Quote:
Originally Posted by Daschicken
As for running lean...Ehh...I would rather add ignition advance before trying to run lean. I don't like the idea of increased NOx emissions either, but I would be all for removing fuel enrichment below 80% load.
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The thing is, on the highway your engine is at low load and that's really when lean burn will help a lot. The other situation is idling, but a real hypermiler turns off the engine :P
The issue with enrichment is that the throttle is configured so that you get a lot more load with a small press of the pedal at low rpm, and you could be inadvertently going into enrichment. It took me a while to discover that despite my best efforts I was still hitting enrichment at 80% load. I have since calculated what the mpg meter should say at the highest load it won't go rich at, and am retraining my foot to step to that way.
Increasing ignition advance isn't going to do jack, but you're right, NOx will increase. If you don't like that, you can still benefit from tuning by increasing EGR or at least knowing about the EGR valve. My wild guess is that your EGR flow rate is knock limited so you can consider modding the valve or something and adding some cooling to it.
My view on NOx is that a large diesel garbage truck or semi or street cleaner is causing way more health damage than a bunch of lean burn passenger cars. If you tune the engine to run a bit richer at high load while maintaining EGR at low load, again, miniscule NOx compared to a diesel truck.