyond (Federal Register; ~2%/yr for MY2027–2031). 2024. https://www.federalregister.gov/documents/2024/06/24/2024-12864/corporate-average-fuel-economy-standards-for-passenger-cars-and-light-trucks-for-model-years-2027
23. National Highway Traffic Safety Administration. CAFE Standards Rulemaking Page (December 2025 proposal; January 2026 hearing). 2025–2026. https://www.nhtsa.gov/corporate-average-fuel-economy/final-rule-cafe-standards-mys-2027-2031-passenger-cars-and-light
24. U.S. Environmental Protection Agency. EPA Transmits Four California Waiver Rules to Congress (congressional disapproval of Advanced Clean Cars II waivers, June 2025). 2025. https://www.epa.gov/newsreleases/epa-fulfills-statutory-obligation-transmitting-four-california-waiver-rules-congress
25. California Attorney General. Attorney General Bonta Files Lawsuit Challenging Trump Administration's Latest Attack on California's Clean Air Standards. 2025. https://oag.ca.gov/news/press-releases/attorney-general-bonta-files-lawsuit-challenging-trump-administrations-latest
26. BorgWarner Inc. BorgWarner Announces Completion of PHINIA Spin-Off. 2023. https://www.prnewswire.com/news-releases/borgwarner-announces-completion-of-phinia-spin-off-301869042.html