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Old 02-26-2012, 05:17 PM   #10 (permalink)
Cyborg ECU
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Join Date: Mar 2011
Location: Coastal Southern California
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Black and Green - '98 Honda Civic DX Coupe
Team Honda
90 day: 66.42 mpg (US)

Black and Red - '00 Nashbar Custom built eBike
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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:

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.
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.
Originally Posted by viio View Post
Some great reading here on back pressure:

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