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 Post subject: Timing/jetting Shrinker
 Post Posted: Thu May 05, 2011 5:38 am 
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Explain how jetting and timing work..

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 Post Posted: Thu May 05, 2011 8:52 am 
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I cant answer this question as a simple answer, its too interactive.
There are more factors than just timing and jetting. Jetting is not about the total AFR its about the fuels match to the engine. Fuel ignitability influences timing, Droplet size and distribution influences timing and AFR necessary for max power. Fuel’s HC constitution has little effect on timing as far as burning rate of the gases is concerned however the distillation temperature of the fuel has effect upon vaporization achieved at ignition point and subsequence effect upon pressure rise and subsequent effect upon gas emissions therefore the timing is altered in response to that.

Fuel ignitability--- The different HC’s in fuel require varying amounts of energy to reach ignition energy level. The energy level to ignite composite gasoline is very low somewhere in the order of 6 millijoules but that’s no good to anyone. A typical MSD has 160 to 180 millijoules of energy so it may seem to be way over the top, but theres a reason for it and its all tied up with jetting and timing. The flame kernel that gets formed at the minimum energy level required for combustion is very tiny, Turbulence exists in the arc gap and you can take advantage of that by having arcs with duration and more energy joules. Getting that right makes the flame kernel much larger and it reaches the limit of laminar flame size earlier. The upper limit of laminar flame size is 10mm diameter. Once the flame kernel gets to that size it cannot be extinguished by turbulence, in fact the more you throw at it the faster it grows, it’s a self feeding monster. However at the start its only tiny so once it’s grown up to 1mm size it can be affected by turbulence in the shape that it forms. If the flame kernel receives too much turbulence while its still in its laminar formation phase the flame kernel can be partly extinguished and the time needed for the cylinder to reach pressures that gasify the heavy HC’s is extended. So to combat that you have to advance the timing. Advancing the timing starts the flame kernel in conditions of less turbulence because the piston is further down the bore. So a more stable flame kernel growth is achieved BUT the pressure rise is working against the piston so pumping losses are increased. Then because your starting the flame earlier you need to make the mixture richer to avoid detonation. Sometimes I see this relationship on engines and I see them go nowhere no matter what timing you change etc and you can see the gases respond in the manner they should for advanced timing.

Droplet size--- The vaporization of fuel is dependent upon the energy level of the droplet and the pressure upon it. The energy level is the temperature of the droplet, if the droplet is cold it has to have a lower absolute pressure upon it in order to turn to gas than a hot droplet would. You have to factor into your thinking about this that the droplet has all the chemicals of the fuel in it and the low distillation temperature HC’s vaporize first leaving the droplet getting more and more concentration of the higher temperature chemicals. So imagine that the droplet is boiling away as it passes the intake valve but its not all gone, As you port your heads or run bigger valves you gain valve curtain area and you reduce the pressure loss in the curtain and port etc so you have higher pressure there and less vaporization of the droplet there. Now you have more high distillation chemicals entering the chamber still in liquid form. That’s why you have to increase compression pressure when you port the heads or go bigger cam etc, you have to get the energy from somewhere to gas the fuel so it has to come from compression heat in order to replace lost vaporization due to vacuum.
If you do experiments in carburetion by changing droplet size as I have done you’ll see that the gases and the consumption of oxygen is greatly affected by droplet size. You can engage all the oxygens in the early stages of the burn if the droplets are very fine but there is a down side to that and its CO control. If the droplets are very small the mixture has to be leaner and the accuracy of the systems of the engine have to be improved otherwise you generate too much CO and also run the risk of thermal runaway in the chamber because your so close to stoich and that’s dangerous for high power per cube engines. Chambers generating high CO in the initial phases of the burn are very sensitive to exhaust contamination. The exhaust system has to be spot on or you lose heaps of power.
If you cant get sufficient gasification of a mixture close to lambda .98 for instance, the temperature of the air on the day changes the gasification sensitivity and you go from full gas to part gas and totally different style of burn and risk factors. Its very tricky to get right so to compensate you run larger droplets and richer mixture. When I’ve run droplets to get full gasification I’ve managed to get engines to zero emissions level without cats even at WOT but the sensitivity of doing that is extreme. It too hard for commercialism. The fuel LPG can be run in gas form because its limited to one or two chemicals basically. But even it suffers great power loss on hot days. Liquid fuels have far greater usability zone.

