What effect, if any, does spark/timing have on AF ratio?
11-10-2007, 05:37 PM
#1
Jedi Master
Thread Starter
iTrader: (3)
Join Date: Apr 2007
Location: MN
Posts: 668
Likes: 0
Received 0 Likes
on
0 Posts
What effect, if any, does spark/timing have on AF ratio? I am about to order HP Tuners and I want to tune my secondary car(Cavalier) before my GTO so I can learn. In doing this, I will not be using a wideband so I will be holding off on all WOT tuning until I have a dyno available.
What is timing going to do to my AF? I have heard that I can tune almost every thing without a wideband except for WOT and I have also heard I need a wideband to do ANYTHING.
Can I have some clarification please?
What is timing going to do to my AF? I have heard that I can tune almost every thing without a wideband except for WOT and I have also heard I need a wideband to do ANYTHING.
Can I have some clarification please?
11-10-2007, 08:38 PM
#3
Timing will not affect air fuel ratio. You may see a difference air fuel ratio when measuring with a wideband as with less than optimal timing combustion efficiency can fall, the fuel will never dissociate and just passes thru, less o2 potential between in and out of the exhaust stream, and the wideband will read a touch off.
11-10-2007, 09:30 PM
#4
timing totally affects AFR; with not enough time for the flame to totally propagate, you'll have unburned fuel, causing a rich condition. it's quite easily visible, for example most automatic cars have quite a different timing in P/N vs D. sit there idling in P/N and then shift to D, and different timing will instantly change the resulting AFR.
11-11-2007, 01:59 AM
#7
TECH Apprentice
Join Date: Mar 2006
Posts: 326
Likes: 0
Received 0 Likes
on
0 Posts
Timing affects the thermodynamic efficiency of an engine to produce more horsepower, not the volumetric efficiency. Why would the a/f ratio change just because the engine is more efficient at converting heat energy to rotational energy? Now you might want to richen up your a/f a little if you bump the timing up too far to stave off detonation but the engine is not going to use that extra fuel its just going to end up in the exhaust and either way the o2 sensor (which looks at oxygen, not unburnt fuel) will see the same thing.
Trending Topics
11-11-2007, 06:35 AM
#9
timing totally affects AFR; with not enough time for the flame to totally propagate, you'll have unburned fuel, causing a rich condition. it's quite easily visible, for example most automatic cars have quite a different timing in P/N vs D. sit there idling in P/N and then shift to D, and different timing will instantly change the resulting AFR.
With an incomplete burn you end up with high levels of HC, and 02, but not high levels of CO, which by definition is a rich condition.
A/F ratio is just that. How much air to fuel is being ingested by the engine. What the engine does with that fuel, i.e., what you see on a WB or NB 02, is not a true definition of the A/F ratio. This is the main reason a WB reading cannot be trusted when monitoring idle A/F on a big cam motor.
You can have a WB reading of 17:1 at idle with a big cam, and have a rich condition.
Trust me, I use a 5 gas in conjunction with a WB, so I see it all the time.
11-11-2007, 07:49 AM
#10
Glad to see some critical thinkers.
AFR in is equal to AFR out regardless of timing.
Anyone want to argue with me about AFR changing before/after a cat at mixtures richer than 14.7?
AFR in is equal to AFR out regardless of timing.
Anyone want to argue with me about AFR changing before/after a cat at mixtures richer than 14.7?
11-11-2007, 11:23 AM
#12
9 Second Club
iTrader: (7)
Join Date: May 2005
Location: Cabot, AR
Posts: 3,126
Likes: 0
Received 0 Likes
on
0 Posts
Timing does not affect A/F ratio. And an incomplete burn is not a rich condition.
With an incomplete burn you end up with high levels of HC, and 02, but not high levels of CO, which by definition is a rich condition.
A/F ratio is just that. How much air to fuel is being ingested by the engine. What the engine does with that fuel, i.e., what you see on a WB or NB 02, is not a true definition of the A/F ratio. This is the main reason a WB reading cannot be trusted when monitoring idle A/F on a big cam motor.
You can have a WB reading of 17:1 at idle with a big cam, and have a rich condition.
Trust me, I use a 5 gas in conjunction with a WB, so I see it all the time.
With an incomplete burn you end up with high levels of HC, and 02, but not high levels of CO, which by definition is a rich condition.
A/F ratio is just that. How much air to fuel is being ingested by the engine. What the engine does with that fuel, i.e., what you see on a WB or NB 02, is not a true definition of the A/F ratio. This is the main reason a WB reading cannot be trusted when monitoring idle A/F on a big cam motor.
You can have a WB reading of 17:1 at idle with a big cam, and have a rich condition.
Trust me, I use a 5 gas in conjunction with a WB, so I see it all the time.
