I know that the ECU uses closed loop mode for AFR's when you're cruising, so changing those will do nothing, but I've seen razorlab and others say that you can improve MPG's with a tune; I believe with timing. How is this possible? Increasing timing advance a few degrees in closed loop areas of your timing map?

 

Yes. 43 will give you a tad more power (i.e fuel econ) at cruise. The newer 2012 maps have also increased timing a little in those areas.

Mivec helps some too. Again, the newer 2012 maps (in the cruise area) are more like what you should run. They basically advance the cam shaft, which gives more low end torque. To advance the whole cam shaft, we have to have less negative exhaust timing and more positive intake timing. Some overlap helps too, because it allows the piston to suck in some exhaust. i.e. Air that doesn't have oxygen in it. That helps econ by not making the engine pull against vacuum. (Think engine brake)

You can also run open loop at cruise and run a higher AFR. I do this on my car for E85. Last weekend I got 20 mpg on a tank of E85, all highway, 70 mph average. You have to keep an eye on your AFR if you do this. I wouldn't tune someone else's car this way.

 

i wish i could just buy a new front o2 sensor with a rescaled voltage that aimed for 15.3 instead of 14.7

 

Thanks Golden. I wouldn't be able to relax on the highway if I had to be conscious of my AFR's. I'll let the car deal with it, haha. I actually had a turbo honda that was open loop all the time.

I bumped up every cell on my timing map from a 40-43, so we'll see how that goes. I'll try playing with the MIVEC as well. Less exhaust retard and more intake advance in low load cells. Got it.