Droplet size influences the gasification level achieved in the chamber so it alters the optimum ignition timing point. Depending upon the gasification achieved in areas like the valve curtain etc at different point of load and rev range and all the other factors depends the timing. When you experiment with this stuff you can easily detect power changes just by driving the car, of timing alterations of less than 1/10th of a degree. Its so sensitive that’s its not commercially viable. So we compensate by running larger droplets. To sum up the whole scene and put it simply there are not accurate enough systems on hot rodders cars to utilize the full benefits of droplet control.

Scientific research done on the subject of droplet influence is done all the time but there has only been one test done that in my opinion was correct enough to be reliable information and the results of that are that the fuel balance of HC’s has the most influence on the optimum droplet size of any factor. The objective is to not have complete gasification of gasoline. The reason for this is that the ignitability of the HC’s has a great influence on the reaction speed. Other reasons are also explained later.

Reaction rate--- The reaction of fuel is not the appearance of flame. Flame means nothing, Visible blue flame(as it is in the chamber) is just formaldehyde reacting and emitting light, the oxidation reaction of the molecules actually commences at temperatures as low as 125F. Its only some of them that start this low but nevertheless it’s started. There is a reaction happening before and behind the blue flame, however we tend to talk in terms of the flame. You get a faster reaction rate by not fully gassing all the HC’s. Droplets (very small molecule sized ones) in the presence of advancing flame create faster flame growth due to the richer environment that is present around the exterior of a droplet. (See the AFR section.) The variations in reaction rate per combustion event are immense (due to AFR distribution) and because it’s a varying random thing it’s better to average the result and the safety by running not fully gassed environments, hence we use droplet size to compensate for that. See how droplet size has many varied reasons. Now chuck that same carby on a BBC and it all falls out the window, all of a sudden your observing an engine with port swirls opposite on some cylinders, fuel slamming into bore walls on some cylinder etc, it’s a mess and how the hell can you optimize 4 cylinders when 4 others might be at risk? So you have to compromise the whole scene by using bigger drops than engines like a Chrysler Small block or a Ford Cleveland.

AFR--- The AFR that’s easiest to ignite is 10.5 to one. However this is not the optimum for power, that’s why we need more ignition power than a simple scientific test answer. Its important to always look at science results and apply them to the world you live in.
The leaner the AFR the slower is the reaction speed. So lean mixtures need more advance.
Having droplets still present as the reaction front is advancing increases burning speed. However the droplet size needed is critical and its variable depending upon the HC mix. The environment around a droplet is the richest possible at the time and as you extend a distance away from the droplet the AFR becomes less rich. The droplet size and its evaporation rate combined with the distribution of the droplets allows a certain environment of the spaces between droplets. If this space is 10.5 AFR then the reaction speed is increased. The flame will fold over upon itself in pockets and this increases the surface area of the flame and thus increases the energy field area thus increasing the mass fraction burn rate at any point in the cycle. Its this critical mass fraction burnt measurement that determines power. You need the right amount of fuel burnt at the right piston position to get the maximum power from whatever the engine design is (stroke rod ratio). So changing combustion chambers etc changes the need to droplet size and timing etc.

Ignition energy--- The energy from the arc forces the reaction velocity of the flame kernel to a high value during arc duration. The electricity holds the reaction rate at an unsustainable rate. Within 0.5ms of arc cessation the reaction rate drops to normal for the chemicals involved.
Reducing the contact area of the sparkplug with the flame kernel increases the flame kernel growth rate. Likewise locating the arc away from the cylinder head surface increases flame kernel growth rate, its very important to grow the flame kernel to stable size as fast as possible. Reducing the mass of the ground electrode increases flame kernel growth. That’s why there are plugs with tapered ground electrodes.

Complicated stuff. If your going to go into this then be prepared to go old and grey and still be baffled.


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 Post Posted: Thu May 05, 2011 4:00 pm 
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Location: COLORADO We got no air!!!!
Jet provides the quantity of fuel and the timing tells it when to start burning!! ;-)
or
What shrinker said!

