AFR's at idle
 

I'm curious on what everyone runs at idle? I've got it set to 12.3:1 and I think that might be a little rich...

Whatever idles the best if what you want.

Yes its really a matter of what the engine likes. Mine is most stable around 12.7

Should be able to go a little closer to 13, or even low 13's though.

This is why I don't like widebands...

If you read the FSM, it tells you to adjust everything possible until idle is highest.
The FSM does not mention anything about AFR's or widebands - you don't need it accord to what Mazda recommends.

A lot of things can affect wideband AFR's, and it's not going to be identical for all engines.
Most have reported that anywhere between 12.9 to 12.5 is about normal.
The engine just doesn't like idling any leaner than that - probably due to the fact that atomization is very poor at that low RPM's.

Bottom line...adjust AFR's until idle is highest; don't adjust idle trying to hit some target number.


-Ted

I was/am curious on what peoples idle AFR's are not to adjust my idle, but to figure out if I should consider the smoke I am seeing intermittently at idle could be caused by the AFR's I'm seeing.

Shouldn't be smoking at 12.

10, yes perhaps. But not idling at 12 or even high 11. What colour is the smoke? fuely smell?

mine is 13.2-13.4

Mine at idle is 11.5-11.3

That is due to the larger 750cc primaries and the stupid Power FC curse. For some reason you can't raise the AFR when you run larger primaries.

I idle at a solid 1015 rpm

Also a large street port

Mine idles between 10.6-11 and was about to make a post about it. It idles a little rough but drives fine, but to Reted, it doesn't seem to "like" where its idling. I've been using the idle adjust screw on the top of the TB, but its almost all the way in (can't raise idle an higher) and it still adles around 700rpm. I don't have a BAC, could adding on help any? What could manipulate mixture (so to speak) on an s5?

90 vert
stock t2
550s, 720 sec with Rtek 1.7
no emissions
throttle body mod
FMIC
*TPS is adjusted, though I haven't checked voltage range at ECU

I have found that it is more about your manifold vacuum than anything (Idle AFR).

It has been a little while since I did this, so I have tried to indicate the accuracy of the numbers listed.

Ignition Timing (BTDC) Manifold Pressure at Idle (kPA relative) Idle AFR
20 -75 to -80 12.2-12.7 *These are very close
15 -70 to -75 12.5-13.0 *These are also very close
10 -65 to -70 12.8-13.2 *More of an estimate on the AFR, vacuum is right
5 -60 to -65 13.0-13.5 *Pretty accurate (ran for a while at this)
0 -55 to -60 13.4-13.8 *Ran for a few minutes only
-5 -50 to -55 13.7-14.4 *Ran for weeks
-10 -45 to -50 14.4-15.0 *Was running at 14.8, closed loop until my fuel system gave up the ghost from the E85.

This was all with a 15 degree split.

edit: I have found that rotaries like a richer mix than piston engines at high vacuums (low absolute manifold pressures). I don't know why, but my guess is that the compression ratio is low and that the large surface area of the rotor face tends to draw the fuel out of solution.

The rotary actually likes a very similar mix to a piston engine at WOT, which largely discounts the surface area reasoning.

I found that cruising at 65 mph (-65 to -60 kPA) Manifold pressure, 2700 rpm) I needed to run absolutely no leaner than 14.8:1 in order to keep from misfiring. However at higher speeds (I won't state them here) when the engine is running at significantly higher load (say -35 to -30 kPA) I could run 18:1 all day without a misfire.

This actually resulted in my peak fuel economy being well in excess of the speed limit anywhere except for maybe Montana.

The engine speed had nothing to do with it, I could run at 18:1 at -20 kPA at 1,000 RPM without a misfire, but try to run at 18:1 at -50 kPA, forget it.

I am sure that this is not new news to a lot of you, I am just trying to make the parallel.

Piston engines do this too, but will run without a misfire at 14.8 up to about -70 kPA (although most of them have significant higher compression ratios than my rotary).

I am really looking forward to the high compression rotors, maybe I can run leaner at cruise... (wouldn't 40mpg be awesome?)

To ReTed's point, I have 460 cc/min injectors in mine, so I am likely getting better atomization at idle.

Actually, the longer durations may lead to better atomization and metering precision too.

Less vacuum gives longer time... I think you are on to a good theory, ReTed!

for WOT my engine seems to run best at about high 12s to the 13.3 mark. around the mid 11s and lower it sounds like its missing. My idle is around 12.2 to 12.7

Speaking on that atomization point, since I've changed to my new injectors (WAY better atomization across the board) I can idle my engine MUCH leaner. My spark also has something to do with it as well I'm sure.

Depends how much premix you're running. When I first started my car up this year I went with some Idemitsu pre-mix @ 1/2 oz/Gal (what they rec) and the OMP working as well. So basically I over oiled the engine for about 1/2 hour idle after sitting stationary for about 5 months. After I added some gas without premix, the smoke went away, AFR's didn't change much at all.

porting plays a HUGE role in that as well ;)

Please allow me to correct some misinformation here. These numbers were taken using my old AEM wideband.

A new, calibrated Haltech wideband is now indicating that my AFRs were not stoic as I originally thought.

The table above should actually read more like this:
Ignition Timing (BTDC) Manifold Pressure at Idle (kPA relative) Idle AFR
20 -70 to -75 12.4-12.6
15 -66 to -70 12.6-12.9
10 -62 to -66 12.9-13.1
5 -58 to -62 13.1-13.2
0 -53 to -58 13.2-13.3
-5 -49 to -53 13.4-13.6
-10 -45 to -49 13.8-14.0

I tried retarding the timing more, but the AFR had to actually go richer again as I went in that direction.

This is all taken at 700 RPM (my new idle). I was idling at about 1,000 rpm before, but I got tired of waiting for the trans to stop to use reverse.

Advancing the timing past 20 degrees didn't really increase the manifold vacuum any, nor did I see any changes in the AFR (went from 20 to 40 degrees with no noticeable change.
The engine will idle at stoic, but it misfired every 2 seconds or so (very annoying).

I apologize for the misinformation, it was correct to the best of my knowledge.

Correct you are!

I should list my porting - stock port timing (open/close), slightly cleaned up.

there is no target AFR for idle.

plain and simply adjust the idle until the idle starts to surge and then richen it up a tad. tap the throttle a few times to make sure the engine doesn't want to stall out when it sets down to idle, if it does richen it up a tad more.

that's all.. you don't even need a wideband to tune a car out of boost.

going based off of AFRs doesn't mean your wideband is even accurate, it may give you an idea if it is not however. most rotary engines will struggle to idle when going much leaner than 13.8:1 on my wideband.