I agree mostly, as HC's are unburned fuel, but high HC's don't mean rich there's a rich condition, that means there is a lean condition causing an incomplete burn, leaving raw fuel in the exhaust. High CO #'s would be a rich condition. I played with a motor this last week with an EGA and validited what I posted above, and when I would set the CO's to a rich level like 10% the HC's were still low and uneffected, but when I leaned the CO's down to 1%-2% the HC went through the roof. I have seen cars at idle that "smell" rich and they are actually 15-16 afr, and when fattened up some, they idled a bit better and didn't smell any richer than before.
All that being said, I have personally gone from about 20-28* on engines before and it did not effect AFR, but I suppose if you went too far one way or the other past an "effecient" range for a motor then it may effect the WB readings due to in-complete combustion.
11-11-2007, 11:27 AM
#13
9 Second Club
iTrader: (7)
Join Date: May 2005
Location: Cabot, AR
Posts: 3,126
Likes: 0
Received 0 Likes
on
0 Posts
I had the luxury this week of being in Training in Atlanta/Kennesaw for Yamaha motor corp., and I got to use a Bridge Handheld all week long, comparing readings from the tailpipe vs. a fitting further upsteam in the exhaust and playing with CO watching the effects of HC while doing so. It was great, I am going to get one for the shop at work now probably.
11-11-2007, 12:50 PM
#14
I agree mostly, as HC's are unburned fuel, but high HC's don't mean rich there's a rich condition, that means there is a lean condition causing an incomplete burn, leaving raw fuel in the exhaust. High CO #'s would be a rich condition. I played with a motor this last week with an EGA and validited what I posted above, and when I would set the CO's to a rich level like 10% the HC's were still low and uneffected, but when I leaned the CO's down to 1%-2% the HC went through the roof. I have seen cars at idle that "smell" rich and they are actually 15-16 afr, and when fattened up some, they idled a bit better and didn't smell any richer than before.
All that being said, I have personally gone from about 20-28* on engines before and it did not effect AFR, but I suppose if you went too far one way or the other past an "effecient" range for a motor then it may effect the WB readings due to in-complete combustion.
All that being said, I have personally gone from about 20-28* on engines before and it did not effect AFR, but I suppose if you went too far one way or the other past an "effecient" range for a motor then it may effect the WB readings due to in-complete combustion.
A rich condition is any A/F numerically lower than 14.7:1 when discussing gasoline. HCs will go up in either a rich or lean condition. In an overly lean condition, HC will skyrocket. 02 levels will go up as well, due to the incomplete burn, but CO will remain low.
As for timing, too much or too little, causing incomplete burn, it may skew the WB readings, but that does not mean its causing a change in A/F ratio.
11-11-2007, 01:06 PM
#15
Jedi Master
Thread Starter
iTrader: (3)
Join Date: Apr 2007
Location: MN
Posts: 668
Likes: 0
Received 0 Likes
on
0 Posts
Ok it looks like we have determined that spark will not affect A/F until AFTER the burn which then it is completely irrelevant in terms of engine power correct?
11-11-2007, 01:14 PM
#16
I dont follow you. NONE of it is irrelevant in terms of making power. It all relates. Too much timing is detrimental. Too much fuel is wasted energy. Not enough timing is a waste. ALL of the conditions I've mentioned may result in different WB readings but it doesnt change the fact that timing has no affect on A/F ratio. Not WB readings, the actual amount of fuel the computer, or carb for that matter, is flowing thru the engine.
11-11-2007, 01:21 PM
#17
9 Second Club
iTrader: (7)
Join Date: May 2005
Location: Cabot, AR
Posts: 3,126
Likes: 0
Received 0 Likes
on
0 Posts
If you read my post more carefully, you'll notice I said 'high CO which by definition is rich'.
A rich condition is any A/F numerically lower than 14.7:1 when discussing gasoline. HCs will go up in either a rich or lean condition. In an overly lean condition, HC will skyrocket. 02 levels will go up as well, due to the incomplete burn, but CO will remain low.
As for timing, too much or too little, causing incomplete burn, it may skew the WB readings, but that does not mean its causing a change in A/F ratio.
A rich condition is any A/F numerically lower than 14.7:1 when discussing gasoline. HCs will go up in either a rich or lean condition. In an overly lean condition, HC will skyrocket. 02 levels will go up as well, due to the incomplete burn, but CO will remain low.
As for timing, too much or too little, causing incomplete burn, it may skew the WB readings, but that does not mean its causing a change in A/F ratio.
11-11-2007, 02:28 PM
#18
Now that 5 gas analyser could be more accurate since we know from chemistry what ratio of gasses for any given AFR will result. Since it looks at more than just free oxygen and the curves of the other gasses don't have the same shape as free oxygen a more plausible answer can be given. If the O2 is too high but the other gases are pointing in the oppisite direction then the machine can throw out the data from the O2%.