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 Post Posted: Thu May 05, 2011 4:55 pm 
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Very Funny but the point I'm making is the size of the jet has nothing to do with it for some conditions. Take Kens predicament for instance, hes changed valve timing relative to the piston and changed inlet manifold and the burn changed. The compensation for that is to increase jet size dramatically just to achieve the same AFR in the exhaust. Its the chemistry of the burn that has changed, the droplets are now different size because of the different jetting and the quantity of fuel is more as well. The environment of the atmosphere in the chamber has been changed and the cylinder needs different HC mix to reach the same conclusion as before in the exhaust pipe. With a different fuel blend with equivalent stoichiometric value the jetting may come back to how it was before.
With Kens changes it made it go lean as read on the WB. With just WB data you have to guess a few things based on experience and the most likely scenario is that the changes made the burn less efficient and oxygen was being wasted. Thats backed up a bit by the loss of ET so you would assume that its less efficient by looking at both factors. So in response Ken has increased jetting up what, 6 or 8 sizes? Each size is around 4% more fuel so hes increased fuel quantity but its hard to know exactly because the metering block may be influencing the flow at those jet ranges more than the jet does itself. So ask yourself where is the extra fuel going? It goes better with the extra fuel so it needs that fuel for some problem thats happening inside the cylinder its not fuel being used to burn in the exhaust pipe its actually burning in the cylinder and improving power. Kens knows what hes doing so we trust his observations. So if its got lots more fuel in the chamber then why is it now necessary to do that? It's because the products of the combustion have been changed due to the changes of vaporization brought about from the cam advance and the manifold change. The products of combustion are the result of the energy level of the chamber at the time of the utilization of the Oxygen molecules. If you change the fresh air environment in the chamber it changes the speed of oxygen interaction. CO is the culprit, CO takes nearly as much energy to combust it as what it releases. That means that if you even slightly increase CO residual you change the fresh air side of the environment to a much different energy level required to start the combustion process. The CO gas present is surrounding fuel molecules and sucking energy so that it can burn first. This delays the burn of the HC mix of the fuel. The CO converts into CO2 and all of a sudden you have lots of fire extinguisher gas very early in the burn and you have used up lots of O2 in creating a low heat yield output. So you need to artificially change the mix by flooding the chamber with fuel and using the limited available energy to boil a greater number of low temp HC's so that you can engage some O2's in Hydrogen burning(and create water) because that's the most effective heat yield reaction. The excess fuel that cant be used because you have eventually run out of Oxygen's is blown out the pipe as unburnt HC's then reacted by the WB cell and displayed as rich enough to make you happy again. Its all junk, you need to see the gas percentages that are created, I understand that WB's are cheap and they help a lot but its wrong that the industry is promoting the idea that WB's read the true AFR and all you have to do is use them. You simply cant, proper tuning is done with gas benches, gas benches teach you so much more but it takes years of learning and experience to get there. Yes I know that's not what racers want but I still gotta say it. The industry is trying to dumb down the racer by telling them that all they need is Wide Bands. I hate it.


Last edited by shrinker on Thu May 05, 2011 7:14 pm, edited 1 time in total.

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 Post Posted: Thu May 05, 2011 7:12 pm 
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Berreta, I dont think your asking for simple run of the mill answer to how jet and timing interact, its pretty simple to say leaner needs more timing, or run it rich and retarded and its safe. Just what are you asking?
If you look at Kens experience or other people who have tried his carby on their engines and have done jetting changes then you can see that there is great variations in the amount of fuel needed to achieve a similar result in different engines as measured on an AFR guage. A venturi creates a depression the same for any CFM air flow and the jet delivers the same fuel relationship to it. Theres not much variation between one engine's suck and another, but there is great variation with what the cylinders do with it.
Thats because its not about AFR by jetting its about combustion products by vaporization and residual from the previous burn. Its how those products create cylinder pressure that can be converted to torque by the crank rod mechanism. Thats why this whole subject of the Infernal Combustion engine has been going on for over one hundred years now with major changes in efficiency occurring all the time. About the only engine that has no problems is the Jet engine. And look at how good they are, they can get close to 100% efficiency whereas the poor internal combustion piston system is pretty archaic in comparison. Obviously continuous combustion is the way to go.
When you have just a single HC like methanol its easy, all the molecules do the same thing at exactly the same energy condition, thats not the case for complex fuel mixtures like gasoline. What I said about CO is very important. Its the sequence of gas production and where the CO occurs that makes a great change in the result.The first step of the combustion is hydrogen creating water. 60% (approx) of the energy comes from that, so if you contaminate the air with CO you disrupt the most important stage. Its just like racing, sleep at the start line and you loose, you have to do tremendous work to beat the other guy down the track. It's the same with the combustion, you have to set the conditions up correct before the combustion starts.
The setting up ready for combustion starts right at the carby or injector etc. Then it gets stuffed around and altered or fixed or wrecked by the manifold or cam etc. So what were doing to the carby is something to correct a problem further downstream. Check out this story. I had a problem with one customers car that took a while to figure out. I looked down the carby barrel when it was on the chassis dyno and the fuel was being slammed against the wall of the barrel near the centerline of the carby. The butterfly didn't have to be opened far to do it, it even slammed the fuel at Wide open throttle. It was going over at an angle and running down the wall of the barrel near the center bolt area. So I put that carby onto another engine and the fuel didnt do that, it ran as per normal down the center of the barrel. So I put a spacer under the carby on this faulty engine, that reduced the effect a bit but it still did it. If I used something like a 2 foot spacer i might have had normality back in the barrel. Obviously not practical. The engine was troublesome in that its power varied all the time. Sometime it would make 245 kw then it lost throttle response and power. It didn't used to do this years ago with the fuel flow, and it hadn't been changed in any way other than wear over the 5 years. But somehow it had developed some effect in the plenum, possibly due to a change in cam wear and how the valve timing interacted with the fuel changes over the years here. I couldn't fault it with compression or tappets or leak-down or anything else we tried. I think it had slightly worn a lobe and slightly altered the valve timing on one or more cylinders and that had upset the air flow turbulence patterns in the plenum. Its likely there was some effect like a tornado happening and thats why the fuel was going to one side.l It was amazing. I could jet it up or down and time it anywhere and nothing stopped this effect, nothing fixed the consistency issue with the engine and nothing changed the power greatly either. I fixed the ignition and checked everything, now the engine is getting a rebuild.

