How lean is too lean at 4k cruising?
 

Asking cause my brain thinks running 16.0 at highway speeds is too lean, should I make it a bit richer? Down to 15.0 maybe?

Id run as lean on the highway as I could get away with.

Run as lean as you can without getting too high egt. You need a lot of timing to run that lean in cruise too.

EGT before or after the turbo? May be something to do down the line.

EGT is measured about an inch from the exhaust port. Its actually something like 1.5x the width of the port.

You can get thermocouples for like $10 on ebay. I'm running mine into a TinyIOx to log with Megasquirt.

I run right at 18:1 for cruise. Lycoming "aircraft" uses a process of leaning the engine to find peak EGT @75% power. Then +100 deg richer EGT for power or -50 deg leaner for best economy. That works out to 18:1 economy and 14.5 power. I have run as lean as 22:1 in the car. PW goes up on mine beyond 17.8 so I settled in at 18 for cruise. I also run 50 deg timing up there. This nets me better than 30mpg at 80/85mph with 4.3 gears. Slowing to 65 ups to 34-35mpg. I do bring it down to 15:1 pretty quickly crossing 70kpa. Running a stock 2001 with MS.
The concern you will have is cylinder balance. The lean to peak applies to the leanest cylinder.
BTW - A high Fuel ratio better than 20:1 does not generate enough heat in EGT to do harm.

Most will say 16:1.

How do you tune timing at cruise. Just raise the timing until the EGTs are safe?

There is no way my 1.6 would push under 70kpa running 18.0, it either won't hit those lean tuned cells, or it will and then quickly jump right back out to higher rich cells. I've tried +/- 10degrees or so around cruise, can't really tell much of a difference. I'm around 40 degrees or so in cruise now.

15.6-15.8 seems to be best for me. There's no way I could run lean as 22.0, pulsewidths would be too small and it would kick and buck like nuts coming in and out of power for hills and stuff. Around 50kpa cruise at 15.8 = 2.9ms

yeah, even with seq. injection and seq. spark, i couldn't cruise leaner than 16:1. Anything leaner and it would feel down on power and effect drivability. Maybe if I had better injectors, but 16:1 is the most efficient cruise area for mpgs and that was all I was concerned with.

Save the environment. Run 14.7 like every OEM does in every section of the map except for power enrichment.

'cause NOx?

Yup. Your Cat converter is designed to operate at 14.7. I do calibrations work for a living which involves cert lab emissions. After all the reading and research I've done, I'll always preach that saving 5% on fuel efficiency is not worth the 10x or greater emissions increase.


https://www.miataturbo.net/attachmen...ine=1450113188

what if i care more about 5% gas savings vs. whatever insignificant amount of extra NOx my car makes?

would running lean, then not be "worth it"?


https://www.miataturbo.net/attachmen...ine=1450113372

Then run whatever AFR pleases you. Everyone is entitled till their own opinion.

I'm just stating mine for those who aren't aware how AFR affects post cat emissions. There's a reason why every OEM calibration runs 14.7 pretty much everywhere except WOT.

What if no cat.

i passed emissions, so whatevez.

shiiitttt. I need to pass emissions in march.

Yes, NOx is way up there at lean conditions.

Lets see if I can touch on a few without writing a book. It would not sell well anyway. lol
aidandj- Tuning timing at cruise is pretty simple if you can find a steady state condition. Adjust it and watch PW. Obviously lower PW is better. Timing will affect AFR so keep up with AFR Though timing should always lead the process. Being your car and your motor, go with what you are comfortable with. Note that if you keep leaning the motor, at some point it will peak and go colder as you lean more. Leaning to peak under high power will melt things. I have run 1400 at the turbo for cruise. Timing was too slow then and was at 14.5. Had I added timing and pulled back more fuel EGTs would have dropped.
I have two cars running 18:1 with no problems. the 01 does have stock injectors, but the 95 has 440s. Now I may have some difficultly with 20:1 after putting in my 610ccs for the turbo. But expecting to maintain 18:1. I was showing a friend the MS and set the AFR target to 21.5 once and forgot to set it back. Noticed the next hwy drive the O2 meter was maxed at 20. Laptop was confirmed 21.5. You could not tell by how the car drove. VVT and Tonguerun front lip does help a lot on mileage for me. Car only got 20-21mph stock at 80. So pretty happy with it.

