Quote:
Originally Posted by E4ODnut
I tune mainly for economy and reliability. Power output is important, but definitely not a priority. I also run open loop only. Some people may prefer to use closed loop but I agree with the camp that says you give up some control with closed loop, and it is often used as an excuse for sloppy tuning. I don't use EGR.
Tuning for best power is relatively easy, and I stress relatively. Best economy is a lot harder.
So far I've found that at loads under ~ 75 KPA MAP, EGTs are not an issue and it is almost impossible to induce detonation with any sane ignition timing. I tune for target AF ratios of between 16:1 and 17:1 below ~ 80 KPA. I reason that with pressures above that I am in need of some serious power and ramp up to ~ 13:1 at ~ 90 KPA and ~ 12:1 at 100 KPA. Some of my engines like it a bit richer, some a bit leaner, but not a whole bunch.
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It sounds like we've learned a lot of the same things.
I almost always work in open-loop, and also almost always with factory ECMs. OLSD - Open Loop Speed Density is my preference.
It sounds as though, like me, you realized a long time ago that there is almost never a time during normal driving when 14.6:1 is the ideal AFR.
The reality is that it (14.6:1) is a window of predictable operation set in order to be able to guaranty that emissions can also be maintained within a certain window in order to satisfy the EPA requirement.
That fact that it is the stoichiometrically correct ratio for gasoline is for all practical purposes irrelevant.
In closed-loop, for at least 99% of your driving the burn speed of the air/fuel charge does not match the speed of the piston very closely. That's why a tuner can come in with an open-loop tune and make such huge improvements in both power and economy.
I also find economy tuning to be a bigger challenge than power tuning.
To tie this back to the subject of this thread, one problem with the BSFC maps that members here are using to guide their driving is that enough specifics aren't given with the maps to know what is actually going on there. The maps are plotted with load vs RPM, which is fine, but if you assume a constant AFR or spark lead, then the map becomes much less useful. If spark and AFR are optimized for each load cell, then they need to specify this. It's pretty obvious that a factory calibration could not hold an AFR of 14.6:1 at some of the higher loads on the map for any extended amount of time without having to adjust the spark due to cumulative heat build-up in the chamber. If the spark changes, then the adaptive fueling would also adjust via fuel trimming. They don't say the loading intervals or what engine management system was used to create the maps.
To me the BSFC map is almost useless.
Also, the idea about removing the throttle being a source for significant improvement in efficiency is false. I can understand people looking at everything in order to get the last bits of efficiency, but this situation is like tripping over dollars to look for a penny.
Variable valve control, in a very sophisticated form could allow removal of the throttle blade, but at that point the pressure differential and restriction is just shifted from the throttle to the intake valve.
And anyway, even if you could remove all the restriction, gasoline can not effectively burn over a wide range of AFRs that would be required. By effectively I mean that yes you can burn gasoline very lean, but you cannot then load the engine down. You can with diesel, but not gasoline.
The diagrams from the EPA should make it clear the small amount of efficiency that is listed under pumping loss. Once you find and quantify all of the sources of energy lost under this category, you would find several sources that dwarf the air-flow restriction caused by the throttle.
I'm not sure why this perspective has been completely lost in this discussion.