Once upon a time i did a test on my work van with reducing the ignition energy and I ran a WB and a gas bench at the same time and posted the results in Innovates forum. Changing the ignition energy caused the WB to read a change in AFR whereas the gas bench wasn't fooled. Of course the AFR hadn't changed but the combustion efficiency had and that's the problem with WB sensors. They react to combustion efficiency and give inaccurate readings. Ken changed jets heaps and didnt get appropriate AFR change to the jetting, so something is not right. Somewhere something is inaccurate or changing.


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 Post Posted: Thu May 05, 2011 8:14 pm 
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I think what he was wanting to know was, since changing the timing affects the fuel the engine wants, and changing the jetting changes the timing the engine wants, what is the most efficient tuning procedure to arrive at the best, or close to best, timing and jetting for a particular engine combination? If you don't have gas bench. =;

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 Post Posted: Thu May 05, 2011 8:30 pm 
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Shrinker, If you remember I had some oil getting through the intake gaskets and that was making my WB 02 go a little wackey though the EGT's were telling us that there was no issue with it being lean..

Now with a new intake and everything sealed up good and this intake although it is that same part # it is ported different that
the other one. The plenum is bigger and the port match is perfect..

I also pulled out the 4.57 gear and put in a 4.29 gear and now it needed alot more jet with the same timing. Also it did run almost as fast in air that was not as good when it ran it's best...
Im up 3 jet sizes from last year and looks like it's going to need another one and more on the back as they are on the hot side..

Donee sums it up good...Good talking to you last night =; Get working on that car :-

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 Post Posted: Thu May 05, 2011 8:35 pm 
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The answer to that is use a gas bench. But the answer your seeking is probably get a knock sensor and make sure its not detonating and start that way. A CO meter is cheap and accurate but too slow for racing but a CO meter with a WB is a good budget combination that is hard to beat. It is useful for street tuning.
Changing the timing affects the fuel that has to be used to cover up the detonation from the timing. What I mean is you can use C14+ in a stocker and advance the hell out of but for what reason?-- just to brag at the Drinking Bar that you can run advance? All fuels have virtually the same heat energy in them, so it comes down to how much you can compress them. Its the way you manage compression that is important. The compression heats the gasses up and they can reach detonation so its what temperature you start compressing with that is important and you lower temperature by increasing vaporization. Vaporization reduces the temperature during compression thats what you want to do to compress it more than the other bloke and beat him.
But in the end the only way to run an engine on a dyno, and have some tools that can tell you if its got the best combustion efficiency is a gas bench combined with cylinder pressure measurement . Exhaust gas analysis by itself is the most useful single tool. It shows if your using the Oxygen's and how you your converting them and if your measuring the power and do combustion changes and drop power you can see why and then you can correct the design of the engine. That is how to develop engines.

beretta, if you have to cross jet then its all wrong. Your compensating for what I explained in the above posts. Get the cylinders working correctly and there is no need for cross jetting. If its getting hot then address the mixture control and water flow and droplets and exhaust pipe shaping and contamination. Dont bandaid stuff Correct it. There is only one perfect burn and you dont find it by creating variables like cross jetting. Spending effort to identify what is that causing you to have to need cross jetting is the thing to do.


