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ICCT-led analysis of turbocharged, downsized engine tech finds lower costs and greater benefits than 2012 EPA/NHTSA analysis; 48V, e-boost, Miller

A new white paper published by the International Council on Clean Transportation (ICCT), in collaboration with Eaton, Ricardo, JCI, BorgWarner, Honeywell, and the ITB Group, analyzes current turbocharged, downsized gasoline engine technology developments and trends.

The assessment, which relies on data from publicly available sources and data and information from the participating automotive suppliers, provides an update to the technology assessments performed by US Environmental Protection Agency (EPA) and National Highway Traffic Safety Administration (NHTSA) to inform the 2017–2025 fuel economy and GHG rule.

The technology assessments conducted by the Environmental Protection Agency and the National Highway Traffic Safety Administration to inform the 2017–2025 passenger vehicle fuel economy and greenhouse gas emissions regulations were conducted five years ago. Since then, innovations in vehicle technologies have come rapidly, enabled by computer-aided design tools and electronic engine controls.

Broadly, the detailed analysis of different technologies found that costs are lower and benefits higher than originally determined by the two agencies.

Comparison of ICCT/supplier and EPA/NHTSA costs and benefits of turbocharging and downsizing technologies. This figure, notes ICCT, represents a single pathway for illustrative purposes, but other pathways and combinations are also possible. Source: ICCT. Click to enlarge.

Some of the findings and observations of the study include:

  • There is no need for a 2-stage turbo with e-boost; i.e., the cost of the 2-stage turbo can be subtracted when adding e-boost.

  • The Miller cycle is extremely cost effective, providing a 4-7% reduction in fuel consumption at virtually zero cost once enabling technologies (2-stage turbo or e-boost) have been implemented in the powertrain.

    Miller cycle efficiency increase does not include the potential use of highly-efficient diesel VGTs or improvements in turbocharger design, such as axial flow turbines. Despite the Miller cycle being unforeseen in the rulemaking, it is already in production by at least two manufacturers, and is proliferating rapidly. The reporte suggests that the Miller cycle will likely be on nearly all turbocharged engines by 2025.

  • 48V hybrids are significantly cheaper than the 110V BAS system assessed by the agencies in the rule.

  • Variable compression ratio, another major development, will be in production by 2018.

  • The costs of e-boost are higher than Miller cycle, but there are excellent synergies between e-boost and both Miller cycle and 48V hybrid systems. Overall, e-boost + 48V hybrid systems are expected to provide more than half of the benefits of a full hybrid system at less than half the cost, or a cost of $800–$1,400. They would also enable Miller cycle at no additional cost, resulting in roughly 20-25% reduction in fuel consumption at less than $1,400 compared to the agencies’ turbocharger estimates in the rulemaking, or roughly $35-$70 per percent fuel consumption reduction.

The paper is the third in a series that the ICCT, in collaboration with automotive suppliers, is undertaking to profile and evaluate technological developments in engines, transmissions, vehicle body design and lightweighting, and other measures, with additional focus on costs, benefits and market penetration as well as consumer acceptance issues.




The old dog seems to have quite a bit of life yet ...


Miller might be done with cam phasers at no extra cost.
Put an eCharger on for the low end at small cost.

Brian P

Cam phasers aren't "no" cost, but they are fairly low cost. Most recently designed spark ignition engines have cam phasers on the intake camshaft at a mininum and many have it on both, and it's a common strategy to use them to emulate the Atkinson cycle when operating at part load. They switch to more normal cam timing events when acceleration is demanded.


Most new cars have VVT cam phasers, hence they are no extra cost.

Brian P

They weren't and aren't free. An engine with VVT costs more to manufacture than one without. It has parts that don't exist in a non-VVT version of the same engine, and those weren't made for free. It's low cost ... not free.

It might be "no extra cost" as in, not a line-item option that you have to pay for when placing an order for the car, but that doesn't mean it was free ... it just means you don't have the option of not paying for it.


The engine makers are putting them on most new engines, so I would say they have their reasons. If you are trying to pick a fight, this is the wrong place to do it.

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