Lean tune for highway economy

[CoZZm0]

Hi guys.

Car background: SR20VE '20V' (11:1 comp), stock intake & airbox, stock headers to the cat, 2.25" mandel bent exhaust, magnaflow muffler & resonator, with a 6speed gearbox. Always filled with 98ron, usually 2 tanks a week (yeh, i drive a lot). Last dyno reported 118KW.

Funny story really ... i had a bad connection on my wideband (LC1) gauge and it would intermittantly show ~20.8 instead of 21.8 as the leanest value. It wasn't until today that i had my laptop plugged in to do some logs on the highway to see what cells were getting used and i saw nistune recording 16.5:1 AFR's instead of 15.5:1 as my gauge was reading.

Now, this brings on an interesting question. Keep in mind, this is all STRICTLY light load cenarios.

My K-Value isn't correct, i've figured that much as when i unplug O2 Input the car goes lean, but its still totally driveable. I do want to sort it, but that will involve tweaking the rest to avoid it being too rich (as its OK at the moment) AFR's under load are still nice around the 12-13 range.

Low load driving around AFRs can peak (very briefly) at 16.8:1 with only minor / slight hesitation, so its showing the point of there not being enough fuel. Which i can understand! No audible knock has occured at all during this time (exhaust isn't very loud so i can hear it).

I do a fair amount of highway stuff, and mostly i cruise around during the day.

Looking to improve fuel economy, but wanting to make sure that i don't do any damage to the motor at the same time.


So the question really is ...

Is it "safe" to tune the car lean (switch off O2 flags on selected cells) and at what target would be considered 'safe', but still worthwhile for an impact on fuel economy.

Does timing have a massive influence on the exhaust temps at low load situations. At this point advance is still around 30deg

Have i been very lucky to have not made a molten VVL coffee table ?


Cheers.


P.S i was having lots of problem with nistune freezing after about 1 minute or so, somtimes randomly after only doing some simple operation like adjusting a target idle speed at a couple of points, thought it was my laptop ram etc etc. Updated the FTDI drivers for my ECUTalk USB cable and i was able to capture a 15 minute log without a hiccup with the LC1 AFR input via Serial to USB converter as well.

[raddy]

for sure, you can use fairly lean mixture for low loads...Im using AFR of about 17:1 in my ca18det, but be sure that AFR goes richer immediately as you press pedal little more. as soon as load even slightly increase, you have to use more fuel, about 15:1 ideally. in my case Im using mentioned lean mixture up to about 130km/h at 5th gear...

each engine accept different AFR leaning, in my case I get hesitation at about 18,5:1, but some engines doesnt accept more than about 16:1...

EGT is highest at 14.7:1, with lean mixture is EGT decreasing so knock is no problem here-but again, low load is condition.