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.