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Old 02-20-2017, 06:14 PM   #116 (permalink)
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Originally Posted by View Post
The volumetric efficiency section from the same site is also interesting and ties into turbo header design.

Volumetric Efficiency (and the REAL factor: MASS AIRFLOW), by EPI Inc.
These are great in general documents, however I am hesitant to pull a big cummins down to find we would only gain a percent or so at max..
Has anyone modified a big cummins and tested to find firm improvements in fuel efficiency?

A lot of these VE improvements definately do improve horsepower, and sometimes that then has a negative effect on fuel efficiency.
Simple case would be putting a set of extractors on a honda civic..depending on the design you will increase the VE of the engine, and expand the useable rev range by 500rpm, effectively shifting the powerband upwards ..with a corresponding DROP in fuel efficiency due to a sudden torque hole down lower..

I would have thought Cummins would have had this fairly well under control from the factory..(Maybe less so on the earlier engines?)
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