Engine: A/F ratio

[Teambeav]

I installed a A/F wide band on my Avanti where the non working clock was. Really helps dial the carb in. I do have a question? If the car does ping, would it show up as a lean condition on the A/F gauge?

[karterfred88]

Might, might not, pinging (pre-detonation) occurs for more reasons than just A/F ratio. You might note a very quick spike up or down right after hearing it or may not. If you keep going with the ping long enough for the reading to stabilize (and maybe after damaging the pistons) it will probably show rich-as the gases are not fully burning correctly in the combustion chamber. But, since it doesn't always happen on every cylinder at once, you are getting an average on the meter of the 4 cylinders on that bank,and after the gases have had a chance to reignite any unburnt gas in the exhaust stream. Up to the point of ping the meter is a good way to help jet the carb, but a knock sensor would be helpful in determining if it's mixture, timing or deposits causing it. Neat toy though, let's you see all the changes happening as you go through the RPM range.

[gordr]

I don't think so, unless it was pinging because it was too lean. Pinging due to lugging with too much advance dialed in, or due to low-octane fuel, would not register as lean. Another concern I would have is just how quickly that meter responds to changes.

[Buzzard]

Gord, I've been in Truchu and have to ask the obvious. Can you get decent fuel there other than for farm application? I would assume it is loaded with ethanol. Also I see you name tag relates to weasels. Do you have any?
Cheers, Bill

[Teambeav]

Weasels?

Gord, I've been in Truchu and have to ask the obvious. Can you get decent fuel there other than for farm application? I would assume it is loaded with ethanol. Also I see you name tag relates to weasels. Do you have any?
Cheers, Bill

No Weasels. My last name is Beavin and always got called Beaver in school. I drag race for fun and TeamBeav is our name and I am know as The Beav. All gas around hear is 10% ethanol. I just use a little racing additive in my fuel.

[Bill A]

I guess the question is what type of A/F mixture meter you are using as there is a variety. An o2 sensor watches to see what the oxygen content is in the exhaust stream, a real cool device to say the least. there are a couple of things that might be helpful in this discussion, complete combustion in 1 firing cycle takes 2-5 milliseconds so it is real quick. The o2 sensor installed for engine control watches it full time and adjusts the fuel delivery accordingly based on the exhaust values after combustion but before any catalytic converter. A typical gauge we might see on the market usually has a slow sampling rate meaning the value you see can be from a while ago so it isn't a current value. I used a lab scope tapped into the sensor output to see what was happening. Stoichiometric " I'm sure i spelled it wrong" refers to the perfect ratio of ! where the hydrocarbon base in the fuel is completely burned and that is about 15/1 air to fuel. That is way too lean to be healthy for an engine so we use an o2 sensor to adjust the ratio as needed. 14l1 which is more commonly accepted is the target but it is still pretty lean. In a modern engine the computer trys to keep it as close as possible and adjust it richer as power is needed. Better for smog and fuel consumption. It wouldn't be unusual for your meter to say 14/1 during normal light throttle operation but if it were quick enough you would see how quickly it changes even with a carb. Thats all the power valves, metering rods and secondaries in action. The leaner an engine is the hotter the combustion temps are so lane can cause high enough temps to make an engine ping, knock, detonate. It all sounds the same and none of it is good for your engine. i know the company I worked with for ever experimented with a secondary ignition cycle towards the end of the combustion process to increase burn efficiency and reduce pollution but abandoned it after a couple of years as it didn't pan out. So if your gauge is quick enough it can tell you tons of stuff but it's more for keeping an eye on aftermarket systems and it's kind of cool to watch. An 02 sensor works by varying voltage to a control module, lower voltage indicates a rich condition and higher voltage id a lean condition the middle being 0.5v. Long story but for me its fun to remember and if you got something other than bored thats real cool.

[Studeous]

Stoichiometric Ratio is 14.7 to 1.
I like that $4 word and one more.
dichlorodifluoromethane, which is freon.

[Mike Van Veghten]

As has been said, and to put it simply, no, not necessarily.
Pinging can come from being lean, it can come from just being too far advanced, which will not show up on a A/F gauge.

One thing people may not understand, pinging/preignition can and does from too hot a spark plug. If your engine is running good, (ring seal, valve guide seal, tune-up), and you race or do a fair amount of faster (freeway) driving, a step or two colder spark plug is or can be a good thing, as it allows more timing to be used without affecting anything else. Just don't go too far as the plug may not stay clean.

Mike

[Bill A]

Well 14.7 is close to 15 and the stoic word. I ran a chassis dyno for years and always had apprentices working with me which helped me and them as well. Anyway I remember when a youngster brought his tool into my bays and during one of our first conversations he used the S word. i looked at his and said What? . I learned something new and at the time I was considered pretty good so that instance taught me that no matter how you think you know someone will always come and dust your britches. That individual ended up being one of the best I ever got to work with and owns his own very successful business. He was the foreman at one of the biggest dealers in So Cal for many years before he got his own shop. i know, more long stories.

