air fuel ratios? whats good/whats bad?

[Lucus]

Hey guys im just playing around with my 93RRC 4.6ltr V8 running a wolf 3d ver4 computer. I have a wide band 02 meter and have been playing around with the tune to try and get a little more power and a little better fuel consumption of it.

my high load/full throttle afrs are between 12.9 and 13.3 is this to rich for a fairly low comp (aporx 10.8 to1) na v8? what would be considered a safe range?

my cruising afrs (ie less than 50% load and 25% throttle) are between 14.5 and 16.2, is 16.2 toward the too lean end of the scale? i have heard of people going out to 17.5 or even 18 but i have also read that any leaner than approx 15.7 hurts fuel consumption as well?

The car has not cat fitted and runs a max of around 25deg of advance, whats peoples opinions on the good afrs for power and the best afrs for economy and long term eng life?

[cloughy]

10.8:1 low???? that's a fair wack of compression

anywhere down to 12.5 under WOT or fair leaning on it and up to 14.7 which is usually the goal for cruise, but I've never done fark all tuning, so take it with a grain of salt

[Philip A]

Your WOT depends on how you value power vs economy and your confidence about detonation.
You can run 14.7 if you have well tuned knock sensors.
BUT 12.5 or thereabouts will give maximum power and minimum danger of detonation.
Cruise is usually set at 14.7 "stoicometric" simply because narrow band sensors can measure it, and there are diminishing returns for leaner AFs.IE the fuel economy gains are small for each point of leaner AF.
14.7 is the point hwere all the fuel is burnt and thereis no excess oxygen.Just like a gas stove when the flame is blue vs when it goes yellow, =rich.

Many engines wil run well to 15.5 or 16 but lean "surge" and poor throttle response are usually the limitation. You can experiment with this to see what suits you as its unlikley to do damage. BUT often its difficult to transition to acceleration conditions and you may find flat spots etc.
Regards Philip A

[RangingRover]

my high load/full throttle afrs are between 12.9 and 13.3 is this to rich for a fairly low comp (aporx 10.8 to1) na v8? what would be considered a safe range?

That sounds pretty good to me, mine is set to 12.5 at WOT, but I think it could do with a bit leaner, and was thinking about heading back towards 13 to see how it goes. You are are in the right area, much more playing with it is probably going to be guesswork without a dyno. If anything I'd say you are possibly slightly too lean for maximum power, but then I haven't dyno tuned a rover V8, so its a guess. Check the megasquirt forums and see if you can find out somewhere what other people are running, there are quite a few running rover motors.

Cruise is usually set at 14.7 "stoicometric" simply because narrow band sensors can measure it, and there are diminishing returns for leaner AFs.IE the fuel economy gains are small for each point of leaner AF.

Not entirely true - most late model cars are more in the region of 15.5 to 16 under cruise. The key point however though, is that this AFR will not gain you anything unless your advance under cruise is also adjusted up to suit. On a car running standard earlier style injection (IE. 3.9/3.5 rover gear), it wouldn't make sense to shoot for this kind of cruise as it can't really differentiate between load and non load conditions, nor change advance curves. However, the OP is running a Wolf to control it, so the surging can be alleviated via an increase in spark advance (assuming he has ignition control) in the cruising areas, and the throttle response can be overcome by increasing the acceleration enrichment, allowing for a leaner target AFR.

On my car I'm running at 15-15.5 cruise with no surging or flat spots, but this hasn't gained me a lot of economy because I haven't had time to play with the advance curve to suit (and my wideband also crapped out). It is however, a litre or two better than 14.7 was. The map sensor based system also means as soon as throttle is cracked, or a hill is encountered, the ECU looks to a richer part of the map due to a higher pressure reading.

The car has not cat fitted and runs a max of around 25deg of advance, whats peoples opinions on the good afrs for power and the best afrs for economy and long term eng life?

25 deg sounds pretty good for that kind of compression, under a WOT condition. AFRS - see above. I would make a suggestion though to move to a slightly colder spark plug than standard if you are running lean cruise, especially if you do longer highway runs. I also wouldn't really suggest exceeding 16:1 AFR, its just a bit too far for my liking. And if you come across a good setting for economy, do share!