The 355-Exposed? Covered Up? or Overlooked ???? | Page 7 | FerrariChat

The 355-Exposed? Covered Up? or Overlooked ????

Discussion in '348/355' started by bcwawright, Jun 5, 2007.

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  1. bcwawright

    bcwawright F1 Veteran

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    #151 bcwawright, Aug 21, 2007
    Wella,wella,wella, moving right along here folks...at a dead snails pace...lol

    It is extremely hard,if not impossible for me to change my way of thinking or approach when it comes to engine design/build.

    Having only 40 years of experience with turbo engine developement, primarly of the Porsche marque, the complexities of dealing with an NA engine have, to say the least, challenged me to the limit and beyond. If I have learned only one thing from this project, it would be that producing a high output reliable NA engine is far more complex than developing a compressor type HO engine. If one takes "ferrarifixers" advice and goes the turbo route, 90+% of all this crap can be tossed out the window..lol.

    My posts concerning the exhaust wave reversion may not be of importance for the majority of 355 owners, and may only be a concern if you were running in the world endurance series type of racing. Nevertheless, what I have posted is true, and is an area I believe is of value not only to the performance/reliability of the 355, but all NA HO engines.


    Due to the fact that the 355 has no variable intake(360 has a 2 stage,and the whopping 3 stage-Audi,Jaguar,Porsches' Varioram), no variable valve train(now the norm on most engines),a quasi/pseudo variable exhaust(by-pass), and a 5.2 Motronic(96-on) ECU with no "unlock" protocols, the quest for even higher performance, with reliabilty is a long road filled with compromises. If one takes this route, be forewarned....it is not for the penny pincher,non-techy, or faint of heart.

    Having said that I want to make some things perfectly clear:

    1. The purpose and intent of this thread is to look at the major reliability issues of the 355. At the beginning I stated that we would leave NO stone unturned in this quest for understanding, and what was/is stated about the exhaust system is just another stone that we are looking under.

    2. Even though I may talk about the exhaust or things that appear to be performance enhancements, this thread is NOT about turning your 355 into a screamin banchee or race car,period. Tuning or modifying the 355 engine to "kicka*s", deserves its own thread.

    In an effort to respond to certain questions posted earlier I will try and address the term "over-scavenged". To do this in light of a street car you must at least understand a few things which apply to both single and dual plane crankshaft engines(albiet there are some big differences also between the 2, but we will look at things here in a general way):

    1. Long Duration Cams: Open exhaust valves earlier, allowing combustion pressure to force exhaust gases out of the system. The 4 stroke engine turns 720 degrees to complete its cycle. If exhaust duration is increased, some other stroke must lose an equal number of degrees. Usually the power stroke is robbed, to supplement the exhaust stroke, reducing the thermodynamic efficiency of the engine (shorter power stroke). With a shorter power stroke, the mixture has less time to burn before the exhaust valve opens, dumping hotter, still burning gases into the header, burning valves, increasing cylinder head heat load, cooking headers and wasting energy that should be converted to crankshaft horsepower.

    2. Catalytic Converters: Restrict exhaust flow, increasing back pressure, and reducing scavenge. Over-scavenged, unburned air/fuel burns in the converter, causing it to overheat and prematurely fail. Rarely can converters and scavenge co-exist in a beneficial environment due to converter restriction and air/fuel over-scavenge.

    3. Scavenge, created and maintained by a resonant header, does not remove burned gases from the combustion chamber of an internal combustion engine. As the combustion mixture is burned during the power stroke, the mixture begins its burn from the sparkplug and continues burning toward the descending piston. When the exhaust valve opens in the latter portions of the piston's descent, the gases nearest the valve, and sparkplug, are the first to leave the chamber, under hundreds or even thousands of pounds per square inch pressure. As the light, hot, energetic combustion product gases pass out of the chamber through the exhaust port, chamber pressure drops as potential energy (cylinder pressure) is converted into kinetic energy (exhaust gas velocity). This high velocity exhaust gas column then tends to stay in motion, even after all of the hot, burned, exhaust gases have left the chamber and the chamber pressure drops to zero. Scavenge is then created as the still rapidly exiting exhaust gas column evacuates the chamber by sucking any unburned air/fuel, remaining at the bottom of the chamber, out the exhaust port. No dynamic cylinder pressure increase here.
    About 60 degrees before the end of the exhaust stroke, the intake valve opens, exposing the intake tract to the scavenge created vacuum now in the combustion chamber. If the scavenge vacuum is greater than manifold vacuum at that instant (say the throttle is wide open), air/fuel mixture will be sucked out of the intake manifold, through the combustion chamber, past the still open exhaust valve, and out the tail pipe. No dynamic cylinder pressure increase here. In fact, cylinder pressure will be reduced in the very next compression cycle because a portion of the available air/fuel has been lost, never to be burned. Opps, looks like you have just lost dynamic cylinder pressure...the one thing needed to make power.