Couple things here on timing. First forums tend to be very conservative on timing. Understandable. However, using the standard for the NA crowd. Stock system runs best with adding 6-8 deg of timing. Well add that to the stock WOT timing of 34 on a 95 and we are in the 40 range under full throttle. Atmosphere pressure (95-100kpa) of course. 37 to 38 would be conservative. Are you guys in that range? Giving 38 100KPA. 45-50 timing at cruise becomes real. I cruise about 50-55KPA at 80. Goes to 65kpa real quick with hills.
I also run my O2 closer to the engine than most. The delay of further down tied to a slower responding O2 is a headache for swinging tune. Leaner as you all know is more critical to have right.

deezum - I expect timing is the reason you are falling out of cruise numbers. Though I do not have experience on the 1.6. fwiw I started where you are with my 01. Was conservative due to 10:1 CR. But once I brought timing up it all fell into place. 01 only likes 34 100KPA where the 95 with 9.5CR has no trouble with 40-42. Take my info with a grain of sand. I also do not run below 25 timing on boost. 12-14psi #3/T04E. I recall comments of more than 17 will destruct... At something like 40k miles on it I figure it is living. Tuning is key as always.

Brain- Yeah hp does drop and at some point 19+ is a losing deal. It will feel softer at 18, but not bad. Beyond 18 and power goes in the tank. Once I cross 75 kpa I add fuel aggressively down to my 13.5. 440cc RX7s in the 95 So not great injectors but they will do it. Do have seq fuel. Needing to do seq ign on both cars. Was able to do 18:1 on the MS1 but a pain to maintain tune with the seasons.

Experience with a bird (O320 160hp Lycoming) having 4 EGTS with 4 O2 sensors has really changed my standards for cruise settings. Lycoming is very well documented on power/tune settings (charts etc). For those not aware it is all manual tune. Fuel adjustment is needed as you change power settings, or altitude, or fly thru a front.

With 3.6 gears going in soon I hope to see in the 40s mpg for 65mph. :party:

Sorry guys. a couple posts past while I wrote my novel. Maybe it is a sign to never write a novel. lol

according to brain's chart (cyotani - your graph cuts off data) my NOx is back down to same as 14.7. CO is lower and HC also looks about the same level. Going leaner to 20:1 does crank up my HC aggressively. Given I am also using 33% less fuel at 18:1 it does sound like the start of a win/win. hmm

Why no cat? I thought this forum loves cats :party:

I'm pretty positive HC goes up because you begin to missfire past 18:1. You don't want to run there. Your economy will be even worse then stoich.

My chart was to show post cat emissions. Look at the solid lines, not the dashed.

I cruise at 14.7:1 because the 5% fuel economy bump isn't worth running the motor at constantly elevated EGTs on the highway.

ok, so pretty sure is not good science. Misfires can happen with sub-pare ignition. Plenty of factory vehicles have had that issue in the past after some time. I am not missing at 21.5 and at really light loads can do 25:1. Had to move my MS range out for EGO to support it. :-) Playing i was able to run 23:1 without trouble in a map area. But noooo power there.

Did you read our comments about better mileage. Yes economy is way better than Stoich.

So on your graph. looking at precat. If my levels pre-cat based on Brains chart are near your pre-cat chart. Then I am "pretty positive" we have a similar post-cat output. And I am still 33% more efficient. 30% less fuel nationwide would make a heck of a dent in gas usage...

Seriously though, since you are in the business. I would really like to see apples to apples. A chart showing PPM for a gallon of fuel. It would be interesting to see how much changes discharge changes with MPG. That chart the way it is used for especially for environmental purposes tells us that a gas vehicle getting 8 mpg (towing less say) at 14.7 is the same atmosphere contamination as a Prius getting 40mpg, a moped getting 80mpg. Or at least as environmentally friendly. Lets talk actual PPM or tonnage numbers for X fuel burnt and see how that unfolds.

