how much is timing playing on afr?? - SRT Forums

moreause · 04-30-2009, 05:08 PM

last summer i was running on the safe side at around 10.5 afr
with modified timing

during the winter i just putted the timing to stock and afr was not that bad

but with hoter temp i'm falling to aroun 9.8 to 9.5 afr with no good result

just asking will put back previous timing anyway to see

Nick Chestnut · 04-30-2009, 05:24 PM

Quote: Originally Posted by moreause

last summer i was running on the safe side at around 10.5 afr
with modified timing

during the winter i just putted the timing to stock and afr was not that bad

but with hoter temp i'm falling to aroun 9.8 to 9.5 afr with no good result

just asking will put back previous timing anyway to see

Sorry dude... I'm confused. What are you asking?

moreause · 04-30-2009, 05:31 PM

does changing timing affect wot afr

is this better

**Mana4real** · 04-30-2009, 08:14 PM

Quote: Originally Posted by moreause

does changing timing affect wot afr

is this better

In short, yes it will...

SRT-What? · 04-30-2009, 08:43 PM

I haven't seen a big difference on my side. A couple of points, but nothing to bring you back to 11.5

moreause · 04-30-2009, 09:09 PM

i will check a bit else were i uped the afr but the car is still stumbling

time for new plugs

SebringLX · 05-01-2009, 08:40 AM

Yes, more timing = burns more fuel = runs leaner.

quicktalon11s · 05-02-2009, 09:43 PM

Quote: Originally Posted by SebringLX

Yes, more timing = burns more fuel = runs leaner.

i advanced my timing around 6 degrees and my afr's did not change at ALL. logic above seems flawed to me. more timing doesn't burn more fuel. it changes when the spark happens which changes overall cylinder pressure. fire the spark earlier (advanced), the more cyl. pressure you have. fire the spark later (retarded) the spark fires later reducing cyl. pressure. the amount of fuel going in is controlled by the injectors. you won't run leaner by changing when you fire the spark. you could run leaner because of things that affect the a/f mixture. like injectors, vacuum leaks/boost leaks etc.

oh btw sebring, i live in elgin and have a spare set of stage 2 mopar injectors you could try out for a bit to see if you DW injectors are the problem. i have fic 900's on the car right now.

moreause · 05-02-2009, 11:34 PM

from what i heard
if you advance timing and it's beneficial (more power)
if more power you have 2 choice.

1-you used the same mixture but transfered more power to the crank
2-you used the same mixture but you burn it better (more power) resulting in a leaner afr

JANNETTYRACING · 05-06-2009, 07:35 AM

I have seen instances where advancing the timing does lean the AFR, but that because I start with Low timing and work up.

So if timing is retarded it can show up as a rich mixture but not more than about .5 AFR.

Misfires show up as lean, exhaust leaks show up as rich.

harvboi05 · 05-06-2009, 09:10 AM

Quote: Originally Posted by quicktalon11s

i advanced my timing around 6 degrees and my afr's did not change at ALL. logic above seems flawed to me. more timing doesn't burn more fuel. it changes when the spark happens which changes overall cylinder pressure. fire the spark earlier (advanced), the more cyl. pressure you have. fire the spark later (retarded) the spark fires later reducing cyl. pressure. the amount of fuel going in is controlled by the injectors. you won't run leaner by changing when you fire the spark. you could run leaner because of things that affect the a/f mixture. like injectors, vacuum leaks/boost leaks etc.

if the plug is fired late a smaller percentage of the total injected fuel is burned and the rest of the unburned HCs comes out in the exhaust and is read as "rich" by the 02.

if the plug is fired early, a larger percentage of the total injected fuel is burned and less unburned HC are read in by the 02, making the exhaust sample "leaner."

there is a more complete combustion cycle, aka burn more of the injected fuel with optimum timing, affecting the AFR.