View Single Post
Old 05-13-2019, 07:52 PM   #1 (permalink)
Master EcoModder
Ecky's Avatar
Join Date: Dec 2011
Location: Vermont
Posts: 3,968

Gaptooth (retired) - '00 Honda Insight
Team Honda
Gen-1 Insights
90 day: 54.26 mpg (US)

Such Fit - '07 Honda Fit Sport
90 day: 41.27 mpg (US)

Connect - '15 Ford Transit Connect XL
90 day: 25.19 mpg (US)

K-sight - '00 Honda K-sight
Team Honda
90 day: 45.06 mpg (US)
Thanks: 1,729
Thanked 1,682 Times in 1,073 Posts
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?

Last edited by Ecky; 05-13-2019 at 08:58 PM..
  Reply With Quote
The Following 2 Users Say Thank You to Ecky For This Useful Post:
California98Civic (06-12-2019), pgfpro (05-14-2019)