Cruising AFR

[opethmike]

Just curious what everyone has their cruising AFR set to?

[Nicholas R]

When I used to run open loop I would set mine based on my O2 output. I'd try to have it hover around .7v which is a hair richer than stoichiometric AFR (probably closer to 13.5-14.0 or so) but I always felt the performance was better than setting it at .5v. 14.7 is the best ratio for clean burning but 13 or so is best for power. Plus it helped make sure I never ran lean. I'd certainly rather run rich than lean.

If you're running closed loop you have no say in what your AFR is because the lambda system is constantly changing it.

http://www.mummbrothers.com/SRF_Stuff/images/Stoich.gif

[BABIS]

I have just bought the Innovate #3822 kit which has the LC-1 Wideband Controller, AFR Gauge and a Wideband 02 Sensor..

http://img26.imageshack.us/img26/1728/11032013329.jpg
http://img841.imageshack.us/img841/1826/11032013330.jpg

[Bitsyncmaster]

I also have the LC-1 and found you will find 14.7 AFR for cruse is best. Now around town 13.5 AFR will make the engine run better if you don't mine a little less MPG.

[BABIS]

I also have the LC-1 and found you will find 14.7 AFR for cruse is best. Now around town 13.5 AFR will make the engine run better if you don't mine a little less MPG.

very nice to know ;)

[dmc6960]

I tend to cruise a little on the lean side, around 15afr at RPMs less than 2500. 14.7 at cruising speeds above that. Did I mention I get over 30mpg on the highway?

Of course thats the wonderful part about EFI, the moment I hit the gas a little harder I'm instantly at 13.5. Need to be VERY careful when setting such a range though on a car with long cams, if the transition between lean/stoich and rich is not handled properly, you'll get a bouncy little cruiser. Kinda hard on the drivetrain, and tires you our more easily. I still have a lot of smoothing out to do.

[Nicholas R]

I just now realized this was in the EFI section so my comments were rather irrelevant. For my EFI setup, I just let the engine computer do whatever it wants, lol. I'm not going to do a full tune on it until I cam the engine.

[Spittybug]

~13.7 unless the RPMs are above 3,000, then it's 14.0 A little rich. That's .932 and .952 lambda respectively.

I'm thinking I need to reexamine my timing table. I think I feel some very minor "bucking" on closed throttle decel, in the 2,000 RPM range. My advance is at 45* in that range right now.

13* static + ~10* centrifugal equivalent for RPM + ~20* for max vacuum equivalent = 43 So it looks like I may be a bit over advanced and should knock it down. It's not like I need power in that area.....

My centrifugal (RPM based) goes up 20* between 1000 and 3000 rpm (1*/100 rpm linear) and my vacuum equivalent (for charge density) goes from 20* at 53 kpa to 0* at 80 kpa (roughly linearly). This mimics the stock curves including the zero vacuum advance with throttles closed. In my case however, on decel, throttles closed, I'm not zeroing out the vacuum advance..... but I need to lower it.

While the AFR targets you discuss certainly impact the fuel economy, the spark has the most impact on performance.

[Josh]

Just reviving this thread. Im looking into doing some more tuning to get better mileage on the highway.

I was previously getting about 25-26mpg cruising at 14.5 afr, so i bumped it up to 14.8 and Im getting closer to 30mpg.

I would like to get into the 15s but im scared of leaning things out too much. I would just modify the cells that correspond to 2600rpm-2000rpm at fuel loads <45%. This roughly translates to cruising at 110kph.

So what would be things to look for if i set it at say 15.3-15.5 afr? Im scared of melting pistons, and wonderful stuff like that. But im reading guys with sbcs are cruising with afrs up to 17.0!

Interested to hear your guys input.

[opethmike]

I'm cruising in the low 15s without issue.

[Spittybug]

I would love to see your tables guys..... I haven't played with Megasquirt for months since it was running nicely. I'm finishing up my exhaust swap so I've been concentrating on that. The only area of my tune that I wanted to improve was the acceleration enhancement and the hard acceleration from idle. I've never gotten to the "wow" point. I suspect I'm limited by my throttle body size and adapter volume... I don't get the air velocity that I would like to "pack" the cylinders. #1 free up the exhaust. #2 pack the cylinders with the supercharger!!

If you haven't updated to the most recent software versions, I recommend doing so. The enhancements being made, especially to idle settings and warm up are really good.

[Bitsyncmaster]

I tried 15.3 AFR for cruising and found going uphill it was not enough power and had to shift down to fourth gear. So it would depend on your location as to how flat the roads are.

[dmc6960]

I tried 15.3 AFR for cruising and found going uphill it was not enough power and had to shift down to fourth gear. So it would depend on your location as to how flat the roads are.

The beauty of the full range programming EFI gives you compensates for this. When the engine is under a higher load due to the hill it goes into a more rich portion of the map.

Cruising level, 15afr, uh oh, hill, 14afr, yay!

[Josh]

The beauty of the full range programming EFI gives you compensates for this. When the engine is under a higher load due to the hill it goes into a more rich portion of the map.

Cruising level, 15afr, uh oh, hill, 14afr, yay!

Exactly!

Looks like ill bump it up to the low to mid 15s. Im going to do a complete re-do of my afr table, I think this will turn out nicely! Ill post if up when I get back some mpg #s and feel it is running good Owen!

