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Old 02-26-2012, 05:17 PM   #10 (permalink)
California98Civic
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Join Date: Mar 2011
Location: Coastal Southern California
Posts: 6,128

Black and Green - '98 Honda Civic DX Coupe
Team Honda
90 day: 66.42 mpg (US)

Black and Red - '00 Nashbar Custom built eBike
90 day: 3671.43 mpg (US)
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Quote:
Originally Posted by Ladogaboy View Post
I want to add something to Post #8. What oil pan 4 was saying in regards to diesel turbos "loving their cylinders stuffed with air" would apply to at least some gas turbos. I was doing some more research on my car's tuning, and its AFR range is from 9-11:1 from factory. By eliminating back pressure in the exhaust, the AFR does improve. I'm not sure how much fuel efficiency can by gained by increasing from, say, a 10:1 AFR to a 12:1 AFR, but that seems to be a pretty common shift.
I added this point, and all of these:

Quote:
Originally Posted by oil pan 4 View Post
About the only application where adding larger pipe and muffler or removing the muffler is going to help will be a turbo diesel.
Turbos like as little back pressure as possible and diesel engines love having their cylinders stuffed with air mass even at light load.
Quote:
Originally Posted by Ladogaboy View Post
Elimination of back pressure has benefits in gas turbocharged engines as well, but top-end power is where this is primarily seen. In regards to fuel economy, I don't know of any proven effects either way.
Quote:
Originally Posted by viio View Post
Some great reading here on back pressure:
http://www.google.co.uk/url?sa=t&rct...ZXjwugSHi3jtxQ

Also a research paper on marine diesel engines which tests and proves that less exhaust back pressure is a good thing on turbo diesels.

http://www.google.co.uk/url?sa=t&rct...6ftTzqrFO90QRw
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.



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