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Ecky 05-13-2019 07:52 PM

Lean burn tuning
Looking to have my car finished within the next week or so (whew, this is a much longer process than my optimistic self anticipated), at which point I'll have the opportunity to start tuning.

I'll start off with two articles I think everyone should read:

Honda's K20A Engine


My (soon to be) ECU is modified by Hondata with their "KPro" system. They have a wonderful piece of software called the "Hondata K series ECU editor" or just "KManager". The ECU supports live tuning and supports monitoring and modification over bluetooth and USB.

If anyone is interested in downloading it just to play with, it's free:

Anyway, to my point of making this thread:

I'm looking for some tuning advice from anyone who has actually tuned for lean burn. My understanding is that peak NOx (and combustion temperature) happens around 15.7:1. This is also peak efficient use of fuel under most circumstances. My (new) O2 sensor is accurate to around 19:1 AFR.

After observing what Honda did with the Insight's stock engine, which runs at 24:1 AFR sometimes, I've extrapolated a few things:

-When running lean, you need to advance ignition timing or the engine begins to skip. I believe this is because flame speed is lower, so you need to start ignition sooner. In the Insight, advance is 20-30 degrees higher at 24:1 than 14.7:1.

-NOx can foul a catalyst. Honda would very occasionally run rich for a few seconds to "purge" the cat.

From other articles I've read:

-Cam timing seems to on average improve fuel economy when advanced, but can't just be assumed. It appears that any changes to intake or exhaust can change resonance in the engine and shift points of optimal timing around.

-Going leaner may or may not improve economy past a certain point. Pumping losses continue to decrease, but BSFC might get worse (for a specific power output) past around 15.7:1. Or it might not.

The main factors I have to play with include:
-Air fuel ratio
-Ignition timing
-Cam timing (-10 to 40)
-VTEC changeover (low vs high cams)
-Engine load

It looks like the "correct" way to tune for fuel economy is to get a dyno that can simulate a partial load and to map out fuel consumption vs load at various RPM, varying ignition timing for each 10 degrees of cam angle. I don't have any good way to access such a dyno, unfortunately, and the process sounds like it could be very involved.

Luckily I *do* get to start with a base map for the engine. Unfortunately, none of the included base maps have been tuned for operation any leaner than 14.7:1, so I have nothing to extrapolate from. It would be nice to get ahold of a map from one of Honda's lean burn engines.

I'd love to hear others' experience with this. How did you do it? What were your results?

oil pan 4 05-13-2019 10:58 PM

If lean will fowl a converter don't run a converter.
I tuned for lean burn on my 7.4l suburban and it worked great, pretty basic but it got the job done.

19bonestock88 05-13-2019 11:07 PM

That’s part of the reason I’m ditching my cat too... that way I can eventually add lean burn

rmay635703 05-14-2019 09:11 AM

Antique 2 way cats like a diesel VW runs can’t foul and are cheap

While running lean a 2 way cat is the best way to decrease VOC, CO, particulate, just not NOx

Erm thinking about it further your running a pollution controlled car with pcv and exhaust gas intake intact, that chart is invalid with an operational pcv and egr

In other words My guess is your stock cat will live a long life and you should log the pollution after your tune, results will likely surprise you

oil pan 4 05-14-2019 10:35 AM

Yeah that's true.
My 454 was not running EGR.

pgfpro 05-14-2019 11:38 PM

I did all my tuning on the road. I think you need to keep the tuning road only because you find out that your aero will play a big part in your maps verse a load type dyno.

Also make sure that you set your eco tuning in open loop if you don't run a cat. When you start running lean burn open loop is your friend. The engine in lean burn is really picky the leaner you go and needs a smooth fuel map. This will keep miss-fire from happening.

Try to keep leaner or richer then 15 to 16:1. Combustion will heat up the exhaust valves in this range. You should be able to be at 19:1+ for light load pretty easily. You will have to calculate anything over 19:1 do to your sensor. Pretty simple airflow verse fuel flow.

You will also learn what rpm the engine likes to be at in lean burn. Every engine has its own rpm that makes its best airflow swirl and tumble. That will also be your highest A/F you can run.

Anyway there is a ton more to it but these are good starting points.

serialk11r 05-26-2019 11:32 PM

I had some limited experience with my Scion FR-S, the engine seemed to have trouble at 17:1 or so. I didn't really mess with the timing much, it's possible that if I really changed ignition timing it could have worked. I gave up entirely when I realized I needed to cheat the post-cat O2 sensor, as it was correcting my wideband calibration while I was driving, so I could only run lean while idle.

I believe your Honda K24 should do a little better because the low-rpm cam has low lift. Still, I think you'll find diminishing returns near the 18 AFR range given your engine is stock. If I had a car and time/money to test it, my thinking is that a significantly increased compression ratio and decreased squish volume would help with lean ignition (using a PCV catch can can buy some knock resistance, and giving up a little timing and power at max load should buy a bit more).

KnifeKnut 06-12-2019 07:52 AM

In piston aircraft this is called Lean Over Peak

They lean out the mixture until they are well past the peak exhaust gas temperature. Running too close and too long to peak EGT will fry the pistons.

I admit I am a total noob to the subject, but I think it would be a good idea to add exhaust gas temperature instrumentation just as an extra engine health safety measure, and another data point to look at, not to mention a way of directly seeing just how lean you are truly running.

Not fair that aircraft get all that wonderful instrumentation, and we don't on modern cars. We claw back some of those gauges with scangauge and the like.

rmay635703 06-12-2019 08:00 AM

Aircraft run at WOT then use leaning out to set their speed that is very different than lean burn in a car at partial throttle

In Eckies case running at WOT at 15.5 -1 would likely drive him over 100mph

oil pan 4 06-12-2019 01:41 PM

It will also burn and pit the exhaust valves.
I did this to an engine back around 2001.
Pistons were fine. The exhaust valves were fried.
But I made the mistake of lean at wot.

In my 454 suburban it was rich at wot, lean the rest of the time. Tore down the engine after 9 months of running it that way and the Pistons and exhaust valves were fine.

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