---------------------------------------------------------- Engines-List Digest Archive --- Total Messages Posted Fri 05/28/04: 4 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 07:01 AM - Re: air/fuel ratios (Gary Casey) 2. 07:06 AM - Re: Re: Engines-List Digest: 8 Msgs - 05/26/04 (flyv35b) 3. 12:18 PM - Re: lean vs rich (B.P.) 4. 02:07 PM - Re: Re: air/fuel ratios (Gordon and Marge) ________________________________ Message 1 _____________________________________ Time: 07:01:37 AM PST US From: "Gary Casey" Subject: Engines-List: RE: air/fuel ratios --> Engines-List message posted by: "Gary Casey" <> I'm not an expert either, but I'll take a shot. First, I'm not sure I'm not sure what is meant by "efficient" combustion: You could talk in terms of percent completion and in that vein combustion in a cylinder is generally very complete except for very rich or very lean mixtures. On the rich side of stoichiometric (the chemically correct air/fuel ratio) the percent oxygen in the exhaust will be low enough (probably less than 1 percent) for us to say the combustion went to completion. On the lean side the percent hydrocarbons (fuel) will also be very low, probably less than .1 percent, so we could also say it went to completion. If you want to talk in terms of burning all the fuel, then the only way to do that is to run at stoichiometric or leaner. The reason the exhaust temperature peaks at a given air/fuel ratio, very slightly lean of stoichiometric, is that there is the lowest quantity of inert material in the mix under that condition. The greater the proportion of inert material the lower will be the temperature. On the rich side the excess fuel can be considered inert, as there is no oxygen available for it to burn. On the lean side there is excess air, the excess oxygen being inert as there is no fuel available with which to react. Note that there are many things that make the system less than perfect. There are differences in air flow between cylinders. There will be differences in exhaust residual in the cylinders caused by variations in port geometry, valve condition, valve timing errors, etc. There is a significant variation in a given cylinder between cycles. This cycle-to-cycle variation is greater in the case of carburetion where variations in atomization and distribution will cause "roughness" before the engine reaches the lean limit. Note that this roughness may not really be bad by itself, as it is mostly a variation from cycle to cycle of the power output of the cylinders, not a misfire. And finally there are air/fuel ratio variations within the cylinder - this is the main reason the percent remaining of neither oxygen or hydrocarbons will go to zero. As you can see, nothing in the process is perfect, but the degree to which variation is reduced will determine how well the system works. I would venture a guess that the "good" fuel-injected engine has only a few tenths of a percent of improvement remaining. This is an engine with all the air flow work taken care of, injectors carefully matched, etc. There are bigger fish to fry with regard to things like ignition timing. Yes, in theory the exhaust temperature of all cylinders should be the same at a given air/fuel ratio. The variables that make them not the same are numerous, but most have to do with the temperature measurement itself. The temperature probe is hit with a blast of very hot gas for a moment and then resides in mostly stagnate exhaust for the rest of the cycle. There are exhaust pulsations and circulation between the cylinder blow-down events that are probably not the same for all cylinders. The air flow pattern around the pipes are different, resulting in some pipes running cooler than others and this cools the probe. The probes may not be in exactly the same relative location, putting them in a different area of the blow-down flow. The bottom line is that we have come to disregard, for the most part, the difference between exhaust temperatures and worry more about the temperature relative to peak for that cylinder. Gary Casey ________________________________ Message 2 _____________________________________ Time: 07:06:55 AM PST US From: "flyv35b" Subject: Re: Engines-List: RE: Engines-List Digest: 8 Msgs - 05/26/04 --> Engines-List message posted by: "flyv35b" I do not believe the thermostat is > necessary in this part of the country. I put over 1600 hours on a Comanche > and never knew about Vernatherms. Of course a filter attachment that > contained a Vernatherm might solve the problem but the question is "can the > engine run without the thermostat, and if so, be legal on a certified > aircraft"? Removing the Vernatherm valve (VV) would make matters worse. The VV does not open and route flow to the cooler as temperature increases. It closes and blocks off the oil path that bypasses the cooler. In other words, as it closes it forces all of the oil to flow through the cooler. It the taper end of the VV does not seat properly on the edge of the hole then it will bypass oil and flow to the cooler will not be as much as it could be. I believe an engine shop can remachine this seat area to a degree. I am wondering if there are other factors that may be aggravating your oil cooling, such as engine baffling condition, restriction internally in the oil cooler itself. You may want to look into these and possibly have the cooler cleaned by a shop specializing in cooler repair and overhaul, or even buy a new cooler. Maybe there is an STC for a larger cooler installation. I have rarely seen an engine installation that the baffling couldn't be improved upon. Cliff A&P/IA ----- Original Message ----- From: "Robert Ardis" Subject: Engines-List: RE: Engines-List Digest: 8 Msgs - 05/26/04 > --> Engines-List message posted by: "Robert Ardis" > > Pardon me for changing the discussion from a 912 Rotax to a O-540 > Lycoming. > The problem with flying the Cherokee 235 is that in Texas this time of > the year the oil temp runs about "a needle's width" from the red line. The > plane came from Utah and had been used in flight training and is equiped > with the 178 degree (85C) Vernatherm. The Vernatherm does not seat > correctly in the accessory case and it appears that the hole which it is > supposed to plug is so badly distorted and rough that a new Vernatherm will > not work much better. > What can be done short of a new accessory case? The reaming of the hole > will require enlarging > the hole beyond limits. Really, in NE Texas, the cooler needs to be 'on > line' as soon as the engine starts. I do not believe the thermostat is > necessary in this part of the country. I put over 1600 hours on a Comanche > and never knew about Vernatherms. Of course a filter attachment that > contained a Vernatherm might solve the problem but the question is "can the > engine run without the thermostat, and if so, be legal on a certified > aircraft"? > > >From: Engines-List Digest Server > >Reply-To: engines-list@matronics.com > >To: Engines-List Digest List > >Subject: Engines-List Digest: 8 Msgs - 05/26/04 > >Date: Wed, 26 May 2004 23:56:29 -0700 > > > >* > > > > ================================================== > > Online Versions of Today's List Digest Archive > > ================================================== > > > >Today's complete Engines-List Digest can be also be found in either > >of the two Web Links listed below. The .html file includes the Digest > >formatted in HTML for viewing with a web browser and features Hyperlinked > >Indexes and Message Navigation. The .txt file includes the plain ASCII > >version of the Engines-List Digest and can be viewed with a generic > >text editor such as Notepad or with a web browser. > > > >HTML Version: > > > > > >http://www.matronics.com/digest/engines-list/Digest.Engines-List.2004-05-26 .html > > > >Text Version: > > > > > >http://www.matronics.com/digest/engines-list/Digest.Engines-List.2004-05-26 .txt > > > > > > ================================================ > > EMail Version of Today's List Digest Archive > > ================================================ > > > > > > Engines-List Digest Archive > > --- > > Total Messages Posted Wed 05/26/04: 8 > > > > > >Today's Message Index: > >---------------------- > > > > 1. 06:03 AM - Re: Lycoming service bulletins (Gary Casey) > > 2. 06:28 AM - Re: lean vs rich (Scott Bilinski) > > 3. 08:24 AM - Re: lean vs rich (Marvin Dupree) > > 4. 09:00 AM - Re: Re: plugs (Healy, Joseph) > > 5. 09:47 AM - Re: Lycoming service bulletins (Christopher Stone) > > 6. 10:43 AM - Re: lean vs rich (Scott Bilinski) > > 7. 07:24 PM - Re: Re: plugs (Lowell Fitt) > > 8. 