Lean burn tuning

[VikingCX]

Originally Posted by Ecky

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

Don't get super tunneled on the AFRs. There's more to the picture than just the AFR that you can tune around.

If the engine is DBW you can rework the throttle maps to allow greater throttle openings while maintaining the fuel flow rate. That will allow you to adjust the throttle (read: airflow / VE) to where the engine will tolerate it.

Advancing the intake cam has less to do with resonance and wave tuning and everything to do with increasing dynamic compression. The intake valve is closing sooner, so you are compressing a larger swept volume into the clearance / chamber volume. This means there will be greater compressive heating, so mind the ignition advance.

Running lean has everything to do with mixture homogeneity and fuel sensitivity. The more heat you can put into the endgas the more likely you are to not misfire, although the closer you are to pre-ignition and detonation. Also, port flow turbidity and swirl will count. This is all dependent on flow velocity, which you'll be able to "see" in the VE map. Cam switching (and somewhat timing) will affect this too.

If your K-series has a full exhaust manifold, you can gain some improvements in scavenging and reduce the valve heating. That will take some effort. Beryllium valve guides and seats are for the bold ... haha.

[serialk11r]

Hey Ecky, thought I'd ask in this thread to be more on topic, did you manage to make lean burn work with only Hondata Kpro? Is it open loop lean?

I'm still eyeing an S2000, which I think doesn't have Hondata Flashpro available for pre 2006 models but a Kpro might be worth the investment. A wideband O2 emulator will get the job done but it would be nice to keep more of the stock tables.

[Ecky]

I'm running closed loop lean, but I'm uncertain my ignition timing is perfect. I need to get either some dyno time or get my cruise working and find some long, flat roads. There's also a bug in KPro which is a bit annoying:

In KPro you need to set a target lambda upper limit - by default this is 14.64:1. You then have a table where you can set lambda per cell, at every given MAP and RPM value. If it worked exactly as it appears, it would be great. However, let's say I set a target lambda limit of 15.7:1, and one row on my table looks like this:

2000RPM
100mbar - 15.7:1
200mbar - 15.7:1
300mbar - 15.7:1
400mbar - 15.7:1
500mbar - 15.5:1
600mbar - 14.7:1
700mbar - 14.6:1
800mbar - 14.2:1
900mbar - 13.5:1
1000mbar - 13.2:1
(Just an example to show the bug, not exactly what I'm running)

I then set it to stay in closed loop until 900mbar.

What I'll actually get is this:

100mbar - 15.7:1
200mbar - 15.7:1
300mbar - 15.7:1
400mbar - 15.7:1
500mbar - 15.5:1
600mbar - 15.7:1
700mbar - 15.7:1
800mbar - 14.2:1
900mbar - 13.5:1
1000mbar - 13.2:1

What it seems to do is take any value on the AFR table around stoich and just use the lambda limit instead. E.g If I set 15.0 in a closed loop cell I'll get 15.0, but try to run 14.5-14.9 and it jumps back up to 15.7. 14.2:1 will, however, still work in closed loop.

My choices then are to:

1) run lean at a higher load than I'd like,
2) go slightly rich at lower loads where I really just want 14.7,
3) go open loop at a lower load than I'd like

I've filed a big report, but the feedback I was given from Hondata was basically "DO NOT DO WHAT YOU'RE TRYING TO DO, YOU'RE GOING TO DESTROY YOUR ENGINE."

[serialk11r]

Ah okay. I'd just go open loop at a lower MAP if you're worried. 700mbar is not that high though, I think your engine will be fine. I really don't think burning anything up is an issue, because engines running with cooled EGR have even slower burning mixtures. The peak flame temperature theoretically increases, but you have less and slower heat release so there isn't as much heat for the piston to absorb in the first place.

It would help to raise your compression ratio to provide a blanket increase in combustion speed to compensate for the slower lean burn but I suppose that's not an option.