    Now most people say that the "fuel mixture" must be made "richer in fuel", when a scavenge header is installed. The reason is, that the header's powerful scavenge allows the engine to breath better, burning more air/fuel, making more horsepower.
    The truth is that fuel must be added because the scavenge header is sucking the same amount of fuel, the amount that must now be added, out the tailpipe; the phenomenon is known as "over-scavenge".

    All intake systems compensate for airflow changes by proportionately adding fuel to air passing through the intake. Carburetors use a simple Ventura that generates a stronger vacuum signal with greater airflow, pulling more fuel through jet circuits, spraying it into the intake air stream. Fuel injection systems use various airflow sensors and air/fuel maps to precisely meter fuel to match air flow. So, even if intake air flow were to increase because of the installation of a scavenge header, the correct amount of fuel would always be added; there would be no need to rejet or remap air/fuel mixtures.
    Typically, the more highly tuned the header, and the less the back pressure after the header (i.e. mufflers or catalytic converter restriction), the greater the over scavenge generated and the greater the amount of fuel that must be added to the fuel delivery curve. The additional fuel has to be added because an equal amount of the originally jetted or mapped fuel is lost. How? By "over-scavenge" of the initial air/fuel charge, the richest portion of all air/fuel delivered to the combustion chamber. How do we know this? Because (1) fuel economy (BHPHR/#fuel) does not improve, (2) the mixture leans out only at the scavenge power peak (resonance) rpm, it becomes richer (needs less supplemental fuel) below and above that rpm, & (3) HC (unburned hydrocarbon) emissions go up within such tuned rpm range.
    Scavenge quickly becomes over scavenge, sucking the richest portion of delivered air/fuel out of the intake manifold and through the combustion chamber during the 60 or so degrees of valve overlap, when both intake and exhaust valves are open at the same time.
    Ironically, 3, 4 and 5 valve engines are the most likely engines to suffer over scavenge due to the much greater valve curtain from which air/fuel is allowed to escape under minimal vacuum conditions. High flow or ported 2 valve heads suffer the same fate due to increased air flow propensity. So, the better the head, the more likely that scavenge will become over scavenge, and dynamic cylinder pressure will drop.

    Long duration exhaust cams are necessary with scavenge headers because such headers convert exhaust gas velocity into scavenge, slowing the rate at which exhaust gases can escape from the engine. Longer duration exhaust cams give the exhaust stroke more time to blow down exhaust gases. Longer duration exhaust cams give that unmistakable big cam (stumbling) idle, because at idle the intake vacuum is the greatest & scavenge is the weakest, allowing exhaust gases to be sucked into the intake manifold during valve overlap, diluting intake manifold mixture, which in the subsequent intake stroke, fills the combustion chamber with inert exhaust gases that don't burn, causing a misfire (stumble).


    To be perfectly honest, there are many many theories, conjectures, opinions,etc on all this back-pressure,scavenge,resonance tuning stuff....that is just one...and the one I fully support.

    So what does all this nonsense mean? How does this tie into 355 reliability issues/concerns? PLEASE NOTE:I AM STILL ON THE VALVE GUIDES....haven't even really begun yet, to address the exhaust!!!!!!

    Well, I'll try to wrap all of this babbling up into two nice little pills for you to swallow:

    1. Long duration cams(ala 355) can "heat load" the cylinder head. How much of that can the little copper-alloy guide take?

    2. The reversion wave during overlap can contaminate the intake bowl...with either hot(hmmm..wonder if it's still burning?) exhaust gas, or hot exh. gas combined with degraded header(metallic) particles. Ain't that just a pretty scenerio?? Could all of this effect the valve guide or the intake valve stem that slides inside the guide?

    OK.........I need some help with this. Maybe I'm all wrong. Anybody got some worthy comments or opinions they would like to share?
     
  2. No Doubt

    No Doubt Seven Time F1 World Champ

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    #152 No Doubt, Aug 21, 2007
    You have the pictures of the failed valve guides in this very thread.

    If you see pitting on the failed valve guides, then the exhause reversion wave should be considered as a potential cause of valve guide failure. If not, then don't.
     
  3. bcwawright

    bcwawright F1 Veteran

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    #153 bcwawright, Aug 21, 2007
    ND, I could only wish it were that simple.

    External pitting of the guide proper just confirms the presence of header particles in the intake bowl or exh. bowl. The pitting may be so small that it can only be detected under microscopic examination....that would definitely not show up on a posted picture.

