How much does emissions kill MPG?
Cargo Master
Joined: Aug 2004
Posts: 2,899
Likes: 2
From: Lynnwood, WA
Problem is, efficiency depends on peak temperature, not compression.
Post Fiend
Joined: Jun 2001
Posts: 5,228
Likes: 5
From: Running Springs CA
Compression is a major factor in efficiency. One of the key variables for an Otto cycle engine is compression ratio. That is one of the reasons diesel engines are inherently more efficient. When gasoline engines went from flathead designs at 6-7:1 to OHV at 8-10:1 in the 1950's efficiency went up. That increased efficiency was masked by bigger engine sizes, much better acceleration, heavier cars, and early automatic transmissions.
We have kind of repeated that in the last decade or so. Modern multi-valve OHC engines with high compression ratios can run well on 87 octane. Instead of more mpg, our cars and trucks got faster and heavier at the same time.
Jim
We have kind of repeated that in the last decade or so. Modern multi-valve OHC engines with high compression ratios can run well on 87 octane. Instead of more mpg, our cars and trucks got faster and heavier at the same time.
Jim
Super Moderator
Joined: Apr 2004
Posts: 34,533
Likes: 2,835
Uhh, don't feel that way. It was not my intention to do that if I did.
There is a basic level of the "science" behind this stuff, and then the various mfg adapt it to their engine lines, sometimes with different methods on different engines. Most folks have more questions than answers. And face it, unless someone is an engineer working on this stuff, or a tech that services it, most people are just reporting what they've read.
You can google search this stuff, check "Wickipedia" and "Howstuffworks"
Howstuffworks "Search"
Then, you can move on to SAE papers, and then international stuff.... it never ends.
It's the internet, you're ok.
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