For my future S2k I might just use a narrowband emulator and run modestly lean to make things easy. The issue with that engine is the stock tune runs at ~13 AFR at WOT, so there's not a lot of room to lean it out for cruising, maybe 5% at best, which is incidentally about where ignition timing needs to be changed before efficiency drops.

[Ecky]

Originally Posted by serialk11r

Ah okay. I'd just go open loop at a lower MAP if you're worried. 700mbar is not that high though, I think your engine will be fine. I really don't think burning anything up is an issue, because engines running with cooled EGR have even slower burning mixtures. The peak flame temperature theoretically increases, but you have less and slower heat release so there isn't as much heat for the piston to absorb in the first place.

That's what I was thinking, but it's good to have that reinforced.


[QUOTE=serialk11r;621493]It would help to raise your compression ratio to provide a blanket increase in combustion speed to compensate for the slower lean burn but I suppose that's not an option. [quote]

The easiest way to bump compression would be with a thinner head gasket, but the piston-valve clearance is already extremely close. I'd probably want to replace the pistons with some that have deeper reliefs. So, not an option.

Originally Posted by serialk11r

For my future S2k I might just use a narrowband emulator and run modestly lean to make things easy. The issue with that engine is the stock tune runs at ~13 AFR at WOT, so there's not a lot of room to lean it out for cruising, maybe 5% at best, which is incidentally about where ignition timing needs to be changed before efficiency drops.

Seems reasonable!

I'd love an S2000 but prices are beyond silly. For similar money, I think I'd take a K-swapped Miata right now. Have your eye on one in particular?

[serialk11r]

Another way to think about lean burn and piston damage is that the momentary high temperature in the cylinder is higher in a turbocharged engine and MUCH higher in engines running N2O, but they take a long time to melt at WOT. If you're just running at part throttle lean, the peak temperature could be a touch higher, but the cylinder walls/head/piston will quickly bring the temperature down since the lower density gas has less absolute heat capacity.

If the tiny variation in peak combustion temperature mattered so much, then running hydrogen or straight gasoline instead of E10 would melt pistons too. It doesn't. The peak temperature of the flame is always much higher than the melting point of any of the materials in the engine, but the engine is spinning quickly and any part of the engine is only momentarily exposed to the high temperatures, so the average temperature matters more. Lean burn reduces the average temperature since there's less heat in the first place.

People also like to mention oil consumption, but again, IIRC engines running stoich already have ~2% unburned fraction, so there's already some free hot oxygen available to burn oil, you're just making that reaction go a little faster. I don't think combustion of oil is the primary way that engines lose oil anyhow.

Yea S2000 prices are silly, but I really should not be spending time dealing with modified cars, so I just want to find a bone stock car. Last year there were several cars with minor damage going for below 8k, I'm hoping I can snag one like that. With the economic downturn coming, I figure some dents and minor rust would help me blend into the proletariat :P

[JulianEdgar]

My experience:

- You need really, really good ECU control and mapping to do lean burn well

- Forget about worrying about EGTs in light load lean cruise - my measurements on the Insight 1 litre show they're nothing to worry about at all.

[ElTruckCarMan]

I would like to add if anyone ever visits here and gets this far...
Lean burn only works in low rpm conditions. if WOT than this is "lugging" in the extreme

the timing must be advanced and the rpms must be low because the flame front is mush slower
but if you are able to "complete" the combustion before the exhaust valve opens you will prevent valve damage and make useful work of energy.

[Drifter]

Originally Posted by Ecky

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.

Does the Insight have a ratcheting parking brake? Even if you wear it out, replacement parts are probably still cheaper than dyno time...

[mpgmike]

Had the opportunity to speak with Bob Krupa a couple times while he was still alive. He told me his '96 T-Bird was leaned out to 30:1 AFR -- EVEN AT WOT!! His Firestorm Plugs were able to ignite the uber lean mixture. Perhaps Pulstar Plugs, or Aquapulser's PDI would facilitate better lean-burn combustion.