    External pitting only,IMO, would not necessarily effect the guide function(keep in mind that the pitting you are implying will just appear on the small tip of the guide which projects into the intake or exh. port). The guide would suffer, IF some of the header material molecules adhered to the valve stem(when in the open position) and then were carried back up into the guide bore when the valve was in the fully closed position. There is an extremely small clearance in this bearing set-up....so much so that even at the molecular level, enough contamination would degrade the guide bore.

    I am fully aware of the fact, that what I'm implying here is waaaaaay out in left field...even to the point of being absurd and rediculous. But, nevertheless A POSSIBILITY.

    Again, in looking at the valve guide failure, ALL POSSIBILITIES must be put on the table....no matter how small. This along with any other possibilities can be easily discarded if found to be non-contributing.
     
  4. bcwawright

    bcwawright F1 Veteran

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    #154 bcwawright, Aug 21, 2007
    This thread is not for the typical Ferrari owner, of which approx. 99.99999% are more concerned about their sticky interior or which car wax to use.

    In a purpose built racing engine, engineers look at engine cycles. As an example: At the LeMans 24hr race our engines were registering in the data logger close to 10,000,000 cycles at the end of this event. Afterwards they were torn down and an exhaustive analysis done. The extent of the analysis varies within each teams engineering capabilities and budget.

    However, on a street car it may be years or 10s of thousands of miles before an engine is removed and torn down.

    Even then the analysis to diagnose a problem is, in many cases, minimal at the very best. VERY VERY rarely is a micrscopic,chemical,or metallurgical analysis done, and that is usely only done by the mfg after many many failures are reported.

    It is important to remember that any degratory process,once started,continues.....and that one process usually sets other degratory processes into motion. There are no self healing engines YET...lol. By the time everything falls apart the signs of the original causation(the first event that got everything started) may be long gone,i.e it is so masked and covered up by layers of other processes that this "first event process" is undetectable without an exhaustive/extensive, and usually highly expensive, failure analysis.

    Let me give you a hypothetical example of this using the header thingy we've discussed in the last several posts:

    You crank your car up and hear the exhaust death rattle/ticking noise. Take it to a shop and guess what??....yes sirree Bob, the old crappy stock headers are shot.
    Okeee dokeee, changeum out with some brand spankin new ones....and your good to go...right?? Well, now you know the headers are shot, what happened to all the metal while it was degrading to the point you finally noticed it??
    A year or two has gone by since the new headers were installed(let's say that during this period you have put a couple thousand miles on the car) and you are now noticing smoke coming out of the exhaust at start up which goes away in a few minutes. Hmmmm....so you take the car to the shop and sure enough you get the dreaded news that the valve guides need replacing. Shop pulls the heads, sees the guides wallowed out like a 60 year old prostitutes privates, and it goes to the head shop for an overhaul. You ask the shop why, and you get.."all the 355 guides are bad on pre98 year models".....
    IF, header material contamination in the int/exh bowl degrades the guide bore; then, when the degradation of the header first started is when the valve guide bore(clearance) degredation began. Once the bore clearance was opened up, it was all down hill from there, even though you put new headers on. Since the shop didn't have a clue of this even being a possibility they just put new headers on, and being clueless to begin with they didn't examine the heads later during the head rebuild. Instead they sang the 355 national anthem...."Bad Guides-Bad Guides,What U Owners Gonna Do".

    Let's see...degrading headers, starts degrading guides, which lead to burnt valves, which leads to fuel injector problems, etc. Hey,might as well throw in a cat or two, and while we are at it some good ole O2 sensors. Yummie...what a delicious receipe!! But sad to say a little toooo expensive for my taste.


    Please...this is just a hypothetical scenerio!!!!!!!

    Remember this: NO ONE IS EVER GOING TO LOOK FOR something they NEVER considered possible.
     
  5. davehelms

    davehelms F1 Rookie

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    #155 davehelms, Aug 21, 2007
    Now you are cooking at full boil. Keep it up, great post.
    Now to identify the cause of the lean spots..............

    Dave
     
  6. gothspeed

    gothspeed F1 World Champ

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    #156 gothspeed, Aug 21, 2007
    Great posts there bruce!!! There are few people that will go to this extent in the quest for cause and effect :)!!!
     
  7. bcwawright

    bcwawright F1 Veteran

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    #157 bcwawright, Aug 21, 2007
    That is the simpliest question I've been asked in months.

    The "leanest spot" identified so far, is my bank account!! The cause, is me wasting my valuable time on FChat...lol
     
  8. J.P.Sarti

    J.P.Sarti Guest

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    #158 J.P.Sarti, Aug 21, 2007
    The easy answer would be if every 355 has had or will have a guide failure but they don't, percentage wise the odds are the majority will not which throws unknowns into the mix, why?

    Driving habits? Does the owner drive the snot out of the car before fully warm?

