Rhedalert

iTrader: (21)

I have HPTuners for my Camaro, and DHP Powertuner for my Olds. Now since my Olds is my "commuter car", I've been looking for ways to get the fuel economy up from its average of 22.5mpg (for winter. Summer driving is about 23.5). I've tried several different alterations from physical changes to PCM changes.


Most recently I played with timing advancement for cruise RPM. Stock is in the high 30's, low 40's for constant cruise speeds. I have increased all across this area to about 46 degrees. I feathered in the changes, but between 1600-2800rpm and 160-320 mg/cyl has the increases (peak increase at 240 and 280mg/cyl where most constant cruising on flat roads take place). As a result I managed to pull over 24mpg during my last few tanks. It may sound like little, but this car is so consistent on MPG, yet resistant to improve. To have a jump like this is rare. The weather and my route to work hasn't changed. I may try to push this further than 46 but not much. I get absolutely no KR.

Has anyone tried messing messing with an LS1 like this, or has anyone tried this with good results? How high have you gone? I don't want to start messing with cutting back on fuel *yet* (like I've seen when I searched) since I have both of my car's fuel trims near perfect. However, I would like to start testing with timing on the Camaro.

What does advancing timing at idle achieve? The cam I have in my DD gave a rough idle so I increased it to about 850 rpm to smooth it out.

Thanks for any advice or testimony.

turbolx

On a completely stock car, timing is intentionally retarded from MBT at idle. This is what allows the PCM to advance/retard timing to control engine speed and prevent stalls or overshoots at idle. If you simply ran MBT timing, the PCM would no longer have the ability to make quick corrections when engine speed drops due to gear engagement or addition of loads like A/C, P/S, and alternator.

Your larger cam probably has more natural EGR at idle, so the MBT point is also probably higher than stock. So even if you advance a few degrees from stock at idle, you should still have some cushion for torque reserve in there.

Rhedalert

iTrader: (21)

That's true, my cam is not too high in lift but has a lot of duration. Valve overlap is an additional 13 degrees over stock at 45 degrees which I'm sure contributes to the unstable idle at low rpm.

Last night I increased idle timing about 3 degrees and I dropped rpm from 850 to 750 (warm, in gear) and it seems to be stable so far.

Rhedalert

iTrader: (21)

Update: In the last few days I have increased timing in small increments, and I'm now running about 46-47 degrees advance while highway-cruising (no accel) The whole timing table has already been advanced about 4 degrees from previous changes. So the cruise cells are somewhere in the 7-9 degrees advanced from stock. She definitely feels spunkier, and I'll report back if the MPG's increased any.

dmart

iTrader: (3)

Does it run warmer with so much advance? I didn't know you could go over 45 ;]

Rhedalert

iTrader: (21)

nothing I've noticed. It probably wouldn't show up anyway being I'd have to be going at least 50mph to hit these timing cells. I'll check my scans though just to be sure.

2002_Z28_Six_Speed

iTrader: (19)

Yea. Well, when he starts to lean the AFR out the timing can be pushed further.

I run 40 all day long with light highway load and 15.3 against 1 AFR. That is the secret to good MPG.

I have heard of a time or two people running 16.5 or 17 against 1 but I would knife edge the table so you snap back rich again whenever any load is present.

I seemed to get knock when I was running leaner than 15.3 against 1 and then went into the throttle.

dmart

iTrader: (3)

So you are running OL? Wish lean cruise was enabled in the states ;[

Rhedalert

iTrader: (21)

Yeah I was just going to ask about that. This would ultimately be my next step (lean cruise style) What did you change to allow that to happen? I saw something on the HPT board under "MPG Tuning Ideas" but I think others had some flaws using that method.

2002_Z28_Six_Speed

iTrader: (19)

I think HPT has the same deal but with EFI Live I used the custom OP system that has a table by



MAP
x x x x x x x x x
R x x x x x x x x x
P x x x x x x x x x
M x x x x x x x x x

And it lets you name the new AFR by the current cell.

So I know the lighter the load the leaner I could go in that cell. But yes. Lean Highway mode is better.

Rhedalert

iTrader: (21)

I don't recall seeing that table but I'll do some searching.

I noticed also my fuel trims kept pulling fuel back since these timing changes... it hovered around -11 when coasting/throttle closed and -7 when cruising. I scaled back the MAF curve in these areas and it's back in tune, about -2 to 0. I also filled up last night and banked 22.8 mpg! Previously had been struggling to maintain 20. I drive 80% highway doing an average of 70-75mph.

2002_Z28_Six_Speed

iTrader: (19)

Cool. Try driving 60 MPH. People will hate you for it but it would be fun to know how it will affect the fuel mileage.

98Z28CobraKiller

iTrader: (17)

I dont believe that HPTuners has this table. Just to make sure I understand correctly. Are you saying that it looks like the Volumetric Efficiency (VE) Table but it allows you to populate it with differen't commanded AFR's?

Rhedalert

iTrader: (21)

I'll try, but I'll be driving my DD next week so it may be a while before I can experiment again. I could probably do 65mph safely, 60 I'll get run down



That would be sweet if we had access to a table like that with HP Tuners.

onecamaro1

Hp tuners does have a table like that, it for open loop though. Its the EQ ratio table. Its coolant temp vs map.

2002_Z28_Six_Speed

iTrader: (19)

That is a stock cal table. All OS should have that.

The EFI Live table is nice because it replaces PE and makes it easier to tune.

You don't have to turn PE on and off.

I know with EFI live you can do semi closed loop mode. Basically, any where you want to run closed you put in stoich on the MAP vs RPM table. If you want to run leaner or richer it will come out of closed loop.