Yet another nerd project: milking more mileage

[bmwman91]

1. I have definitely thought about this.  From what I have read, the internal combustion engine is at its most efficient when run a bit lean (equivalence ratio of 0.9, or ~16.3:1).  The amount of ignition advance also influences this.  I will just have to see what happens here when I do this.  So maybe if things turn out to work this way, I will lock the AFR there and still go super lean at idle.  I guess if I REALLY wanted to save gas I would turn the car off at lights and in bad traffic.

2. Exactly.  This would also severely throw off my EGO sensor reading with 50% air running through the exhaust.  A V-motor has a much better setup for this since it is easier to split the exhaust lines and use 2 EGO sensors.

[Alpine003]

1. I have definitely thought about this.  From what I have read, the internal combustion engine is at its most efficient when run a bit lean (equivalence ratio of 0.9, or ~16.3:1).  The amount of ignition advance also influences this.  I will just have to see what happens here when I do this.

This is true but if you want to run at the ragged edge, I would highly recommend an EGT gauge at the least. Most factory programmed ecu's from efficient cars like Honda run very close to 1600 degrees at cruising through maximum advance and very lean afr's. If you go over, say bye bye to your engine.

[bmwman91]

Yeah that's the real issue to balance here.  The Motronic is not designed to run lean like that, so it will not advance the ignition timing much at all during cruising.  That eliminates the big problem with detonation and blown pistons/valves.  At the same time, it might end up requiring me to use more gas to maintain enough power.  It will be interesting to see how this goes.

I am actually thinking of changing the thing, assuming it works.  I might do a directly scalable AFR deal, dependent on TPS.  Like 19:1 t 0% throttle and 16:1 at 40% with adjustable AFR targets based upon the TPS between that range.  Above 14:1 it will just run what it is programmed to normally.

[Alpine003]

Yeah that's the real issue to balance here.  The Motronic is not designed to run lean like that, so it will not advance the ignition timing much at all during cruising.

I really think for maximum efficiency you do have to advance the timing. Have you looked into any piggyback units like the Apex-I ITC? It will intercept the cam/crank signals and send a different value back to the ECU, hence fooling it into thinking it is ahead or behind.

I think using the Apex-I S-AFC in conjunction with the ITC would be a good alternative to any ems or piggy backs since these units are easy to use and setup. Of course there will be some limitations but since they are piggy backs, you won't be starting from scratch as it's just messing with the existing factory program.