    Fuel used? Cheap fuel or bad brands can cause detonation, I have heard it myself using Shell Premium from a single nozzle per 3 grades pump, perhaps some owners also use additives to keep valves clean such as Techron

    Some owners may baby their cars never redlining them causing carbon which increases heat in the combustion chamber

    One thought a stuck bypass valve could be a contributor, I believe cats that are failing can be a major culprit causing heat and backpressure



    Porsche had a big problem with the 2.7L 911 and guides failed from 30000-60000 miles from high heat and using soft copper alloy, they went to silicon bronze in the 930 and SC motors fixing the problems as an Sc motor could last 200000 miles, then the 84 on Carrera had premature valve guide wear on intakes again some attributed to using Mobil 1 synthetic
     
  9. Llenroc

    Llenroc F1 Rookie
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    #159 Llenroc, Aug 21, 2007
    Very well said Dave as always. Most importantly your first paragraph, too many no-it-alls leading the unknowledgeable down a dark path and when you try to correct them YOU get sh@t on. This board has lost a lot of good people because of the guys that HAVE to be right no matter what. I have a lot of first hand experiance on this subject but of course none of it could be correct, so I gave up and now most of the time just lurk and laugh. Hope you figure out the problem Dave, thanks for the input. Regards, Vern
     
  10. gothspeed

    gothspeed F1 World Champ

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    #160 gothspeed, Aug 22, 2007

    .......................:confused: ...................... I did not know there there was anyone who "knows it all"............:rolleyes:......... and now there is someone mighty enough to correct him :eek:???!!! Can anything be done before all the now determined "unknowledgeable" are led astray???.................. all the while........................ wisdom laughs in the distance.....:( ...



    Stay tuned for the next episode........of reputations, daggers and "being wrong is a bad thing" ................... until then .............. can the mystery of the faultering guides be found before we lose any more "good people"?? Is there personal agendas at play here??? Will antipathy rise???.......or.......... can objective posts prevail over sarcastic and condesending posts (like mine) :(??


    ..................I sure hope so........... and here I thought, this was only a forum................... :(







    BTW, thanks for having the courage to start and continue to post on this thread bcawright!!!! Its great to see someone share their knowledge and experience without disenchanting those who want to learn without being talked down to :).....
     
  11. davehelms

    davehelms F1 Rookie

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    #161 davehelms, Aug 22, 2007
    Damn Goth, there is a whole web site for you to play these games, leave this thread to those that want to discuss a problem of a technical nature.

    Bruce and I have spent many hours on the phone discussing these issues, possible solutions and the next series of tests. It is when our theories disagree that the truely productive time is spent. Needless to say I have been wrong more than I have been right while working through this excerise. Bruce's background, knowledge and ideas are priceless in working towards a final solution. It is both of our jobs and agreements to one another to question each others theories and find the weak points. It is when we are in complete agreement on any one finding that I get nervous. This is how designs and ideas evolve in the racing field. Teams of engineers working together to find and perfect a single idea and then fit the idea on a whole package and make it actually work without adversly effecting something else.


    "Remember this: NO ONE IS EVER GOING TO LOOK FOR something they NEVER considered possible."

    Wise words to be read over and over again. Follow that with:

    "In physical science the first essential step in the direction of learning any subject is to find principles of numerical reckoning and practicable methods for measuring some quality connected with it. I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of Science, whatever the matter may be."

    Vern,

    I have read your posts time and again and have printed them out. I refer back to them often while working through these issues and have a list of questions in the "Vern file" to run past you in a short time. Bruce and I have spoken about many of your posts and put a great deal of merit to what you have written in the past. We will be using you as a think tank to critique many of the final theories.
    I too have taken your position and now lurk more than respond. Involving myself in many of these threads amounts to an attempt at professional suicide. Ferrari service has changed a great amount in the last dozen years, some for the good, some for the bad. I for one am not smart enough to be a judge to which is which.


    It seems each time Bruce and I talk the final topic is related to boosting performance of the 355. For me it has muddied the water as I am now very intrigued by a great many thoughts regarding this topic. Last weekend the TIG welder got fired up and some of these ideas are being worked on as a mental vacation from the headers, guides, liners.......... Bruce, make sure you put a heavy screen on the snorkle to keep kids and small pets out of the intake track.