None of us are for polluting the air. Well at least most of us are for sure. But the hockey stick perspective is getting old for some. And so without a correct correlation EPA info stats look like the same political science. Non-political science facts seems to fail mainstream and are overruled by a theory. Regardless of how many times the prediction is wrong. Also if we developed a cat to handle the bad juju at 14.7. Maybe we could engineer a cat to handle bad juju at 18:1. A 3% change in fuel consumption has the nation overjoyed or miserable. how would they react about a 10% or 20% less???? Gasoline only of course. But there is a similar discussion to be had on Diesels.

Sorry for the rant guys.

Savinton - the key is to cross over the peak EGT on the lean side. But I can certainly understand your point. I have melted bike pistons just being out of tune. and seem plenty of aluminum showing up on plugs of cars trying to hard for mileage. All carb'd. What I love about EFI is our ability to balance and run safely in areas disastrous with that carb. Timing is important to running that lean and keep EGT temps happy.

Getting back to the OP and keeping this a positive forum. Best to do what you are comfortable with. Running slower timing and lean can cause high EGT. Stay within what you are comfortable with. If my timing info makes sense give it a try and lean accordingly within your EGT numbers. Pick a small section of your table to play with. Like 3500 rpm column and change that range to see results. you can always shift, go faster, or slower to stay out of that tune area until you can change it if needed. If uncomfortable go with the mass knowledge here. None of us are the ones who must fix your motor if it fails. Though we would likely help if close enough. :-)

Sorry for the speculation. I'll back it up with some research.

"HC Emissions also increase in the lean range... The raise within the lean range is caused by incomplete combustion at the extremities of the combustion chamber. Extremely lean mixtures, where combustion lag can ultimately lead to ignition miss, aggravate this effect and produce a dramatic rise in HC emissions. This phenomenon is caused by unequal mixture distribution in the combustion chamber and thus poor ignition conditions in lean-combustion zones."

Source: Gasoline Engine Management published by BOSCH engineering.

Gasoline Engine Management: Systems and
Components (Bosch Professional Automotive Information): Konrad Reif: 9783658039639: Amazon.com: Books


So running too lean causes an un-homogenized mixture which causes incomplete combustion and can cause miss fire.

If you are cruising at a higher AFR and your HC % increases, how can your mpg increase? HC is unburnt and wasted fuel. Your car requires about 25 hp or so to sustain freeway cruise speeds. If you have higher HC emissions that wasted fuel is not making any HP and your MPG goes down. That's why max fuel economy is around 16.0:1 and not over 20.


EDIT:

I challenge you to drive a sustained freeway cruise on a full tank of gas with your 21.5:1 calibration and record the distance traveled. Then change your map to 16.0:1 and burn the same full tank of gas in a similar route and report back on the distance traveled for each tank of gas. If your able to travel further on your 21.5 calibration I'll never post about fuel economy and emissions ever again

We run our FSAE car at 1.3-1.4 lambda, everywhere from cruise to WOT, at all RPM's. This is on a single cylinder bike motor which has been proven to be extremely knock resistant, and this is also with E85. Despite the fact that we rebuild every 20 hours or so, we've seen no damage, had no failures, nothing bad at all. Only 3 first place trophies in fuel efficiency.

We probably should have our own thread or PM on this, but anyway. Yeah I am a little bit familiar with Bosch research. Thank you for the link.

"Extremely lean mixtures, where combustion lag can ultimately lead to ignition miss, aggravate this effect and produce a dramatic rise in HC emissions. This phenomenon is caused by unequal mixture distribution in the combustion chamber and thus poor ignition conditions in lean-combustion zones.""
This is primarily why additional timing is needed. Definitely hotter spark and where a plasma ignition gets pretty cool.

"If you are cruising at a higher AFR and your HC % increases, how can your mpg increase? HC is unburnt and wasted fuel. Your car requires about 25 hp or so to sustain freeway cruise speeds. If you have higher HC emissions that wasted fuel is not making any HP and your MPG goes down. That's why max fuel economy is around 16.0:1 and not over 20."
MPG increases because the engine is unfortunately utilizing very little of the HC to begin with. It is not the only element providing energy. Now I did not state best economy over 20:1. It will drop past 18 on a piston engine. I noted Lycoming has stated their tuning using EGT procedure for best economy. and using that equates to 18:1 on a WB O2 which I have also experienced. I stated I have run leaner which I think is really cool just to be able to. It confirmed for me I was not on the edge of control at 18:1. To be precise. my 01 seems to do best at 17.8. Fact is 14.7 stock netted 21 mpg best and my tune is 32mpg at 80. 65mph went from 25 to 35 mpg using this method.

