Lean low-load AIR/FUEL for more MPG?

[JethroBodine]

Tygen1 has been doing some experimenting with lean burn and IIRC he says that mildly lean will cause increased EGT, but as you get away from stoich, the temps go back down.

[MeatHead]

Great input from everyone! My plan is to buy a good EGT sensor and rent a load bearing dyno for a day testing these settings. Lets keep the discussion going, good stuff.

Now if only I could try pgfpro's fuel tuning spreadsheet to help me in my findings. I posted in his thread, but no response yet. Soes anyone have and wouldn't mind me trying it? I'm happy to post all my findings and fuel/ignition maps publicly to the community here too.

[E4ODnut]

There's no reason why you can't get the best of both worlds from a boosted engine. It just takes more time tuning and you have to be especially careful when tuning under boost, that's all.

Some people advocate tuning with EGT. I'm not so sure about it. I do know that EGTs can be very handy if there is lots of documentation on what's acceptable and what's not, like on an aircraft engine. However, when you're experimenting on your own, there is none of this information to base your readings on. The temperatures can vary quite a bit from engine to engine, and just where the probe is placed. Having said that, any information is good information because you can document the temperatures under different conditions to compare it to other conditions.

For tuning power under boost I suspect it would be safer to reference exhaust gas oxygen. Start with a rich mixture and work from there because things are more predicable and the sensor response is very fast. This is just an opinion. I have no experience with boosted engines.

Tuning for economy is much safer because if you screw up you aren't likely to hurt anything. It just takes lots of driving under lots of conditions, data logging, and making small changes at a time.

Probably the ideal situation would be to do dyno tuning first, then do the final stuff on the road under real world conditions. I don't have access to a dyno, so it's not an option for me.

[niky]

I've been thinking about buying both an EGT and a wideband for my car to try tuning the lean-burn area, as my car has very good knock resistance at low loads. I've run from 16:1 to 22:1 at times.

Also catless. As long as I pass emissions, I don't need one.

Will be following this thread with interest.

[Ladogaboy]

Originally Posted by E4ODnut

Probably the ideal situation would be to do dyno tuning first, then do the final stuff on the road under real world conditions. I don't have access to a dyno, so it's not an option for me.

Yeah, the dyno tune is done on my end. Under high-load conditions, the best I do is roughly 12:1 AFR. Low-load adjustments will have to be done with that in mind. It seems like the transition points between no boost/boost and low-load timing/high-load timing will be the hairiest.

[MeatHead]

I've tuned a few 4 cylinder honda cars (turbo + na), a turbo nissan v6, and now my car (inline 6, turbo motor). My plan was to apply lean-burn to only vacuum loads, not positive boost load range. Under boost, It will be optimum for power safety (typically around 11:1 afr). Besides, when I press WOT condition I want speed :P!

I've read about some tuners "turning cylinders off" during light load cruising range as well. Does this mean they turn off the injector and spark to certain cylinders during each complete engine cycle? If yes, how feasible is it to combine this with lean burn? By cruising condition, I had in mind those road trips at constant speed/load (typically 60mph range)

[E4ODnut]

"Turning off cylinders" is getting beyond what I am comfortable tuning with. I would think that simply cutting off fuel won't do a great deal of good unless you can also eliminate the pumping losses with some sort of inlet and/or exhaust valve control.

The engines I work with are relatively low tech with stock configuration. My philosophy is one to just try maximize what I've got, tuning to the degree in which I am able to do in real world situations. I just go with the theory that any throttle setting that results in about 80 KPA of manifold pressure or less is "cruise" and I'll run as lean as I can without any sign of lean surge (idle range excepted). For my engines this is about 17:1 indicated. After about 80 KPA I feel that I am requiring some serious power and ramp up to about 12:1 at 100 KPA at max HP RPM. This is just my view on things and what I feel comfortable with. There may be a better way.

[Ladogaboy]

The main reason I could see for shutting off cylinders isn't for efficiency but rather to occasionally cycle cooler air through the cylinders. Doing so could prevent potential damage to engine components, valve seats, etc.

[drmiller100]

A local guy who I respect and trust told me he played with a lean burn B18 honda engine. We compared notes, and arrived at the following recipe

Pretty high compression - he was 12:1.
Do NOT be afraid to advance the timing. A bunch. Like 13 degrees.
Have a knock or det sensor, and respect it.
Do NOT use lean burn over about 20 percent TPS.

He said he got 45-48 mpg out of the vehicle, and running it stoich, it only got 30 or so.

FWIW, From Stoich, if you lean it out a little bit, EGT's will go up for a while, then they will start plumetting.

[drmiller100]

Originally Posted by Ladogaboy

Leaning out the AFR will increase the EGT. The timing wouldn't play much of a role in that; but retarding the timing might prevent you from blowing up a piston. Also, I'm not sure that exceeding ~16:1 AFR will give you much in the way of fuel economy gains. 14.7:1 is stoich (theoretically, a perfect burn off), so you'll probably see diminishing returns by any increase beyond that point.

This is incorrect information.