    Dave
     
  12. gothspeed

    gothspeed F1 World Champ

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    #162 gothspeed, Aug 22, 2007
    Dave,

    I believe you know what I was adresssing it that "gravely offensive" post. I personally do not want to read about "dark expensive paths" and how the "unknowledgeable" need to be shielded from the "know it alls". None of those types of posts are productive or contributory IMO. My post was an obvious intentional magnification of those posts, only to show how annoying they can be. If it was too offensive, then I apologize. :eek:

    This thread has been mostly filled with great information and knowledge exchanges. Even when technical disagreements arise, as you said there should be growth from that. So yes, I also believe that this thread should be kept technical in nature and hopefully objectiveness will prevail and some of the many known 355 issues can be put on the table and discussed, as this thread was originally intended. :)
     
  13. Llenroc

    Llenroc F1 Rookie
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    #163 Llenroc, Aug 22, 2007
    Hey oz or is that Mr. OZ... just kidding, thought I should tug on that rope that holds you down, hahaha. Maybe I should have elaborated on what I was getting at above. My thought was that the header problem could probably have been solved by now if some of the first hand knowledgable along with the experianced Ferrari techs that are here(and the ones that are no longer here) were allowed to speak on topics like this without all the riff raff jumping in there,not saying that it has happened on this thread,but this is an important issue to figure out and we need all the experianced we can get. I agree this thread has been better than most of them but the problem here is that we are missing a few folks that use to post here and don't anymore. Regards, Vern
     
  14. Llenroc

    Llenroc F1 Rookie
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    #164 Llenroc, Aug 22, 2007
    Dave, I have a question for you. I think that it has already been answered in a round about way but let me give you some back ground on my question first. I am able to run on occasion my 2.7 without the 02 sensors connected. Remember I don't have the cats(upper or lower) on my exhaust nor do I have the air pump. Since the 2.7 only uses the 02s at idle and part throttle I was curious how it would drive without them, ie; using the fuel maps without the fine tuning of the sensors(14.7:1). I use an Innovate LM-1 with broad band 02 sensor to read and monitor the air to fuel ratio at different rpms and throttle openings. I leave the 02s connected to the ECUs so that they will read the oxygen level in the air(to fool the ECUs into a lean read) the engine runs at about 12:1 at idle and steady state throttle, of course the engine runs a little stronger and smoother BUT (after all that blathering) when I take temp readings of the headers pipes(all 8), about an inch away from the head, the temps are quite a bit lower than when the 02s are in their spot and doing their job in the exhaust system. After all that, my question is if we 355 owners just had the headers duplicated in a far better material (not so much a custom design to make better power as Bruce would like) the heat this motor produces shouldn't bother them, correct?. I guess we all have come to the conclusion that heat is what is destroying the headers(combination of the shields, cats, bypass valve and air pump). My factory headers still seem to be fine but I don't have any of the previously mentioned heat traps on my engine and the headers are ceramic coated. Just a side note, my right side header when the car was raced only had 6500 miles on it when it had to be replaced and there were holes in every tube the left side is still the original and appears to fine. I am not sure it would be if it still had all the heat traps connected to it.
    On another note, if in fact the 355 is ingesting bits of metal from the header than that is probably the reason there has been some liner failures(I'm still leaning on the cheap materials theory but then what the hell do I know). On the header I replaced I didn't notice any delamination of the inside of the tube or any silver flecks on the exhaust ports(I did take some pics of the area) Anyway just some thoughts, Regards, Vern
     
  15. Llenroc

    Llenroc F1 Rookie
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    #165 Llenroc, Aug 22, 2007
    O2 sensors maybe? 14.7:1 is fairly lean for a hi perf. engine attached to cats, exhaust flow cut off valves, airpumps, header heat shields. Match that to them camshafts that help this tiny engine produce all the power it does and crap there go the headers and what ever else gets in the way.
     
  16. davehelms

    davehelms F1 Rookie

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    #166 davehelms, Aug 23, 2007

    Make that foolishly expensive paths and then your statement is accurate. Like it or not, doesn't matter to me. The simple fact is the above statements are accurate and truthful (albeit not productive or contributory) and is coming from someone that has to charge folks to fix senseless problems created by this.

    It has been suggested to me to "grow some skin" to remedy the problem. As annoying as I found that response when it was given to me I will not suggest it to others.
    Just remember, in this age of the Net, He who yells the loudest, must be the righest!? If it smell like a fish.....

    Dave
     
  17. davehelms

    davehelms F1 Rookie

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    #167 davehelms, Aug 23, 2007
    Dave, I have a question for you. I think that it has already been answered in a round about way but let me give you some back ground on my question first. I am able to run on occasion my 2.7 without the 02 sensors connected. Remember I don't have the cats(upper or lower) on my exhaust nor do I have the air pump. Since the 2.7 only uses the 02s at idle and part throttle I was curious how it would drive without them, ie; using the fuel maps without the fine tuning of the sensors(14.7:1). I use an Innovate LM-1 with broad band 02 sensor to read and monitor the air to fuel ratio at different rpms and throttle openings. I leave the 02s connected to the ECUs so that they will read the oxygen level in the air(to fool the ECUs into a lean read) the engine runs at about 12:1 at idle and steady state throttle, of course the engine runs a little stronger and smoother BUT (after all that blathering) when I take temp readings of the headers pipes(all 8), about an inch away from the head, the temps are quite a bit lower than when the 02s are in their spot and doing their job in the exhaust system.