08:48 PM - Re: Re: plugs (Johnny Johnson) > > > > > >________________________________ Message 1 > >_____________________________________ > > > > > >Time: 06:03:22 AM PST US > >From: "Gary Casey" > >Subject: Engines-List: Re: Lycoming service bulletins > > > >--> Engines-List message posted by: "Gary Casey" > > > >Steve - thanks for the great link! I maneuvered through the Lycoming > >website and came up empty - they present a few SB's, but you have to pay > >$$$ > >for most. > > > >Gary Casey > > > > > >________________________________ Message 2 > >_____________________________________ > > > > > >Time: 06:28:22 AM PST US > >From: Scott Bilinski > >Subject: Re: Engines-List: lean vs rich > > > >--> Engines-List message posted by: Scott Bilinski > > > > > >Yes it is confusing, just the opposite of what you would think. When > >peaking each cylinder one at a time the EGT's should peak about he same > >temp right? So the only real difference is the fuel flow. I have to stand > >by my previous post that the cylinder which peaks with the highest fuel > >flow is the leanest, and yes its fuel flow for all 4 cylinders. Air Flow > >Performance helped me dial in my fuel flow per cylinder. I gave them the > >info they sent me the nozzles and installed them and it brought the fuel > >flow closer together using this method. > > > > > >At 08:40 PM 5/25/2004 -0400, you wrote: > > >--> Engines-List message posted by: TeamGrumman@aol.com > > > > > >Quote: "Yea me to. Apparently the way it works is, the cylinder that > >peaks > > >with the highest fuel flow, means all the other cylinders are getting > >more > > >fuel > > >so its the leanest. *** so the cylinder with the least fuel flow is > >the > > >richest?=A0 somehow, I would have thought the opposite." > > > > > >I think someone is going to have to be a little more specific here. > > >Cylinders with the highest fuel flow, i.e., receiving the most fuel, are > > >the richest > > >cylinders. Now, if you are saying that the cylinder with the first EGT > >to > > >peak at any given fuel flow is the leanest, then I'd agree. I'm making > >the > > >assumption that you are NOT measuring individual fuel flow rates for each > > >cylinder. > > > > > >I admit I got in on this thread at the most recent email so if I am > >missing > > >something, please feel free to let me in on what I'm missing. > > > > > > > > > > > >Scott Bilinski > >Eng dept 305 > >Phone (858) 657-2536 > >Pager (858) 502-5190 > > > > > >________________________________ Message 3 > >_____________________________________ > > > > > >Time: 08:24:18 AM PST US > >Subject: Re: Engines-List: lean vs rich > >From: Marvin Dupree <97corvette@cox.net> > > > >--> Engines-List message posted by: Marvin Dupree <97corvette@cox.net> > > > >scott....i questioned you on this earlier and from your response, i > >thought i had it figured out. but, i read this one and i am still not > >sure. are you saying that --- at highest fuel flow to all cylinders, > >the cylinder that has the highest peak egt is the leanest----? or are > >you saying the individual cylinder with the highest fuel flow is the > >leanest? > >regards, marv > >On Wednesday, May 26, 2004, at 08:25 AM, Scott Bilinski wrote: > > > > > --> Engines-List message posted by: Scott Bilinski > > > > > > > > > Yes it is confusing, just the opposite of what you would think. When > > > peaking each cylinder one at a time the EGT's should peak about he same > > > temp right? So the only real difference is the fuel flow. I have to > > > stand > > > by my previous post that the cylinder which peaks with the highest fuel > > > flow is the leanest, and yes its fuel flow for all 4 cylinders. Air Flow > > > Performance helped me dial in my fuel flow per cylinder. I gave them the > > > info they sent me the nozzles and installed them and it brought the fuel > > > flow closer together using this method. > > > > > > > > > At 08:40 PM 5/25/2004 -0400, you wrote: > > >> --> Engines-List message posted by: TeamGrumman@aol.com > > >> > > >> Quote: "Yea me to. Apparently the way it works is, the cylinder that > > >> peaks > > >> with the highest fuel flow, means all the other cylinders are getting > > >> more > > >> fuel > > >> so its the leanest. *** so the cylinder with the least fuel flow > > >> is the > > >> richest?=A0 somehow, I would have thought the opposite." > > >> > > >> I think someone is going to have to be a little more specific here. > > >> Cylinders with the highest fuel flow, i.e., receiving the most fuel, > > >> are > > >> the richest > > >> cylinders. Now, if you are saying that the cylinder with the first > > >> EGT to > > >> peak at any given fuel flow is the leanest, then I'd agree. I'm > > >> making the > > >> assumption that you are NOT measuring individual fuel flow rates for > > >> each > > >> cylinder. > > >> > > >> I admit I got in on this thread at the most recent email so if I am > > >> missing > > >> something, please feel free to let me in on what I'm missing. > > >> > > >> > > > > > > > > > Scott Bilinski > > > Eng dept 305 > > > Phone (858) 657-2536 > > > Pager (858) 502-5190 > > > > > > > > > > > > > > > > > > > > > >________________________________ Message 4 > >_____________________________________ > > > > > >Time: 09:00:34 AM PST US > >Subject: RE: Engines-List: Re: plugs > >From: "Healy, Joseph" > > > >--> Engines-List message posted by: "Healy, Joseph" > > > >It seems that several people are having the same problem. For that > >reason I doubt that an induction leak or other mechanical explanation is > >the cause. If it were, then the discoloration problem would be random, > >not consistently sooty front plugs with white back plugs. > > > >The problem might be the pattern of cooling air under the cowl resulting > >in a higher mass flow of air/fuel charge entering the front cylinders > >compared with the rear cylinders. For example, if the air/fuel mixture > >entering the front cylinders is at 75 degrees, and that for the rear is > >105 degrees, the front cylinders will receive a 5% greater charge (more > >fuel and air) than the rear cylinders. This is due to the increased > >density of the air/fuel mixture predicted by the ideal gas law and > >assuming a relatively equal manifold pressure at all points in the > >intake. More fuel burnt in the front cylinders will contribute to more > >soot on the plugs compared with the rear cylinders. > > > >Also, if the intake manifold is experiencing a front to back > >differential in temperature, then the cylinders will likewise have a > >differential temperature front to back. The rear cylinders, being > >hotter, will have more complete combustion and less soot than the front. > > > >Note, this is not a question of too much cooling vs. too little cooling. > >It is the differential cooling effect at various points on the engine > >that would cause the problem. > > > >Joe Healy > > > > > >-----Original Message----- > >From: kyle Ponsford [mailto:wild_kyle@hotmail.com] > >Subject: Re: Engines-List: Re: plugs > > > > > >--> Engines-List message posted by: "kyle Ponsford" > >--> > > > >The intake manafolds connect the front and rear cylinders, and obviously > > > >they are not perfect because I am learning lots of owners have collor > >discrepency between front and rear. but do we know why? > > > > > > Kinda hard to miss read a WHITE plug! and I do mean chalky white. > > > > but no aluminum particles. the front plugs are so black and sooty > > > > they foul at about 4 hours. it is hard for me to imagin guys flying > > > > the things like that. > > > > > >________________________________ Message 5 > >_____________________________________ > > > > > >Time: 09:47:34 AM PST US > >From: Christopher Stone > >Subject: Re: Engines-List: Lycoming service bulletins > > > >--> Engines-List message posted by: Christopher Stone > > > > > >I will send you a copy (.pdf) off list of the SI 1425a > > > >Chris Stone > > > >-----Original Message----- > >From: Gary Casey > >Subject: Engines-List: Lycoming service bulletins > > > >--> Engines-List message posted by: "Gary Casey" > > > >I have been trying, with no luck, to find a copy of Lycoming Service > >Bulletin SB388B and Service Instruction 1425A. Can anyone help? > > > >Gary Casey > > > > > >________________________________ Message 6 > >_____________________________________ > > > > > >Time: 10:43:35 AM PST US > >From: Scott Bilinski > >Subject: Re: Engines-List: lean vs rich > > > >--> Engines-List message posted by: Scott Bilinski > > > > > >Lets try this one more time. You look at one cylinder at a time, peak the > >EGT, and note the fuel flow meter reading (which is all cyl fuel flow). Do > >this on all cylinders. Look at the numbers and the cylinder that shows the > >highest fuel flow, is the leanest. I put a larger nozzle in it and the > >numbers come closer together. I really dont know another way to explain it. > > > > > >At 10:22 AM 5/26/2004 -0500, you wrote: > > >--> Engines-List message posted by: Marvin Dupree <97corvette@cox.net> > > > > > >scott....i questioned you on this earlier and from your response, i > > >thought i had it figured out. but, i read this one and i am still not > > >sure. are you saying that --- at highest fuel flow to all cylinders, > > >the cylinder that has the highest peak egt is the leanest----? or are > > >you saying the individual cylinder with the highest fuel flow is the > > >leanest? > > >regards, marv > > >On Wednesday, May 26, 2004, at 08:25 AM, Scott Bilinski wrote: > > > > > > > --> Engines-List message posted by: Scott Bilinski > > > > > > > > > > > > Yes it is confusing, just the opposite of what you would think. When > > > > peaking each cylinder one at a time the EGT's should peak about he > >same > > > > temp right? So the only real difference is the fuel flow. I have to > > > > stand > > > > by my previous post that the cylinder which peaks with the highest > >fuel > > > > flow is the leanest, and yes its fuel flow for all 4 cylinders. Air > >Flow > > > > Performance helped me dial in my fuel flow per cylinder. I gave them > >the > > > > info they sent me the nozzles and installed them and it brought the > >fuel > > > > flow closer together using this method. > > > > > > > > > > > > At 08:40 PM 5/25/2004 -0400, you wrote: > > > >> --> Engines-List message posted by: TeamGrumman@aol.com > > > >> > > > >> Quote: "Yea me to. Apparently the way it works is, the cylinder that > > > >> peaks > > > >> with the highest fuel flow, means all the other cylinders are getting > > > >> more > > > >> fuel > > > >> so its the leanest. *** so the cylinder with the least fuel flow > > > >> is the > > > >> richest?=A0 somehow, I would have thought the opposite." > > > >> > > > >> I think someone is going to have to be a little more specific here. > > > >> Cylinders with the highest fuel flow, i.e., receiving the most fuel, > > > >> are > > > >> the richest > > > >> cylinders. Now, if you are saying that the cylinder with the first > > > >> EGT to > > > >> peak at any given fuel flow is the leanest, then I'd agree. I'm > > > >> making the > > > >> assumption that you are NOT measuring individual fuel flow rates for > > > >> each > > > >> cylinder. > > > >> > > > >> I admit I got in on this thread at the most recent email so if I am > > > >> missing > > > >> something, please feel free to let me in on what I'm missing. > > > >> > > > >> > > > > > > > > > > > > Scott Bilinski > > > > Eng dept 305 > > > > Phone (858) 657-2536 > > > > Pager (858) 502-5190 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >Scott Bilinski > >Eng dept 305 > >Phone (858) 657-2536 > >Pager (858) 502-5190 > > > > > >________________________________ Message 7 > >_____________________________________ > > > > > >Time: 07:24:07 PM PST US > >From: "Lowell Fitt" > >Subject: Re: Engines-List: Re: plugs > > > >--> Engines-List message posted by: "Lowell Fitt" > > > >Joe's post pretty much explains the plug issue. The vast majority of the > >engines in these configurations do not have baffling so the temp > >differential will be there. > > > >If the front plugs are fouling then my thought is that the mixture is too > >rich. That won't take care of the white plugs on the rear, but as I have > >said earlier, the color differential is not an issue for most 912 users. I > >have heard Erik Tucker the recognized Rotax Guru speak on a couple of > >occasions and this issue has never come up. My humble suggestion would be > >to adjust the mixture to get a dark but not fouling sooty color to the > >front plugs and go fly. Without a redesign of the induction system the > >color differential will persist and I honestly don't think Rotax thinks it > >to be a problem especially with the millions of hours on these engines. > > > >If a problem arises, Rotax is also very quick to announce problems with > >service bulletins. After only three or four instances with the stator > >shorting, they provided free parts and free loner tools for upgrades. And > >the problems that arose were with the certified version of the 912 used in > >trainers. The free fix was never-the-less available to all. > > > >Lowell > >----- Original Message ----- > >From: "Healy, Joseph" > >Subject: RE: Engines-List: Re: plugs > > > > > > > --> Engines-List message posted by: "Healy, Joseph" > > > > > > It seems that several people are having the same problem. For that > > > reason I doubt that an induction leak or other mechanical explanation is > > > the cause. If it were, then the discoloration problem would be random, > > > not consistently sooty front plugs with white back plugs. > > > > > > The problem might be the pattern of cooling air under the cowl resulting > > > in a higher mass flow of air/fuel charge entering the front cylinders > > > compared with the rear cylinders. For example, if the air/fuel mixture > > > entering the front cylinders is at 75 degrees, and that for the rear is > > > 105 degrees, the front cylinders will receive a 5% greater charge (more > > > fuel and air) than the rear cylinders. This is due to the increased > > > density of the air/fuel mixture predicted by the ideal gas law and > > > assuming a relatively equal manifold pressure at all points in the > > > intake. More