I've been doing some research on cold air & ram air intakes for my truck. I came accross this study done in 2009 at Oak Ridge National Labs. It's for gas engines, so it doesn't really apply to my diesel, but I thought I'd pass it along to my Ecomodder friends who still need the crutch of spark plugs.
The study looked at 4 vehicles:
-2007 Buick Lucerne
-2003 Toyota Camry
-2006 Dodge Charger
-1972 Pontiac Grandville
The first 3 are fuel injected, the last carbureted. Bottom line was that they found the the air filter restriction effect on fuel economy was insignificant on the fuel injected cars, but did hurt the carbureted car. This is because the fuel injected cars have closed-loop control on air-fuel ratio, so you get the same AFR (and intake pressure) regardless of intake restriction.
Here was the take-away quote for me:
Quote:
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Results show that clogging the air filter has no significant effect on the fuel economy of the newer vehicles (all fuel injected with closed-loop control and one equipped with MDS). The engine control systems were able to maintain the desired AFR regardless of intake restrictions, and therefore fuel consumption was not increased. The carbureted engine did show a decrease in fuel economy with increasing restriction. However, the level of restriction required to cause a substantial (10–15%) decrease in fuel economy (such as that cited in the literature) was so severe that the vehicle was almost undrivable.
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Here's the full report:
http://www.fueleconomy.gov/feg/pdfs/...02_26_2009.pdf