    I also have an LM-1 that I use when rejetting vintage cars for the Colorado Grand. I have not tried what you have but your findings do not surprise me. When the O2 sensors are on line one has to remember they swing from full rich to full lean within their control range. When monitoring this with a data collection system, thermo probes in the exhaust flow near the heads there is a fair amount of unused fuel still burning in the headers themselves. It is not until I get the engine out of the O2 sensors control that I see steady state reading start to appear. Of course cam timing is a major contributor to what readings you will get testing this. More overlap dialed in the more pronounced the temp swing will be. I will try to duplicate your tests on my mule car and see if I can come up with an accurate answer to your question.



    After all that, my question is if we 355 owners just had the headers duplicated in a far better material (not so much a custom design to make better power as Bruce would like) the heat this motor produces shouldn't bother them, correct?.


    The material composition is key to making the headers themselves live a long life. The design changes we have been discussing are key to the longevity of the engine and all of the other components as well as possibly picking up some torque along the way. Bruce's focus is not just a power gain. We are discussing 3 different systems to cover all the bases. I personally have come to the conclution that there is not a one design that fits all applications. There are a few that require an OE style replacement, some will want a new design that addresses all of these issues discussed and a few will want a full race system. My focus is on the 2nd of the 3 as I see this to be the most needed. I want a system that is fully emissions compliant using HyperFlow cats and a muffler of ones choice. Dealing with the exhaust reversion, incredible exhaust temps, etc and making it live the life of the car with no other ill effects is quite a quest. Surely everyone knows that once the final design is established and fully tested to be found perfect for the application the Feds will step in and say NO WAY! I figure we can work around that issue when the time comes.


    I guess we all have come to the conclusion that heat is what is destroying the headers(combination of the shields, cats, bypass valve and air pump). My factory headers still seem to be fine but I don't have any of the previously mentioned heat traps on my engine and the headers are ceramic coated. Just a side note, my right side header when the car was raced only had 6500 miles on it when it had to be replaced and there were holes in every tube the left side is still the original and appears to fine. I am not sure it would be if it still had all the heat traps connected to it.


    There is a fine ballancing act here. Remove the heat shields and the exhaust flow slows dramaticly due to the gases cooling and slowing down. The engine compartment temps sky rocket, ancellary components start to fail due to the added heat BUT the headers live longer. The heat shielding of the headers is a highly critical issue in the design, not just for the headers sake but the operating enviroment of the engine as a whole. Take that a step further and all of the heat shields in the engine bay are marginal at best and have all been redesigned and are being tested. There are a very few header coatings that will stand up to the heat generated in an emissions compliant 355. Even when those are used I found the radiated heat is still an issue. I have found the heat shielding best serving the requirements to be that used by Tubi.
    My next stumbling block I am dealing with is price. Once I have a design idea in mind that will solve 75-80% of the issues I have identified as ones that need attention one has to come up with a plan that is cost effective to the average owner.
    Headers are only one facet of the issues we are dealing with. As stated earlier by Bruce, the exhaust reversion is throwing some curves into the equation. Find a suitable replacement for the guides, liners, pistons, etc... and then one has to question if we are dealing with the chicken or the egg. What caused the failure in the first place? Was the guide material too soft for the application or was it a factor of the erroding headers coupled with an exhaust reversion adding heat and an abrasive to the mix, a combination of all the above or something we have not thought of yet?
    The final solution can only come once everything is understood, hence the importance of Bruce's statement:
    "NO ONE IS EVER GOING TO LOOK FOR something they NEVER considered possible."



    On another note, if in fact the 355 is ingesting bits of metal from the header than that is probably the reason there has been some liner failures(I'm still leaning on the cheap materials theory but then what the hell do I know). Regards, Vern


    Yup, thats my latest theory that I am fighting the urge to believe. I am in the process of trying to disprove my latest ideas now so I can take SOMETHING, ANYTHING as a constant and work from there. I too wanted to believe the cheap materials idea but am strongly leaning away from that now. I have yet to see any proof that this is the cause and have actually seen some examples that lean towards suggesting the opposite.

    Now a question for you. Why is it the right header is the first to fail? I have seen failures better than 2 to 1 of the right vs the left. Just another piece of the puzzle.

    Dave
     
  18. davehelms

    davehelms F1 Rookie

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    #168 davehelms, Aug 23, 2007
    I dont think it is the O2's, they just dont have enough swing to produce the effects I am seeing. I am thinking more on the line of the exhaust design and the cams.