fuel burnt in the front cylinders will contribute to more > > > soot on the plugs compared with the rear cylinders. > > > > > > Also, if the intake manifold is experiencing a front to back > > > differential in temperature, then the cylinders will likewise have a > > > differential temperature front to back. The rear cylinders, being > > > hotter, will have more complete combustion and less soot than the front. > > > > > > Note, this is not a question of too much cooling vs. too little cooling. > > > It is the differential cooling effect at various points on the engine > > > that would cause the problem. > > > > > > Joe Healy > > > > > > > > > -----Original Message----- > > > From: kyle Ponsford [mailto:wild_kyle@hotmail.com] > > > To: engines-list@matronics.com > > > Subject: Re: Engines-List: Re: plugs > > > > > > > > > --> Engines-List message posted by: "kyle Ponsford" > > > --> > > > > > > The intake manafolds connect the front and rear cylinders, and obviously > > > > > > they are not perfect because I am learning lots of owners have collor > > > discrepency between front and rear. but do we know why? > > > > > > > > Kinda hard to miss read a WHITE plug! and I do mean chalky white. > > > > > but no aluminum particles. the front plugs are so black and sooty > > > > > they foul at about 4 hours. it is hard for me to imagin guys flying > > > > > the things like that. > > > > > > > > > > > >________________________________ Message 8 > >_____________________________________ > > > > > >Time: 08:48:38 PM PST US > >From: "Johnny Johnson" > >Subject: RE: Engines-List: Re: plugs > > > >--> Engines-List message posted by: "Johnny Johnson" > > > >From a lurker that knows basically nothing about 912's but feels compelled > >to comment... IIRC you said this happens on both sides, so maybe it is just > >plain bad design of the intake runners or something. It sounds like a > >pretty major difference in mixture and so just doesn't seem like it would > >be > >designed to run that way... but, I may be all wet. > > > >In any event and FWIW, I think I would want to be certain there are no > >induction system leaks causing the lean mixture in the "white cylinders" > >before I leaned it out some more. A bent or warped flange, loose fastener, > >bad gasket, really lousy intake manifold to block fit, holes in a casting > >or > >weld, something like that. It might be impossible to spot the culprit with > >the Mk I eyeball--a way to check for leaks with the engine running has been > >previously suggested but, as noted, can be a bit dicey with a prop > >spinning... figuring a way to safely do that test would be well worth the > >effort IMHO. Having satisfied myself that there are no leaks, I guess I > >would then lean it a tad and go flying, as Lowell suggests. > > > >Best of luck--hopefully you can get in the air very soon, with calmness of > >heart :=)) > > > >Johnny > > > > -----Original Message----- > >From: owner-engines-list-server@matronics.com > >[mailto:owner-engines-list-server@matronics.com] On Behalf Of Lowell Fitt > >Subject: Re: Engines-List: Re: plugs > > > >--> Engines-List message posted by: "Lowell Fitt" > > > >Joe's post pretty much explains the plug issue. The vast majority of the > >engines in these configurations do not have baffling so the temp > >differential will be there. > > > >If the front plugs are fouling then my thought is that the mixture is too > >rich. That won't take care of the white plugs on the rear, but as I have > >said earlier, the color differential is not an issue for most 912 users. I > >have heard Erik Tucker the recognized Rotax Guru speak on a couple of > >occasions and this issue has never come up. My humble suggestion would be > >to adjust the mixture to get a dark but not fouling sooty color to the > >front plugs and go fly. Without a redesign of the induction system the > >color differential will persist and I honestly don't think Rotax thinks it > >to be a problem especially with the millions of hours on these engines. > > > >If a problem arises, Rotax is also very quick to announce problems with > >service bulletins. After only three or four instances with the stator > >shorting, they provided free parts and free loner tools for upgrades. And > >the problems that arose were with the certified version of the 912 used in > >trainers. The free fix was never-the-less available to all. > > > >Lowell > >----- Original Message ----- > >From: "Healy, Joseph" > >Subject: RE: Engines-List: Re: plugs > > > > > > > --> Engines-List message posted by: "Healy, Joseph" > > > > > > It