Target AF ratio for drivability

[Razor]

What do you have your target AF ratio setup at for drivability? Like idle and cruising?

 

[norbs]

13.5 at idle and 14.7 for cruising, 12.5 for low boost levels under 10 psi

 

[bruce]

Originally posted by Razor
What do you have your target AF ratio setup at for drivability? Like idle and cruising?

~14.2 ish.

WB verified.

 

[norbs]

If the car runs at 14.2, mine wont.........will stall

 

[Razor]

Thanks Norbs and Bruce.

 

[Otto J]

I target mine around 13 .5 to 1,If i run it any leaner than that,engine temps creep up a bit out of my comfortable range(160-180) if i run it much leaner temp rise into the 190s on a HOT day while cruising
But on a cool day its fine in the 14s

 

[Razor]

I'm having a tip in issue once in a while... while driving at 40 MPH 2000 rpms.. let go of pedal.. car slows down a little.. rpms drop to about 1000.. then when I give it a little throttle.. it gets a flat spot then clears up. Wont do it in idle.

Feels like the ol tip in issue with the 009's from a stop.

Rpms dont bounce so the throttle follower is working.

Also any issues with carbon buildup in cylinders with lower AFR's

 

[TurboTR]

If you run richer than stoich at light loads, yes you can certainly make things sooty.

One reason plugs stay so clean, so long these days is that the oem control system does a great job of maintaining stoich a/f ratio...

The target we'd like to achieve at idle is ~ stoich. If your engine runs fine there, leave it. One thing though, the sensor(s) can indicate stoich, no problem, but actually be say, half a ratio off. It seems that some have found a slightly richer setting at idle (13.5-13.8 or so) to work best with the FAST. But once you are away from idle you should be able to target and run at ~ stoich for light load cruising.

Razor your stumble issue after coasting is fixable.

TurboTR

 

[bruce]

Originally posted by Razor
What do you have your target AF ratio setup at for drivability? Like idle and cruising?

Just a reminder, but the leaner you go the more advance you have to run. Lean mixtures are slow burning.

Also, even a WB can be fooled a little by timing. ie running more then you really need, means adding fuel.

I run like ~24d at idle, and no more 38 in cruise. Running like 46 or so in a lean cruise condition, means putting alot of heat into the dome of the piston, and oil. You can wind up with tip-in preignition, and tip-in detonation when implimenting a lean cruise.

 

[Razor]

Re: Re: Target AF ratio for drivability

Originally posted by bruce
Just a reminder, but the leaner you go the more advance you have to run. Lean mixtures are slow burning.

Also, even a WB can be fooled a little by timing. ie running more then you really need, means adding fuel.

I run like ~24d at idle, and no more 38 in cruise. Running like 46 or so in a lean cruise condition, means putting alot of heat into the dome of the piston, and oil. You can wind up with tip-in preignition, and tip-in detonation when implimenting a lean cruise.

Bruce.. your input is invaluable as always.. Thanks.

I'll see where the timing is at in respect to AFR in the chart and adjust accordingly.

So is there a time to have spark advance in the 50+ degree range? Or have timing no higher than lets say 38 in cruise or otherwise. Maybe I need to look at some spark tables from some of my favorite chips and see whats going on there.

Thanks..

 

[bruce]

Re: Re: Re: Target AF ratio for drivability

Originally posted by Razor
Bruce.. your input is invaluable as always.. Thanks.

I'll see where the timing is at in respect to AFR in the chart and adjust accordingly.

So is there a time to have spark advance in the 50+ degree range? Or have timing no higher than lets say 38 in cruise or otherwise. Maybe I need to look at some spark tables from some of my favorite chips and see whats going on there.

Thanks..

Your welcome.

I've not seen any gains over 42d, maybe in an EGR application you'd need that much. The GN chamber design is dang good so it, doesn't demand as much timing as other brands.

Lots of *chips* use a timing table that's only slightly different then stock. With most or only changes in the higher LV8 areas.

 

[norbs]

You can run upto 15.3 for crusing, the 14.7 is only used to keep nox emissions down to lower levels and to keep the catalytic happy. The engine will be most efficient at 15.3