Ferocity02

iTrader: (60)

What are you cammed guys running for idle timing? I know it varies from setup to setup but I'm just looking for a flavor of what's common. I've read that the ideal idle timing is where you make max vacuum, minus a few degrees so the over/underspeed timing correction can work it's magic.

I have a 212/212 114LSA 5 deg advance idling at 700 RPM. With the stock 18 deg timing it misfires a bit at idle, enough to set a P0300 after a couple minutes. I tried adding 10 deg and it didn't help. Then I retarded 10 deg and the misfires mostly went away, and it was able to hold the commanded idle a little better. <10 deg of timing at idle seems very low from what I've seen.

Thanks!

sweet-94z28

iTrader: (30)

I have a 228r and it likes 22-24 or so. Your cam really should not mind 16-20 or so. It varies greatly though. My stock GTO I had at 22 degrees of idle timing and it was fine. I usually just shut off P0300 in cammed cars. Just the chop at idle sometimes is enough to set it off. I know I have cracked open bolt on tunes and they do not have P0300 on in them.

AKHeathen

i modified the misfire threshold a little to kill the p0300 code, and it hasn't given me a problem since. i don't remember where i read the tutorial/walk-through on cam tuning, but the guy obviously was referring to rather large cams, not really ideal street use. some things i wouldn't really accept, like the real high idle, but the ve table adjustments made a lot of sense, and did help heaps. i have a similar cam (xr2 212/218 114) and it used to be a bear to tune when i started. after the fall, i had it idling back down at 550 without a mess of surging. it's just bugged me watching it run super rich, no matter what i did with all the adjustments. so, i finally got back into tweaking it. lowe and behold, i happened across the injector pulse width settings. that actually made a big difference in mixture, allowing it to correct as much as it wanted. it was set to .773ms across the board, so i started at 1200, and sloped down in steps of .1ms.... (1200=.665, 800=.55, 400=.45, 0=.35) i also read that, on the timing, that your 0rpm cells should be bumped higher, like +10degrees over 400rpm, or more, so it can better recover in a low rmp surge drop, and not die out. hope this helps. oh, btw, my main ve table was modified about -15% t 800rpm and about -30% at 400rpm cells. i plan on going back over those, too.

wait4me

iTrader: (10)

You used 4.1" ls9 gasket on your 3.7" block????


As for timing, That cam liked 16 degrees the most when installed straight up.

You have to add 45% to the low misfire table values to clear them up.

Also, with the fuel, change the table to enabled that allows for open loop fuel air adjustment. "Table B4206" Then fill in valid air fuel ratios for what you want to be commanding per temps "B3605 is the table number".

I usually command stoich everywhere in normal driving areas, if you change the value to non stoich, it will not go into closed loop, so you can fine tune the problem areas where it wants more or less fuel. I usually richen the cam up just a little bit to a 13.8 air fuel actual. It seems to make them idle smoother with less rpm jumps between events.

Ferocity02

iTrader: (60)

Good info, thanks! I'm attempting to do some VE tuning now. The first run of values are much lower than stock, about 18% lower at idle. Hopefully that helps a bit. I think mine is actually misfiring at idle, hence the high HC and exhaust smelling like fuel.

Thanks also! Many people are using the LS9 gaskets on the 5.3L and 4.8L blocks. foose04 put like 900hp through his on a 4.8L.

Are you suggesting I run open loop at idle? Sorry for my noobness, still very new to tuning. I'm trying to fix idle only without a wideband to get it to pass smog, then the setup will change completely, including the tune.

Ferocity02

iTrader: (60)

I used DVT in EFILive to adjust timing at idle real time. My base timing at the moment is 22 deg, and I went up to 38 deg. I got more vacuum the more timing I added, but it mostly stopped increasing at 36 deg. It went from 40kPa to 37 kPa. The idle quality seemed fine all the way up to 38 deg, but it did seem to have a harder time maintaining idle at higher timing. Volumetric efficiency drops steadily when timing is added from 1.2 g*K/kPa to 1.12 g*K/kPa.

So the question is, what timing do I go with?

Ferocity02

iTrader: (60)

Anyone else care to comment on their idle timing? Right now I'm leaning towards 28 deg. It seems to idle okay at this with increased vacuum and less air flow.

Slowhawk

iTrader: (12)

Thats a small cam. 20-24 tops.

Ferocity02

iTrader: (60)

What is the downside to too much timing?

flame

iTrader: (13)

Too much and you get a lot of Nox emissions

Ferocity02

iTrader: (60)

Is NOx a problem other than for emissions?

bwolfZ28

iTrader: (40)

My old NA setup was a 234/239 cam and I had it at 23-24 degrees.