seems that several people are having the same problem. For that > > > reason I doubt that an induction leak or other mechanical explanation is > > > the cause. If it were, then the discoloration problem would be random, > > > not consistently sooty front plugs with white back plugs. > > > > > > The problem might be the pattern of cooling air under the cowl resulting > > > in a higher mass flow of air/fuel charge entering the front cylinders > > > compared with the rear cylinders. For example, if the air/fuel mixture > > > entering the front cylinders is at 75 degrees, and that for the rear is > > > 105 degrees, the front cylinders will receive a 5% greater charge (more > > > fuel and air) than the rear cylinders. This is due to the increased > > > density of the air/fuel mixture predicted by the ideal gas law and > > > assuming a relatively equal manifold pressure at all points in the > > > intake. More fuel burnt in the front cylinders will contribute to more > > > soot on the plugs compared with the rear cylinders. > > > > > > Also, if the intake manifold is experiencing a front to back > > > differential in temperature, then the cylinders will likewise have a > > > differential temperature front to back. The rear cylinders, being > > > hotter, will have more complete combustion and less soot than the front. > > > > > > Note, this is not a question of too much cooling vs. too little cooling. > > > It is the differential cooling effect at various points on the engine > > > that would cause the problem. > > > > > > Joe Healy > > > > > > > > > -----Original Message----- > > > From: kyle Ponsford [mailto:wild_kyle@hotmail.com] > > > To: engines-list@matronics.com > > > Subject: Re: Engines-List: Re: plugs > > > > > > > > > --> Engines-List message posted by: "kyle Ponsford" > > > --> > > > > > > The intake manafolds connect the front and rear cylinders, and obviously > > > > > > they are not perfect because I am learning lots of owners have collor > > > discrepency between front and rear. but do we know why? > > > > > > > > Kinda hard to miss read a WHITE plug! and I do mean chalky white. > > > > > but no aluminum particles. the front plugs are so black and sooty > > > > > they foul at about 4 hours. it is hard for me to imagin guys flying > > > > > the things like that. > > > > > > > > > > > > ________________________________ Message 3 _____________________________________ Time: 12:18:32 PM PST US From: "B.P." Subject: Engines-List: Re: lean vs rich --> Engines-List message posted by: "B.P." I really thought someone more qualified than me would have jumped in by now; The usual of "I'm not an expert, etc."., "no warranties, etc." apply here. Some years ago while attending Lycoming's factory engine school this was discussed. It seems many of the "fuel flow" gauges don't measure fuel flow at all but calculate it based on the facts that if a known pipe size (fuel line) with a fixed orifice (injector) has it's line pressure varied you can calculate the liquid flow through the orifice. The gauges directly measure PSI (pounds per square inch) and not fuel flow. Conversely now if we have a constant fuel flow through a pipe and suddenly shrink the size of the orifice (plugged injector) guess what happens to our "fuel flow" gauge; the line pressure goes up (and the GPH reading) since our gauge is calibrated in GPH (or other quantity). Think of your fuel gauge as a line pressure gauge only and all this makes sense. I love it when all parties are right and don't know it. Ben List Lurker ________________________________ Message 4 _____________________________________ Time: 02:07:29 PM PST US From: "Gordon and Marge" Subject: RE: Engines-List: RE: air/fuel ratios --> Engines-List message posted by: "Gordon and Marge" -----Original Message----- From: owner-engines-list-server@matronics.com [mailto:owner-engines-list-server@matronics.com] On Behalf Of Gary Casey Subject: Engines-List: RE: air/fuel ratios --> Engines-List message posted by: "Gary Casey" Gary, et al: Perhaps we are overcomplicating things. Think of it this way: If we may assume that there is variation among cylinders and that we are operating at full rich initially, all cylinders are on the rich side of peak. As the mixture is leaned, the cylinder that reaches peak EGT first has the leanest mixture since all the others are still on the rich side of peak. Now if we were to approach peak EGT from a position of extreme lean by enriching the mixture then the first cylinder to peak would be the richest. Or so it seems to me. Gordon Comfort N363GC