Quote:
Originally Posted by bazman
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My goals are to show that larger engines can still justify their existence. The 5.7 is simply what I have and as I did not want to spend more money on it yet - high boost was not possible on the stock LS...
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I think that's very much a "worthy pursuit". In other words, well worth doing.
Having pushed my admittedly small 1.6 liter engine to nearly 60% above the U.S. EPA's fuel economy estimate, I'm convinced you can considerably increase a large engine's fuel economy if you limit it's revolutions. You burn a LOT of fuel pushing those pistons up and down, and all the other reciprocating action hardware in there too. Valve train components go up and down repeatedly. That's momentum created and destroyed thousands of times per minute.
Anyway, if I were ecomodding a large engine GM car I'd do these things, primarily. Used TOGETHER, I'm convinced they will improve your mpg significantly. And I think this list is the best set of tools you could use for it.
0) Tire pressure. Start with the sidewall max imprint and see if you want to adjust it from there. It's #0 because its basic, in my humble opinion.
1) Manual transmission, with as tall a gear ratio as I could possibly pull together.
2) A kill switch. Kill the injectors so you can coast in neutral with no fuel used. Learning to use it to full advantage might take a while, but well worth it.
3) Aero improvements to reduce the amount of work the engine needs to do in order to make the car move. Having done multiple aero mods on my relatively underpowered car I can now detect the difference in performance.
As for for the manual, with as tall a gear ratio as possible: Give yourself six or seven gears if you can, and a really tall rear end. 5 speeds will work if that's all that's available. With all that power available, if you want to surge forward there will always be a gear that will do it.
A case in point is my little Civic. The HX version has taller gearing than other Civics of the same year, for better fuel economy. If I want it to seriously move out on the highway, I drop it from 5th to 3rd and rev-match at about 4K rpm. That's at about 60 mph or so in my car. Give it fuel and off she goes. If I required big power in 5th at highway speeds, it would have to be geared "shorter" with higher rpms and fuel economy would be worse all around.
Anyway, that's my two cents. I ran on some but hopefully it will be useful.