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Diesel Technology Forum Releases Primer on Retrofits

The Diesel Technology Forum has released a new primer on potential strategies for upgrading existing diesel engines in both on and off-road equipment.

The whitepaper, Retrofitting America’s Diesel Engines, describes the various advantages and strengths of the “five Rs” of emissions reduction: rebuild, refuel, retrofit, repower and replace:

  • Rebuild. After 3 or 4 years, rebuilding some core engine components to manufacturers’ original specifications can return emissions performance to the original design levels. Some manufacturers also have options to improve emissions beyond the original performance levels.

  • Refuel. Use of Ultra-low Sulfur Diesel (ULSD)can lower emissions, as can some other renewable fuels and fuel products such as biodiesel and emulsifiers.

  • Retrofit. The installation of exhaust emissions control technologies such as particulate filters, oxidation catalysts, exhaust gas recirculation (EGR), selective catalytic reduction (SCR) devices, and lean NOx catalysts (LNCs).

  • Repower. Replacing the older engine in diesel-powered equipment with a new or newer diesel engine can dramatically reduce emissions.

  • Replace. Replacing entire vehicles or equipment may be the best option for some of the oldest, heaviest emitting vehicles or equipment due to technological feasibility and cost considerations.

The paper also provides an overview of funding sources for various types of projects, as well as case studies of sample retrofit projects.

Diesel retrofit is highly cost-effective, but one size does not fit all. As noted earlier, several studies have proven that diesel retrofits are extremely cost effective. Some equipment may not be candidates for emissions control devices, but could potentially have emissions reduced through repowering with a newer, cleaner diesel engine. In other cases, engines may be only a few years old and already have some emissions control technology, but can have emissions reduced through selective use of ULSD.

Each retrofit case is unique in terms of its business and its technological environment, but in most cases, a retrofit, broadly defined as one of the 5 Rs, can reduce diesel emissions for virtually all diesel vehicles and equipment purchased before 2007.




Heck, retrofit cars and trucks currently on the road, that are in good-great condition, but with gasoline engines, and 50k to 100,000 miles on the odometer. Many domestics since 1996 also do not have great reliable engines or transmission(there are exceptions, like the ford F-Series), with many GM models prime examples. Combine modern clean turbodiesels (or future Bin2Tier5 diesels) with 5/6 speed transmission, and you just kicked fuel economy up 25-35% from previous gasoline engined figures. It could help companies recoup their diesel R&D and manufacturing retooling costs quicker. A variety of engines and transmissions would have to be offered.

Rafael Seidl

Allen -

converting a car designed for a gasoline engine to one with a diesel requires changes to the suspension as well and is never worth it financially. Besides, you wouldn't get approval from EPA or CARB for anything other than a T2B5 diesel at this point.

Sid Hoffman

You don't have to change the suspension just to do a simple engine swap, especially if you were removing horrible V6's such as GM's 3.1 - 3.8 liter Iron Dukes and putting in modern 4-cylinder turbo diesel engines. Worst case, going to a higher or lower rate front spring is about all you'd have to do. I've seen motor swaps of all sorts, even guys putting V8 engines in Mazda RX7's that had 1.3 liter rotaries. It's not rocket science.


If you're going to swap the whole powertrain (most diesels need a high-torque transmission), does it make sense to go with mere diesel?  PHEV offers more opportunities to e.g. tune the weight distribution (put the batteries wherever you want), and the torque response vs. pedal position can be programmed with a tool over the CAN bus.


I'd say Yes. Most EV rebuilds like those profiled in Homepower are heavy and have a limited range.

I like going 2-3 weeks between fillups on my Jeep CRD.


Hi Rafael,

It really depends on the vehicle in question. As for CARB, diesels are emissions exempt, and I've heard any swap automagically gets that status.


You have been misinformed concerning engine swaps. Any engine swapping must use the same year or newer engine and must still go through emissions testing. Only off-road (race only vehicles, etc) are emissions exempt.

A LS-1 V-8 isn't really that much heavier than a twin turbo RX-7 drivetrain, but the additional torque must be managed. The 350Z's 3.5L V-6 is heavier and larger than a 5.7L LS-1.


Check it out.

Currently, smog inspections are required for all vehicles except diesel powered vehicles, electric, natural gas powered vehicles over 14,000 lbs, hybrids, motorcycles, trailers, or vehicles 1975 and older.

So if I go toss a diesel in my car, I do not have to get it smogged. Not sure about the same year or newer requirement, but I don't think that applies for diesel swaps either, only gassers iirc.

fyi CO2

Would be encouraging to see a retrofit "rebate" as proclaimed in Germany (Dec.3 post)


Well, that would be an interesting way to avoid emissions inspections: Swap to a diesel drivetrain. For others reading the comments in this discussion: They apply to California specifically and the laws of your state should be checked for their emissions control requirements.


Ian, the batteries of PHEV's aren't necessarily heavy.  Also, reducing the required size of the engine to e.g. a 1.3 liter turbodiesel would subtract a great deal of weight.

Rafael Seidl

Yesplease -

diesels may be exempt from smog checks because the PM they emit would could foul the measurement stations. The exemption therefore applies to retrofits of MDV/HDV vehicles that were certified with a diesel to begin with.

This does not, however, mean that the state of California is suddenly going to let you swap out a clean but gas-guzzling gasoline for a frugal but comparatively dirty diesel. The DMV ought not to issue a vehicle license until and unless you can prove the vehicle meets CARB emissions regs, which do not differentiate between engine types.

Obtaining that proof is vastly more expensive than a smog check and frankly, you're not going to be successful without a DPF and NOx aftertreatment. That's precisely why there haven't been any diesel LDVs on the CA market for 20-odd years.


They will allow me to swap out a clean but gas-guzzling gasser for a dirty but frugal diesel. At least for LDVs, which I believe Allen was referring to, and which was what I was referring to. My apologies for an miscommunication on my behalf.

HDVs go through opacity checks annually, and can be checked at weigh stations/checkpoints/etc... for excessive smoke since they represent the majority of diesel powered vehicles in the state, but since the LDV diesel segment is relatively small, CARB decided that it wasn't worth monitoring via smog checks testing opacity. By limiting the sales of new diesels, they've effectively limited diesel emissions from the LDV segment to the point where they don't feel they need to worry about it, and the DMV's regulations regarding these swaps reflect that.


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how long will this emissions loophole stay open in CA
I hope this is true regarding smog checks.

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