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 Post Posted: Sat May 07, 2011 8:38 am 
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A different way to ask the question, using these assumptions. Each engine has a combustion peak pressure point (PPP) that makes it happy, you can leave the jetting alone and move the timing around and by watching the mph at the end of the track, zero in on that PPP. If you change the jetting you will need to move the timing to find that happy PPP again. So each jet selection has an optimum timing position based on the PPP, and each timing position has an optimum jet selection based on the PPP. But there is a small window of jetting and timing combinations that are going to optimum for your given engine combination. With our 02 sensors, EGTs and time slips what would be the most efficient process to zero in on this small window?

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 Post Posted: Sun May 08, 2011 1:19 am 
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Ahh I see, the problem with just that equipment is you dont truly know the combustion efficiency, but you can get an idea by using the EGT. You need to create an Excel program that cross references the EGT to the AFR. Or apparently that can be done in logworks with a math channel or something like that its called. never played around with that part of logworks myself yet.
If you increase combustion efficiency with a design change, for instance like adjusting to different tappet clearance, the EGT will go down at the same timing and AFR. Any time EGT goes down with same AFR then you have increased energy conversion to the crank. As the energy from the burn is converted to torque the temperature of the gases in the chamber is reduced, so lower EGT is more energy conversion provided its done at the same AFR. Is that answer your after?


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 Post Posted: Sun May 08, 2011 4:40 am 
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I should also point out this. Whatever AFR is needed by the engine to make the most power at any load percentage (measured as Manifold air pressure) of its maximum capability at any single point in the rev range, the same AFR is needed at every point in the rev range. Said another way, For any given load percentage a flat line AFR is whats required. Provided you dont have overly restrictive air supply to the manifold then the AFR needs to be constant. For most drag racers thats basically get a flat AFR at WOT all the way down the track.
If you make more power at Maximum torque RPM by running it richer than your maximum torque AFR at a higher RPM then your actually compensating for a fault. In all the proper scientific tests ever done on the relationship of AFR to power this relationship has been upheld. The faults occur in the turbulence of the port, thats the main place but there's others. So what this all means is if you need 12.2 AFR to max the torque at say 5000 RPM and then you need 13 AFR to get maximum torque up at 7000 RPM, then your actually varying the fueling so that you can achieve sufficient vaporization at 7000. Its the old Top-End lean out scenario. The tuning situation for having to do that is common and its mostly tied up with turbulence inducing fuel separation and large droplets. Varying ignition timing is not the fix correcting the valve duration and the air flow velocities is the fix.

To date the most powerful AFR is still the 12.8 rule, but only in correctly gassed environments. That AFR needs to be richer in some circumstances like the wrong fuel for the compression pressure or overly large carburetors or inlet runners etc, situations where your trying to cover up detonation or the fuel falls out of suspension due to lack of air speed. Not likely for most drag racers.

If the AFR turns out to be leaner then its likely that there are problems with sufficient heat to vaporize the fuel. that could be the wrong fuel again or it could be wrong timing. A situation that cant be detected by equipment but can be by a time slip is where the timing is not optimum so that the exhaust is hotter and the residual is used to supply heat for the next incoming charge. Thats where a gas bench is handy.


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 Post Posted: Sun May 08, 2011 9:29 am 
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Good read. Thanks for starting the thread and asking the question Barry. Thanks for taking the time and typing out all this information Shrinker. I'd say alot of guys are going to benefit from it. =D>

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 Post Posted: Tue Jan 17, 2012 5:59 pm 
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Thats the thread. I have observed that same issue with my van a few times now. As the dizzy cap deteriorates the carbon track it makes too much CO.
WB;s ARE NOT ACCURATE thats the plain and simple answer to the differences between them and truth. I and some others have done demonstrations many times on dynos etc where the carburetor has not been altered but a combustion condition has changed in a cylinder and the WB's have read a major change in AFR. The change is far outside the possibility of random delivery from the carby. A WB sensor is a catalytic converter, it has the same catalyst as an exhaust cat in your exhaust system. The catalyst reacts Hydrogen and Oxygen to water first, since that is the simplest reaction, then it reacts Carbon monoxide with Oxygen to create Carbon Dioxide, THEN and only THEN does it react random constructions of Hydrocarbons and break them down into Water(via the first reaction stage mentioned above) and CO2. Reacting a HC into water and CO2 takes much more energy than reacting free H's and CO's.