    Keeping to the cost effective thought, we cant do anything with the cams, head design, etc.... so we are looking at the exhaust to fix more issues than getting fumes to the tail pipe. Once again the excerise in compromise. What is good enough?

    Dave
     
  19. bcwawright

    bcwawright F1 Veteran

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    #169 bcwawright, Aug 23, 2007
    About 2 months ago on another thread,Vern indicated this right side header deteoration.....Dave, I asked the same question. WHY?
    I find Verns data VERY interesting.

    I would like to express some thoughts here, and some questions also. What follows is my observations and data from prior RACE engine developement:

    1. On the same engine, running identical fuel, what effects egt's is cam timing and ignition timing. I never use anything but an heat sensor probe inserted directly into the exhaust gas stream, usually no more than 2"s from the head exh. port. At times I have even gone as far as measuring egt's all the way out, i.e. exhaust port,collector, and finally the exit point(tail pipe).

    2. I would expect some minor variations in egt's between cylinders on the same bank, but would expect there to be even closer numbers(average) when comparing right and left banks. If we are looking at numbers that are not close, then something is defintely "rotten in Denmark", and it ain't the cheese..lol

    3. The term "stoichiometric(AFR 14.7/1)" is a clean word for EPA, but a curse word for a high performance NA engine using a radical cam configuration. Our last 355 street engine dyno run using a WBO2 sensor showed an 11.2-11.3/1 AFR at full power under load. This was perdicted before the run, and factual data confirmed.

    4. EGT's are the first place to look(IMO) when trying to determine right vs left header degredation. Higher temps on one bank are important to me, especially if they are near the thermal limits of the header metal. An oversimplified 1st grade example is H20(water).....you can bring the temps of water up to a certain point and it still remains a liquid....add just a little more heat(i.e. a few degrees) and it turns into a gas.

    5. If egt's between cylinder banks are pretty dang close, wouldn't the next step involve looking to see if the flow rates from header to tailpipe are the same? I have always found that VELOCITY is the name of the game with exhausts. Velocity is directly related to heat.....as long as you can keep the heat in the exhaust the stream is linear.....as heat is lost the gas slows, and when it slows it begins to tumble. This tumbling produces "back pressure"(ANYTHING that permits the gas to lose heat)...I liken it to a busy congested freeway where cars stop and go,i.e. the accordian effect. The key here is to keep the exhaust gases hot without degrading the exhaust proper, and to keep radiated heat into the engine bay to an absolute minimum.

    6. I am lost on this Bosch Motronic EMS set-up. It appears to me that when the by-pass exh. system becomes active the O2 sensors' data is useless.....I cannot see how a "narrow band" sensor can detect a 11.3/1 AFR which we recorded.

    7. I am also not sure how the 2.7 or 5.2 look at the right and left banks. Example: 5.2 uses single MAF data for all 8 cylinders...are all 8 cylinders getting the same intake air flow? If not, does the EMS just assume this and compensates/adjusts per bank and not per cylinder? If one injector is faulty and let's say spraying too much fuel in that cylinder and this overfueling is detected by O2 which relays to ECU....does ECU adjust that one faulty injector or does it overcompensate for the one by also changing the 3 that WERE operating properly?
    Hell, I'm confusing myself with this!!.....lol.

    Verns 355CH is the perfect test bed(much less restictive exhaust system) to test these assumptions on. With his data we can then proceed to the street cars.

    TIA Vern for any data and your comments/opinions.


    Enough for now. I need a Zannex!!!!!!!!..
     
  20. bcwawright

    bcwawright F1 Veteran

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    #170 bcwawright, Aug 23, 2007
    After reading over Verns post several times, I found his comments concerning the cylinder liner issues to be profound. It made me stop and think....that "as we stumble around in the dark trying to find cause and effect of the valve guide issue(one of the key topics of this thread), we may in fact uncover some of the reasons why non-topic issues are failing". That to me is exciting, and should be great news to owners and repair shops.

    Thanks Vern, for bringing this to light.
     
