[Ecky]

Originally Posted by mpgmike

I just spun my wheels for the past hour trying to look up fuel economy ratings for similar vehicles offered in the US, NZ, AU, and EU. Sadly, for some vehicles, I can easily find fuel economy ratings for the US, but not other areas, or the other way around.

I had a similar question arise in a US Federal court case (where I became officially recognized as a Fuel Economy Expert) back in 2008. Back then, I was more easily able to look at the VW Jetta Diesel, Subaru Outback, and other global models to compare regional fuel economy ratings. What I found was the US versions ALWAYS got the worst fuel economy. European models faired 10-20% better than the US. AU/NZ models were rated at 20% to a whopping 70% better fuel economy. (Specifically, Volkswagen had their Blue Diamond Diesel engine that was getting the equivalent of 72 US MPG Down Under versus 42 MPG in the US in the Jetta!)

This begs the question; do NZ/AU versions get worse emissions, or do US versions leave a lot on the table??

Though I cannot verify this, a friend of mine spoke with a Toyota engineer that claimed they can get well over 200 MPG US in their Camry (in the lab), AND MEET EPA EMISSIONS STANDARDS OF MAXIMUM EMITTED EMISSIONS TOXINS! However, the EPA tells them what fuel delivery system they must use, that they have to use specified catalytic converters, what software limitations they must stay within.... All evidence suggests the EPA has mandated a maximum fuel economy capability that must be enforced by the ECU -- at least in the US.

From the minor amount of research I've done, most overseas markets have looser emissions standards, so that accounts for part of it. One example, the US 2001-2006 Honda Insight automatic runs at stoichiometric air fuel ratios, whereas in Japan it leaned out to nearly a 25:1 AFR. Folks who have installed JDM ECUs in their USDM cars have seen as much as a 20mpg improvement (65 -> 85mpg) under certain conditions. The manual transmission Insight can do this in the US, but it meets a looser emission standard (Ultra Low Emissions) rather than the Super Ultra Low Emissions the automatic meets, because in order to get that kind of economy, the engine ran dirtier. Emissions are considerably worse when running in lean burn, even with the addition of a second catalyst to neutralize some of them. That adds cost to the car, and I'm sure there's some penalty for selling a more polluting vehicle.

Part of it is that the engines themselves are different. Two examples: The Mazda Miata in Japan, NZ and AU have a 1.5L engine, whereas in the US we got a 2.0L. The smaller displacement NZ model is rated for 49mpg highway. The 2.0L from the US car was later introduced to their market, and is rated for the same 35mpg highway there as it is here. Additionally, most of Europe and Asia get a Honda Fit (Jazz) with a 1.3 or 1.4L engine, whereas it comes with a 1.5L in the US, as well as shorter gearing. The explanation from Honda is that US customers have different expectations. One being, that 35mpg is enough, and another that a 1.3L four with a tall transmission would be dog slow and not worth buying, no matter how good it is on gas.

I do engine tuning myself. There is no magic 200mpg tune. All of the variables are exposed in my car's ECU, and you can change them and see what happens. You choose how much fuel to inject, you choose when spark happens. On some engines you can phase the camshaft or vary valve lift and duration. Changing these variables DOES affect fuel economy - AND emissions. You can sometimes squeeze another few mpg out by tuning the engine differently, but emissions are increased.