There is a limited amount of energy available for the WB cell to operate, it simply cant do everything required of it under some situations. If the burn is high in CO concentration the CO reaction will dominate the energy field and the electronics only senses the energy field changes so the display shows super rich. However the actuality of the gas composition may be high CO but very low HC. Remember that because thats not what you will find in a text book. Most people think that CO is a gas that you can measure the AFR from but thats not true. CO is a gas thats formed when the temperature is limited to below the temperature of CO2 formation. If we controlled the fuel reactions so that the minimum temperature needed to create CO2 was never obtained there would be no CO2 no matter how much Oxygen was available. The reason for a gas product is not a simple whether or not there is Oxygen present, its whether or not the temperature ( read energy level) for electron transfer or sharing can occur. Oxidation--(combustion) is actually electron sharing between a host Carbon or Hydrogen atom and an intruding Oxygen atom. The Oxygen atom intrudes into the host's space via the energy of a collision and if the energy level is enough an electron will change orbit and share it with the Oxygen's electrons. (thats a basic description of part of the theory of combustion) For the case of CO the energy needed to force electron sharing with the next level up in the chain of reactions (to form CO2) occurs at a defined temperature and will not occur even one tiny bit colder. Kinetic energy is the main energy supply of reactions, collisions convert the kinetic energy into heat and once the energy (heat, temperature etc all the same thing) is high enough the next stage of reaction occurs. Turbulence and also the act of increasing pressure are increases of the kinetic energy.

Back to the WB sensor, a catalyst facilitates a reaction to occur at a lower temperature than would be the energy level (temperature) without the presence of the catalyst. A catalyst is also not consumed as a necessary function of facilitating a reaction. In other words, catalysts dont wear out from performing their function, they may 'wear out' for other reasons but thats different. The catalyst area in a WB cell is very small and can only handle a certain amount of 'load'. If the cell is highly loaded with CO the Oxygen transfer rate will be faster per time unit than with the same number of HC elements in contact with the catalyst. Thats because its faster to react CO than a complex HC molecule. So the Oxidation of CO 'sucks' the membrane transfering the Oxygen into and out of the cell dry. For a rich mixture the electronics counts the Oxygen transfer rate into the cell needed to complete the reactants and reports high rates of transfer as Richer. Thus the WB cell is overly sensitive to CO.

When the ignition energy is poor the flame kernel starts poorly and the energy level of the chamber has a lower peak etc and more CO is formed. What is considered to be 'normal' combustion usually has a defined relationship (within bounds) of CO to CO2 and HC. If the burn is close to stoich but on the rich side the accuracy of the WB is good because a good burn will have very low CO% close to stoich. Kill the ignition energy or retard the spark too much and even a stoich burn will have high CO and the WB will read the mixture as richer than truth.
A gas bench on the other hand will read that poorly ignited stoich burn and show on the screen that there is CO present and there will be O2 present and you can see that all the oxygen is not being converted and the amount of unused O2 will be the missing CO2. You just dont see how much O2 is not being used with a WB sensor. Power is all about using the O2's .
So how the hell can you tune power if you dont actually know how much O2 there is thats not getting used?


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 Post Posted: Tue Jan 17, 2012 6:04 pm 
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Two things, what I've seen with timing is that when you get to the optimum point the AFR curve will be the smoothest. And when you changed the intake, you may have had a change in fuel distribution, and that can mess things up as well. Larger ports and larger plenum can slow everything down, and have less energy added to the fuel.


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 Post Posted: Tue Jan 17, 2012 6:23 pm 
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Mark is correct. If you run larger ports etc and do nothing different in the cylinder to enhance vaporization you go backwards. Its all about vaporization and homogenization. You cant have homogenization without vaporization. Liquids dont burn so we have to have a process to convert liquids to gases before we can homogenize the gases. Zero vaporization is zero homogenization but poor homogenization is not poor vaporization. Vaporization has to come first, then you have to homogenize the gas state fuel. Homogenization is best done in confined high speed turbulent places, think the port and valve curtain. If the port has poor flow over the short turn for instance and the fuel separates its the liquids that you see pooling up , the gasses are fine, there just charging on into the chamber. You have a short turn fuel separation issue because you didnt vaporize all of the fuel in the manifold. Thats what happens, thats why stockers have small ports. Thats why fuel distillation is important. Unleaded street fuels are not designed to gas in the port or to gas all the fuel anywhere else for that matter. Unleaded street fuels are to feed the catalytic converter some HC's so it can generate heat and operate. Thats why their distillation temps are so high.


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