Here is a chart from Van's Aircraft. Prettier version of Lycoming chart. It shows power drop as you lean. It references EGT ans specific fuel consumption. I can currently only state that correctly mounted EGTs in the aircraft following that curve will result in WB 02 readings of 14.5:1 for max power and 18:1 for economy. Economy must setting only at 65% pwr or less. Earlier I said 75%. Sorry. Any leaner than 18:1 causes more speed decrease than SFC (Fuel Burn) is gained. Also fuel range is critical so max power does take that as well as durability into account. Big Disclaimer. If anything is out of spec, richen to bring maintain within tolerance. CHT, Oil temp, Or if engine starts missing to due to ignition etc...

Very cool!!!!!

21.5 mpg (30 corrected for gasoline) during race conditions, while making about 37 whp (~43 crank) which is 82whp/L (95 hp/L). When tuning for 0.9 lambda, we'd make about 52 whp. So, we lost around 30% power when tuning for lean burn.

I wish I remembered what our lean burn cal made after we turbocharged the motor. I know our power cal made 65 whp with much much more torque than NA.

I run e85 with no cat and I burn lean. My fuel is more carbon neutral and makes less nasty nox on it's own anyway, I don't even feel bad.

I get around 23mpg, which would be ~26-28mpg on 91. Doesn't seem too out of line to me. If leaning out to 16.0 and higher only gets me to 31mpg on 91, oh well, not worth driveability and possible further wear and tear.

I'd get nowhere near 23mpg in race conditions though, that'd be tits....

I get 30+ on 92 when cruising. Cruise AFR is 15.5

my afr target table

https://www.miataturbo.net/attachmen...ine=1450130975

How fast do you drive, because I do 85 min with 4.10s.

I think you have 3.90, right? If you were doing 75 for 30+, I bet we'd be about equal....

Yep. 3.9+6 speed (slightly higher top gear than 5spd) and cruise at 75.

Higher numerically than 5 speed, to clarify. Engine spins faster in 6 speed top gear with same diff gears and travel speed.

Yeah, that.

85 = 4100 rpm for me 5sp/4.10

75 = 3600 for Aidan 6sp/3.90

6 speed w/ 3.63 = 3700@85mph. Do want

85mph speed limit. Do want.

I haz changed 5speed 4.10 for 6speed 3.63 recently. The cruise rpms are a little better. The effing shift gates are a bit too close together. I missed the up shift to 6th twice at Daytona :fawk: but forged plus Supertech doubles saved my ass. The 5speed is better for feel and positive gate location.

I'm getting custom gauges from Revlimiter with the proper graduation for my speedometer to match the gearing of the 3.63.

Then maybe I need to stay with the 5 speed, at least till I totally grenade the 2nd gear syncros...

1-5 is about equal to the old 5 speed 4.10 gearing, right? About like bolting on an extra overdrive gear if I math right.

I was planning on doing the same thing for the speedo, though. Don't care about the odometer, I'll know how far it's off.

This is my commanded afr table. The other reason I was asking, was because at some points, I can watch my AFR go crazy. It will be at 14.0, then 15.1, then 14.8, then shoot up over 16.0, sometimes to 17 or 18.0, then come back down to 14 or so. It does all this in a few seconds time. I think I just need to let it autotune more in that area, maybe EGO is is trying so hard to correct it. Maybe smooth it out better.


https://www.miataturbo.net/attachmen...ine=1450136905

Data logs are a thing for a reason. PID EGO can do that...

Targets like that must mean you are in 1.6 master race. Buy newer injectors and the sequential board, that will save more mpgs than anything.

Yeah you must fix ego. But also should get the map decently close without ego for the end result driver you want. Keep in mind stock ran at 14.7 everywhere but wot. And even in boost you are aggressive. Clean up afr and get ego working right will net you much better cruise

I have 610cc injectors to put in and tune. Will be interesting based on this thread if I still hold my afr numbers. Btw. My cruise low numbers are at 4350 rpm and some kansas winds for mpgs in 30s.