Is 15.5 to 16.5 AFR acceptable for Cruise?

[Pro Mouse]

Is 15.5 to 16.5 AFR acceptable for Light excelleration and Cruise?Do you Guys think this is To lean?

[EC_Tune]

LazMan found that on his GTO AFR's over 16.5 (I think it was 16.5 AFR anyway) started to lose MPG & definitely HP to maintain cruise. For the average car 15.5 is optimal for lean cruise. Keep in mind you have to add timing to make it effective.

[Pro Mouse]

EC,My Tuner has Timing is advanced a couple of degree's in these area's .How much timing would be needed?

[brianko]

EC,My Tuner has Timing is advanced a couple of degree's in these area's .How much timing would be needed?

Add timing until you no longer see a torque increase. That will be your peak cylinder pressure. Every engine is different. At low load/low RPM conditions, this might be quite a bit of timing.

[LazMan]

Thats about right EC .... the GTO did NOT even really like 16.5:1 AFR and did best around the 15.5 to 16.2ish range.

On my 07 Monte SS I can run a little leaner, 16.8 and no leaner, at the lightest throttles. I shift to .93 or there-about (15.6 AFR), which works well when in DOD, and feather it towards stoich as i increase the load, or when I get over 2400 RPM.

I can eek over 32mpg at 55-70 out of my SS with DOD on aggressively, a LOT of part-throttle timing, and staying out of PE (because I have it set PIG rich since I'm sure those pistons are HOT when I use that tune!)

I am not as familiar with GEN III cars, but I do know that if you want to do this on a GEN IV, your tune has to be SPOT ON all over the place with regards to MAF and SD tables/calculations, tuned with a wide-band sensor and in open loop so that the canister-purge effects arent taken into account while tuning. You then have to run open loop. I run just MAF when I do this so its less to tune.

If I remember correctly, on Gen III cars you can do closed-loop lean at certain airflows, which is far less complicated to implement.

Good luck, and let me know if you want me to post my fuel-economy tune from my SS.

-LazMan (not LAZY! ... LOL! Its short for Lazaro, my first name.)

[Gh0st]

I get best results out of my GTO with a 15.8 to 16.0. For some reason I can't command a 15.5 or 16.5. It's either 16.0 or 16.3. It's as if the values in the lean cruise table automatically round to the nearest value.

[Dragman]

EC when u say low load are we talking 45 kpa and down??

[colamotas]

Add timing until you no longer see a torque increase. That will be your peak cylinder pressure. Every engine is different. At low load/low RPM conditions, this might be quite a bit of timing.

Good info, but you would definatly have to do this on a dyno correct? I.e you propriceptive system wont be able to feel the difference!

[EC_Tune]

EC when u say low load are we talking 45 kpa and down??

Yes we're talking about below 50 Kpa and going leaner as the MAP drops.

LazMan -sorry for the goof above- fixed it...

[LazMan]

GhOst, it sounds like you're using the Holden Lean-Cruise tables. They rock, advance timing for you when you lean, and are a breeze to set up ... but unfortunately don't work on most vehicles.

I tend not to have the luxury of using them when I write an economy-tune. My GTO didnt like the leaner values, but it was the LS2 with 11:1 compression. I imagine the LS1's are more comprable with my LS4 (10:1 compression) and therefore can handle some leaner values.

On Gen IV engines like the LS2, LS4, etc, it takes much more work to do lean cruise. You have to give up closed-loop altogether, which really sucks.

EC, I lean from 50 down, but i tend to go less-lean at the 20Kpa column. More than slightly if the car has a big cam. Seems to keep the bucking away. ...and, on cars with DoD/AFM/whatever theyre calling it today, I run about 15.5 in the DoD range, except at the very end of it where I feather towards 14.7. Its a drivability compromise, but I have seen an increase in highway MPG of 20% on the 5.3 in the Monte Carlo (from 27 to 33).

I only run that tune when I'm commuting far and am not going to stomp on it. Ive tried writing all-around tunes, and do it well for other cars, but for my own I end up going all-MPG or all-performance. Its the mind of a tuner I suppose.

(ahh the old days where you could rig 2 chips and a switch between them...)

[5_Liter_Eater]

Laz, have you tried changing closed loop switchpoints now that we have the tables for it that work for LS2's in 2.22?

[LazMan]

I have played around with the new settings. My 'performance' tune uses lower switch points than stock. It kind-of works, but doesn't seem to work as advertised.

The O2 crossovers seem to be ignored and the computer uses 450.

However, my car had an "offset" of +50mv when it was warm. I've set it to zero, and even negative values. It seems the negative values are ignored. I also changed the rich/lean points from 675mv/300mv to 600mv/300mv.

If I log the MAF-LOW table versus O2 voltage, all the cells average around 450. Stock (i.e. +50mv) they would hover around about the 500mv range on average, so its a bit better.

My performance-oriented tune went from about 26mpg highway (stock) to about 29mpg if I don't stomp on it ... not bad. Still, my eco-tune breaks 33, but the driveability sucks.

The Gen III airflow trick for MPG doesn't seem to work for me. There is still a lot here we're not seeing. Take the 2007 Trailblazer SS ... it has O2 Rich / Lean points of 41mv ...complete nonsense, unless there's a multiplier or adder or some other stuff.

I wish we could LEAVE CLOSED LOOP at certain situations/speeds without going into PE. (My ECM only does 1.00 in PE, even if I set it lower.) There is no good all-around answer to be found here without a custom OS. Thank you EPA.

[Dragman]

(ahh the old days where you could rig 2 chips and a switch between them...)

Man wouldn't that be sweet if HP Tuners could do that!