[Teambeav]

I guess the question is what type of A/F mixture meter you are using as there is a variety. An o2 sensor watches to see what the oxygen content is in the exhaust stream, a real cool device to say the least. there are a couple of things that might be helpful in this discussion, complete combustion in 1 firing cycle takes 2-5 milliseconds so it is real quick. The o2 sensor installed for engine control watches it full time and adjusts the fuel delivery accordingly based on the exhaust values after combustion but before any catalytic converter. A typical gauge we might see on the market usually has a slow sampling rate meaning the value you see can be from a while ago so it isn't a current value. I used a lab scope tapped into the sensor output to see what was happening. Stoichiometric " I'm sure i spelled it wrong" refers to the perfect ratio of ! where the hydrocarbon base in the fuel is completely burned and that is about 15/1 air to fuel. That is way too lean to be healthy for an engine so we use an o2 sensor to adjust the ratio as needed. 14l1 which is more commonly accepted is the target but it is still pretty lean. In a modern engine the computer trys to keep it as close as possible and adjust it richer as power is needed. Better for smog and fuel consumption. It wouldn't be unusual for your meter to say 14/1 during normal light throttle operation but if it were quick enough you would see how quickly it changes even with a carb. Thats all the power valves, metering rods and secondaries in action. The leaner an engine is the hotter the combustion temps are so lane can cause high enough temps to make an engine ping, knock, detonate. It all sounds the same and none of it is good for your engine. i know the company I worked with for ever experimented with a secondary ignition cycle towards the end of the combustion process to increase burn efficiency and reduce pollution but abandoned it after a couple of years as it didn't pan out. So if your gauge is quick enough it can tell you tons of stuff but it's more for keeping an eye on aftermarket systems and it's kind of cool to watch. An 02 sensor works by varying voltage to a control module, lower voltage indicates a rich condition and higher voltage id a lean condition the middle being 0.5v. Long story but for me its fun to remember and if you got something other than bored thats real cool.

Thanks Bill for your comments. I use a wide band that is very fast with a sweep and digital read out. I use one on my 72 Duster drag car to set performance at the top end of the 1/4 at 6200 RPM. On my Avanti I installed in the cross over pipe to get an over all reading. Found the car way fat and now have a 97 jet and a 71/44 metering rod for the primary's. Can set the idle at 12/13 to 1 AF easily but still goes rich off idol so next step is 75/43 rods. Rear jet is a 90 and still fat at wot. More adjustments to make. Having fun!!!!!!!!

[Bill A]

Sounds like you've got a handle on it. Step by step and you will refine it as you go. I agree it is fun to develop an understanding because it's like hitting the light switch and from there you can't sleep because this crap hits you at 1:30 in the evening. I have gotten out of bed and wrote myself a note so I wouldn't forget my dream. I did this stuff for 11 years straight, 8hrs a day and never once got bored. I discovered that altering the timing curve can effect AF ratios and get you a bit closer, but this was during the era of distributor machines and all that old time rock and roll. Then if your real careless start reading about flame propagation and and the effects of chamber shapes and for gods sake don't start reading about rod ratios. I ended up on a USAC open wheel pit crew for several years and the stuff guys know there is amazing.

[PackardV8]

Agree completely. Since today's pump gas doesn't give reliable plug readings, trying to tune a carb without a wide-band O2 sensor is looking in a dark room for a black cat which might not be there; and that's just at WOT. Simply not possible to get one right at all partial load and partial throttle without a wide band.

I installed one on the Packard Caribbean 2 x 4 in my Stude pickup and it has been a real education as to why the 2 x 4 has always been difficult to keep in tune. The root cause is if the four pairs of throttle blades don't return to exactly the same position, the idle goes wonky. That's why Rochester built special carbs with only one of the two having an idle circuit and accelerator pump. Even then, with two professionally rebuilt carbs, it's never exactly right.

One interesting observation is even using a direct throttle linkage, the cruise A/F is dead on 15:1 and hasn't required any adjustment.

jack vines

[Bill A]

You are exactly correct on everything. I did this stuff during the time of multiple carbs on German cars and the throttle plats adjustments are so vary important as well as off throttle. i had to sync them both at idle and at initial lift and that sir can be a dance. And for idle circuits, they did it with 1 in 2 carbs and one in each carb, the chokes were an issue with fast idle and yada yada yada. But you know what, it kept me busier than a 1 legged man doing what ever your story includes.. That was also the last of the mechanical rule injection, like the stuff used in the fighter planes and that was actually my specialty, they were so complex they were always a challenge. I loved them all the time I wasn't cussing them. And if it were me I would run a sensor in both exhaust sides, weird things happen and i know they are available and besides how cool is it to watch all those instruments that really have little effect on the outcome of your day.

[gordr]

As far as I know, all the fuel in Trochu is ethanol-polluted. Yes, I have a Weasel. BTW, I think we were in high school together, you were a year ahead of me.