  21. gothspeed

    gothspeed F1 World Champ

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    #171 gothspeed, Aug 23, 2007
    .................. I no longer have the desire to perpetuate this inanity :eek:........... you are "louder" than I ...... ;)

    ........................................hopefully, now onto the great tech discusion....... :)
     
  22. Llenroc

    Llenroc F1 Rookie
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    #172 Llenroc, Aug 23, 2007
    Hi Dave, This problem was exactly what I was trying to resolve a few years ago when I Replaced my RH header. I only replaced the one for 2 reasons it was cheaper and the other side was fine except for some very minor deformities in 2 of the tubes not enough in my opinion to replace quite yet but maybe do an experiment to see what happens over time. I removed the shielding on both sides (particularly in the beginning with the thought.. because it looks so damn cool, those unshielded pipes) and had them ceramic coated, remember one has(L.H) 6500 race miles on it no cracks but a few minor deformities and one is brand new (RH) I also insulated the alt. and brake lines below the headers and the fuel lines on the LH side of the engine and replaced the heat shield on the oil tank with a bigger one. I now have 13,000 miles on this experiment and absolutely no change in either header. I would have thought the LH header would continue to deform or crack or something(using the cramic coating as a guide for cracks etc.) but nothing has changed. Although again there are no heat traps on this system. I watch my engine compartment very closely to be sure nothing is being effected by the heat. The heat in a 355 engine compartment has so many avenues to excape ie; engine fans pushing it out, the hood itself, the challenge grill I can't think of anyother car that has as well of a ventilated engine compartment.

    Anyway on to the question, when I checked the temps with a Laser thermometer with engine running at a steady 2000, I know this isn't ideal, but I was just looking for a general concept. Was the RH side running hotter than the other? Individual tubes were about the same temp on each bank but the LH tubes were cooler than the RH tubes by about 250 degrees. I remember asking Brian about this( a few years back) and he suggested the valve timing would probably cause this. Could the timing from the factory set(a reason to very precise on cam timing and not rely on the factory marks to be correct) be far enough off on the RH side and with the combination of the lean burn(EPAs glorious 14.7:1) at steady state throttle and poor material be our cause of one side going faster than the other. Because of the poor material used LH will go at sometime too but not as fast. As you were saying before it seems to be mutiple causes not just a single one. I still lean on the material first but it appears that I have figured out how to make the factory headers work BUT my situation is unique and will not work for the other 99% of the 355s. ie; you have do deal with compliant cars, cats & air pumps etc.

    Now a question for you. Why is it the right header is the first to fail? I have seen failures better than 2 to 1 of the right vs the left. Just another piece of the puzzle.

    Dave[/QUOTE]
     
  23. Llenroc

    Llenroc F1 Rookie
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    #173 Llenroc, Aug 23, 2007
    Hi Bruce, I'm with ya on that Zannex thang my head hurts with this and I also hate to type, have hard time typing what I'm thinking. anyway my thoughts on your 6 and 7. And I think you are correct on your No. 4 I need a more accurate way of doing that.
    The 02 sensors on the 2.7 don't effect the exhaust valve, it opens at about 3500 rpm by other means. the info from the 02 sensors on the 2.7 is only used at idle and steady state throttle positions. The fuel maps in the ECU handle the fuel needed by the engine based on load, rpm, temp etc. the 02s job is to fine tune the mixture to 14.7;1 at idle and steady state throttle. My engine runs fine with 02s pulled from their postions. I leave them connected to the ECUs so they will "read the air" and fool the ECU into a lean reading. When I do this and read the exhaust the engine is running around 12:1 at idle and steady state throttle ie; it is running on the fuel maps only and not being fine tuned by the 02 sensors. Of course you would NEVER do this on a cat equiped engine because you would destroy the cats.

    The 2.7 cars can look at both banks indivdually because there are 2 unconnnected system on those 355s. The 5.2 cars use a single set of sensors and single ECU neither system can look at individual cyclinders. They way I understand the 2 systems is that the air flow meters are the main info source for the how much air and fuel, not the timeing of it or the ignition of it just the amount of it, with the 02 sensors playing a more active roll in contoling the mixture to that illustious 14.7:1 ratio
    You probably already know all this but when reading your post I just start thinnking out loud or is that typing out loud.. I don't know. Regards, Vern
     
  24. Llenroc

    Llenroc F1 Rookie
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    #174 Llenroc, Aug 23, 2007
    That was kind of my point awhile back its hard to stay on one point here because it appears that they are all related and you start to drift from one to the other trying to figure out why liners(more rare) guides and headers go bad. I know I shouldn't be so norrow minded on this but I still think it is bad materials more than anything. Brian Crall got me thinking about this a few years back and doing research here on topics dealing with the problems how and when etc. and also my own experiance with my car and having a complete service history on that car has brought me to that conclusion but of course that needs to proved by others as well. It would be interesting to look at the service histories of all of the challenge cars to an excellerated wear pattern ie; how many liner problems at what mileage, how many guide problems and when etc.

    Hey Dave what kind of records do you have on Challenge cars?
     
  25. Llenroc

    Llenroc F1 Rookie
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    #175 Llenroc, Aug 23, 2007
    Its to bad that this appears to true.


    Oh and drop the screwdriver and step away from the wall socket. I remember doing that one time(you don't gotta tell me twice) when I was about 5 or 6... Man was that cool. hahaha
     
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