[Josh]

did a complete re-vamp of my afr table and subsequently the fuel ve table. Leaned out the cruise cells alot. Right now in running 15.5 @ 110kph. Havent took it on any extended trips but it my testing it seems to run good. Interested to see my mileage numbers.

Idling at 14afr and sitting in the low 13s to high 12s for WOT.

[lazabby]

Owen made some interesting comments some time back about whether the standard AFR should be at 14.7 since we're using fuel with ethanol. What was the final analysis of that discussion?

[Bitsyncmaster]

Owen made some interesting comments some time back about whether the standard AFR should be at 14.7 since we're using fuel with ethanol. What was the final analysis of that discussion?

It really does not change. The O2 sensor is just reading Lambda 1.00 which it does by not seeing oxygen in the exhaust.

[Spittybug]

IIRC, a Lambda of 1.00 is a way of expressing a stoicheometric burn regardless of what fuel you are using. Gasoline (a mixture with variation, but fairy standard) has an air fuel ratio of 14.7 to 1 to burn completely. I do not recall what it is for a gasoline that contains a significant enough quantity of ethanol, but it will be different due to the change in quantity of carbons in the fuel. In either case though, a Lambda reading of 1.00 indicates a complete burn.

[Bitsyncmaster]

IIRC, a Lambda of 1.00 is a way of expressing a stoicheometric burn regardless of what fuel you are using. Gasoline (a mixture with variation, but fairy standard) has an air fuel ratio of 14.7 to 1 to burn completely. I do not recall what it is for a gasoline that contains a significant enough quantity of ethanol, but it will be different due to the change in quantity of carbons in the fuel. In either case though, a Lambda reading of 1.00 indicates a complete burn.

Your correct, the real mixture is changing so it's not 14.7 but the O2 sensor is still referencing the lambda reading and converting (if you have a wide band ECU) the reading to read 14.7

The narrow band sensor just swings on and off at lambda 1.00 so the lambda ECU is still holding the correct mixture for stoicheometric.

[SEO Motorsports]

To try and up the MPG I'll run the AFR in the low 15's under cruise.

[Josh]

Well im now sitting at 15.6 cruising @110kph, with 42 deg timing. Purring like a kitten! Previously tuned at 15.3, 35 deg @110kph and i was able to reduce most MAP values in the VE table by at least 5, some as much as 10! Excited to go on a trip and see what my fuel mileage is! Should be easily >30mph, currently averaging 29mpg highway now.

[Spittybug]

Well im now sitting at 15.6 cruising @110kph, with 42 deg timing. Purring like a kitten! Previously tuned at 15.3, 35 deg @110kph and i was able to reduce most MAP values in the VE table by at least 5, some as much as 10! Excited to go on a trip and see what my fuel mileage is! Should be easily >30mph, currently averaging 29mpg highway now.

Do you mean Kpa not kph? If so, why is it greater than 100 if you are normally aspirated? 15.6 is probably pretty reasonable in the cruise area, but cruise is typically ~2,000 Rpm to 3,000 rpm, with the load at ~ 40 or so Kpa. Timing wise, I would say ~13 for static, ~15 for centrifugal and ~15 for vacuum advance, so your 42 sounds about right.
What am I not understanding?

[Josh]

Do you mean Kpa not kph? If so, why is it greater than 100 if you are normally aspirated? 15.6 is probably pretty reasonable in the cruise area, but cruise is typically ~2,000 Rpm to 3,000 rpm, with the load at ~ 40 or so Kpa. Timing wise, I would say ~13 for static, ~15 for centrifugal and ~15 for vacuum advance, so your 42 sounds about right.
What am I not understanding?

Lol, no i mean kph (kilometers per hour)....

Load sits in the high 40s to low 50s when cruising.

I did notice my vacuum jump from 12 inches to 14 with the timing increase. Ill keep fiddling with the timing and see how high I can get it.


With regards to the delorean dizzy, I was reading Nick's book today. Sounds like they really stretched out the advance curve to squeeze every bit of mpg out of the 2.8. Im running EDIS ignition so I can change up the advance curve to my liking entirely thru tunerstudio. Very cool.

[Spittybug]

Too much advance will really hurt your engine, be careful. BTW, what does speed have to do with anything? It is RPM that matters along with engine load.

[Josh]

Too much advance will really hurt your engine, be careful. BTW, what does speed have to do with anything? It is RPM that matters along with engine load.

Yes I am aware. Keeping out a keen ear for pinging/knock / etc.

For tuning speed has everything to do with it. I want better mpg on the highway, where I set my cruise at 110kph. So I will see where the MAP is sitting at this speed, then tune that spot and work outwards. It is translated to an RPM for sure and thats how the MS sees it, but there is no RPM limit sign on the side of the road haha.

[Bitsyncmaster]

My 2005 Malibu shows MPG in real time. I'm pretty sure it just counts the injector pulses to get the gas consumption and applies that to formula with miles traveled. I would think someone has done this with these EFI systems you add on.

[Josh]

My 2005 Malibu shows MPG in real time. I'm pretty sure it just counts the injector pulses to get the gas consumption and applies that to formula with miles traveled. I would think someone has done this with these EFI systems you add on.

If you tap MS into a speed sensor it can calculate MPG. I had that same feature in my cobalt, it was pretty cool.