Leanest AFR I can get away with?

[dieselbenz]

I think there is some FE to be gained here but not without spark control. At this point I'm using MS1 extra HR but ignition timing is being done by the stock mercedes EZL computer. The plan next summer is to add a 32 tooth wheel and ford EDIS. Until then I'm going to stick with 14.7 afr at low load.

[JanGeo]

Back in the old days (70's) the best A/F ratio for economy was 18:1 so you are close. Having run some pretty lean mixtures in my old 65 Rambler American flat head 6 with Polished heads and pistons and rather high compression (about 180psi) I found that when you lean it out enough you start to run less vacuum for the same speed and at highway speeds the coolent temps would start to rise a lot more than normal on warm days. Running water injection helps cool it a bit and having variable mixture control really helped a lot too. I was running a single SU carburator - single modified needle variable venturi carburator. Mileage was in the high 30's for a 6 passenger car in those days was very good.

[fowljesse]

Here, we have automatic water injection from the sky. Hooray?
In the future, I also want to do either the Ford EDIS, or a coil over plug from a Honda CBR Motorcycle. I'm also looking into Independant throttle bodies from a M/C. There is a guy who drag races with thre same engine as mine, and does 11's in the ? mile. I'm concerned about the torque curve, though.

[dieselbenz]

I don't know if it makes a difference but my engine has a relatively low 9:1 CR. That might be part of the reason why I actually INCREASED my fuel consumption by running leaner than 14.7. It definitely needed higher KPA (manifold pressure) to maintain the same speed and lost some throttle response but no FE gain for me. I'll try again later this summer.

[fowljesse]

Aha.
I have a 450SL that I was restoring before the economy took a dive. I never dreamed of getting good FE out of it.

[dieselbenz]

Mine is a 93 190e 2.3. The last of the Kjet cars. Even through I'm running the same 14.7 afr as Kjet did before, it still managed to improve FE by 10-20% depending on the driving condition. It did a 30mpg tank last week with the non lock up TC automatic transmission. I'm hoping to get it into the mid 30s once I install a 5 speed manual.
http://190rev.net/forums/showthread.php?t=35155
Don't get too hung up on lean burn. With MS and a wide band O2 you should be way ahead of the stock setup.

[DRW]

I've been using lean burn on my car. I found that the engine starts to misfire when it's too lean. Sometimes it's hard to tell when it's misfiring, so try running too lean, then richen it up about .5 AFR. I also learned that lean AF ratios have a slower burn rate, so you should add 1 to 3 degrees of timing to your maps in the same areas where it's most lean.

It's a good idea to gradually richen the AF ratio as more power is needed. AF ratio should be at it's leanest during steady light cruise. On my car I found that using less throttle than steady cruise caused some misfires, so my fuel maps get richer around 2-5% throttle. (I cruise around 7-9% throttle, for example).

I also found that opening the plug gap helped reduce misfires slightly.
FYI my car has 7.9:1 compression, stock.
HTH

[fowljesse]

I read your ecomodder link, tjts, and will check out the 190rev.

DRW, I got scared, and richened it up to about 16. I'm going to screw with it more when I get an exhaust temp sensor, and move the O2 sensor to the collector, since it's in 1 runner. It richens up immediately when there's lower pressure in the manifold.
Good news; I went through 2 tanks of gas (22 gallons) in about 3 days (677 miles). That's about 30mpg, which doesn't sound great, but considering it was about ? rush hour & downtown traffic, and ? having alot of fun in the twisty mountain roads, it's great! I would expect more than 35mpg FWY.

[dieselbenz]

Are you using a wide band O2? Bosch LSU with a 14point7.com controller has a built in EGT output from the O2 sensor.

[DRW]

Originally Posted by fowljesse

I read your ecomodder link, tjts, and will check out the 190rev.

DRW, I got scared, and richened it up to about 16. I'm going to screw with it more when I get an exhaust temp sensor, and move the O2 sensor to the collector, since it's in 1 runner. It richens up immediately when there's lower pressure in the manifold.
Good news; I went through 2 tanks of gas (22 gallons) in about 3 days (677 miles). That's about 30mpg, which doesn't sound great, but considering it was about ? rush hour & downtown traffic, and ? having alot of fun in the twisty mountain roads, it's great! I would expect more than 35mpg FWY.

Sounds like you're making good progress. Keep tweaking the settings while observing the car and it'll get better.

From my notes, 16:1 is the AF ratio with the highest EGT's. As you go leaner EGT's, NOx, knock propensity, and burn rate go down. Of course all cars are different, so what works for me might not work on your car, so be alert.