This combination of gears and cam seems to be really happy cruising down the road at 16.5 -17:1 AF ratio. It seems to roll down the road effortlessly, with just the right exhaust tone, and excellent throttle response when you tip in a little more TB. Is there anything wrong with this? I know Stoich is 14.8, and this is probably not the cleanest cruise. But, is it the most fuel efficient? I have heard that GM has their fuel maps set for a very lean cruise. Any ideas or thoughts on this? Thanks for taking the time to think about, and discuss this.

_________________

Does your EFI use an oxygen sensor? Do you have closed loop feedback control of A/F?

Mitch

I'dbe happy with that for a no load cruise. If there is no knock and everything else reads OK...go with it.

I'm curious, what gear are you running and what kind of MPG are you getting Sam?

Stoich (14.7:1) is primarily for emissions, not mileage....

Around 16:1 give or take is the the best for mileage if there's no misfire.

So if it's running good, I'd leave it.

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Closed feedback is turned off for tuning. There are no misses, nor a hint of a flat spot. . The gear is 2.73. And so far I have been keeping it in 4th. The 5th gear has not been called for yet. I have barely gotten it above 2K in 4th. I have just driven it around locally on country/suburban roads: lots of hills, and changing from uphill load, to downhill no load at all, and high vacuum readings (low KPA).

I have a wide band gauge in the dash, and a narrow band O2 sensor for the ECU. The two seem to agree with each other. The wide band gauge reads 16-17:1 when the narrow band is putting out .1 volt. Acording to Emsvitil this makes sense. The wide band gauge was sort of goofy for awhile, but it seems to have straightened itself out. I think it had gotten somewhat fouled by the extra rich mixture I was trying to run before I recalibrated the fuel map, and just driving it for awhile seems to have brought it back to life.

If it runs this well when I get the entire fuel map worked out, I don;t see any reason to put the closed loop back in action. When it is pulling, the mixture is at 14.8, and my goal is to get all of the naturally aspirated cells to produce an AF ratio of 14.8 under medium load.

I am told 12.5:1 is a good target for forced induction, and I will tackle that after the rest is dialed in.

I don;t know what the fuel economy is yet. I have yet to fill the tank and drive it any distance. I am still driving around on last year's cheap gas.

Any more thoughts on AF target ratios. This is absolutely the most fun I have ever had with this car, and it is way more fun to drive than my 360 4 speed Dart was. It is finally to where the drivability is better than the carbureted system was. It was a rough year, but worth the effort.

Sam

_________________

Sam

Get you some new gas in that tank, you will never get it to quit pinging with year old fuel in it. It can even gauld cylinder wall. Even if the gas dont smell bad, it will cause you problems. Drain it if you can, if not atleast add new fuel to it & dont hold any tuning as being right until you get the old gas out.


Jess

Thanks Jess, I will do that today. It is pretty low, so I don;t think draining is needed. My understanding about old gas is that it is the volitile compounds that evaporate, and those are most responsible for starting, as they determine the initial flash point of the gas. I will do that though. It is good advice.
Sam

_________________

That's a lean enough reading I would wonder if the sensor is working correctly, but if it's working there, you might as well give the engine what it wants. If you have no drivability problems and no pinging, this will give you excellent gas mileage.

_________________
"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair