The joys of a good service (tech. q's)

[tref]

My understanding of the oil is that the poor little molecules get mashed in the bearing... so after a while don't hold the pieces so far apart. The black stuff is carbon, which works rather well as an abraisive... With regards to the lighting a bonfire analagy, similar indeed, except you have ignored the time element...(it only has a short time to burn before the piston will be coming back up the bore anyway). Which is more likely to start the fire, and get it burning well with in so many minutes - one match, or the entire box?

 

[zcacogp]

Chaps,

I serviced the S2 at the weekend. New sumpful of GM's finest 10w40, new filter for the same, cleaned out the K&N, fitted the volvo distributor cap (see other thread.)

And, as always, it runs much much better. Only about 5,500 miles since it was last given new oil, but the overall difference is marked. It spins up better on the starter, starts more quickly, idles much more quietly, pulls more smoothly and harder, and I am sure it will return better MPG. (I'd also swear that it handles better, stops quicker and the radio sounds better, but I'm sure those are purely psychosomatic!)

But this sets a couple of questions up in my mind. The two big changes are new oil and a new dizzy cap. The old oil wasn't past it; it was dark in colour, but not treacly or overly thick, and it still seemed very 'slippery'. Neither did it have lumps of junk in it. What goes wrong with oil that makes it less good as a lubricant? Why does new oil, which appears physically very similar to the old in all but colour, do such a better job?

And the dizzy cap ... the old cap clearly worked - sparks were produced at the plugs, which caused the engine to run. The new cap will enable better sparks to be produced, but why do better sparks make an engine run better? The point of the spark is to ignite the fuel in the cylinder, so as long as the spark ignites the fuel and starts the process OK then why does a bigger spark produce a better burn? Figuratively speaking, if I am lighting a bonfire then I will get the same 'quality' of bonfire regardless of whether I light it with a small match or a blowtorch ... so why does a bigger spark improve the ignition in an engine?

Also, pushing that a stage further, if a bigger spark is a better bet (which it demonstratively is), will a bigger spark again be better again? Do fancy spark plug leads/'splitfire'-esque spark plugs/whizz-bang coils etc all improve the way that an engine runs? Or is it the snake-oil that it most people claim it is?


Oli.



Edited by Paul.S all done as requested Oli []

 

[ChasR]

As said, carbon can be abrasive, but the reason for why the car goes better with fresh oil is because oil loses its consistency as it is used. It thins down quite a bit unless you go for a fancy Ester Fully Synthetic oil (To give you an idea, Ford's 5W30 Semi breaks down to 0W20 after 5,000 miles). My Peugeot used to run better on fresh oil, and despite the hype of Fully Synthetics it ran much better on Total's 10W40 Quartz 7000 compared to Fuch's 10W40 and their 5W40 (both got dirtier quicker compared to the Total), and I gained about 60 miles straight away to the tank. To be fair it's what Peugeot recommended to put in. Dizzy cap is one of the first things I change on all of my Dizzy driven cars. My MGB that I used daily ran much better with the new cap even though the old one looked relatively new from starting to hesitation(pretty much disappeared). Whilst it helps the size of the spark it's to do with the insulation of the cap (shorting out due to the breakdown of the insulation) and the time at which it fires. Look up phasing angle in ignition systems and it should make a bit more sense to ignition sparks. As for plugs, a good OE spec plug is fine, but change it at the regular intervals and ensure the gap is correct.

 

[Copperman05]

I have often wondered the same thing myself, when I had my motorcycle there was an ignition upgrade available that apparently improved performance. I dont think it actually gave more HP but improved performace through more reliable engine ignition. An engine it seems is only as good as the ignition system that operates it. I guess that what you want in a perfect ignition system is a perfect spark every time, anything less and it affects performance, maybe not in a spluttering obvious misfiring sort of way, but if you have below optimum combustion in the cylinder then its going to affect performace somewhat. By hey, what would I know... Edd

 

[mr brightside]

If you think of the spark thing as an input and output of energy, due to the fact energy cannot be created or lost just converted from one form to another, a bigger more energy rich spark may result in a more energy rich combustion explosion. Anyone agree?

 

[tref]

Er, no... the spark is just a catalyst for the release of the potential energy in the fuel/air mixture.. The result you are descibing is right, but not how it occurs. The quality of the spark ensures that the flame develops through-out the combustion area. If it takes a while to ignite all the mixture (ignition of any given area of gas occurs from teh ignited gas around it, rather than directly from the plug), it is possible for incomplete combustion to occur. This is ensure by a number of factors - keeping revs low is one way, a combustion chamber on which the flame front can spread effectively is another (compromised by the shape necessary to get the mixture in and out)... and some engines ensure it by having a twin spark arrangement - using the bonfire analagy - starting it on both sides at the same time. I believe Jon Mitchell had some ideas, or had done some trials of this on a 944 engine.

 

[mr brightside]

Where does the energy from the spark go then? It has to be passed on in the form of the ignition of a cirtain volume of mixture. The weaker the spark the smaller its surface area so to speak so, as you said in your last post, the longer it will take for ignition to spread due to a smaller initial fire. I disagree the spark is a catalyst, a catalyst speeds up the rate of a chemical reaction but is not itself an initiator. Nitrous oxide is a catalyst sort of due to its addition of more oxygen which facilitates the addition of more fuel resulting in a bigger bang.

 

[zcacogp]

I don't think that a spark is a catalyst, it is an initiator. My original question was why a bigger initiator leads to a better reaction. The size of the initiator shouldn't have a bearing on the completeness, size or 'quality' of the reaction. Once the reaction is started then the size of the spark which started it should be immaterial. (But Nitrous isn't a catalyst either. Nitrous breaks down into nitrogen and oxygen at high temperatures, so adding nitrous to an engine means that you have a surplus of oxygen in the cylinder. This means you can add more fuel, which means more power. Effectively, the stoichiometric ratio which determines what proportion of the cylinder capacity can be fuel can be changed by permitting complete burning of more fuel. And burning of more fuel = more power, put simply. Where's Brett when you need him, eh?) Oli. ETA: The amount of energy in the spark is miniscule compared to the amount of energy in the fuel charge. A bigger spark means only fractionally more energy going into the cylinder, so I don't think this can be relevant. Interesting idea tho'.

 

[sawood12]

Potential energy is what you get between the cathode and anode of the spark plug. When that potential energy (i.e. voltage in this case) becomes great enough it creates plasma between the two terminals which is very hot. The energy is therefore converted from potential energy to heat energy which then dissipates in the cylinder. The heat clearly ignights the air fuel mixture and the heat of the spark dissabpates and adds to the overall energy, but it is a very very small amount compared with the energy released by the burning air/fuel mixture - fractions of a % of the total energy. This is because a spark is of very short duration and happens over a short distance so it has high energy density, but in actual fact is not a particularly large amount of energy. A stronger spark will only create better combustion relative to a weak spark. There is not a large amount of time for the combustion process to happen in an engine so a strong spark will get things burning more quickly and result in more of the air/fuel mix being burned and hence a better running engine. But there comes a point where a larger and larger spark returns no further improvement, because you simply run out of time for the entire air/fuel mixture to be burned no matter how large the spark. I think the feeling that the car runs better following a service is mostly phychological. I used to think that servicing the car made it run noticably better when I did my own servicing. Now my specialist does the servicing I don't really notice any real difference.

 

[mr brightside]

ORIGINAL: zcacogp (But Nitrous isn't a catalyst either. Nitrous breaks down into nitrogen and oxygen at high temperatures, so adding nitrous to an engine means that you have a surplus of oxygen in the cylinder. This means you can add more fuel, which means more power. Effectively, the stoichiometric ratio which determines what proportion of the cylinder capacity can be fuel can be changed by permitting complete burning of more fuel. And burning of more fuel = more power, put simply. Where's Brett when you need him, eh?)

Yeah sorry NOS was a bad example there i was just trying to differentiate between a catalyst and an initiator. Everything you have both said after my last post i agree with entirely, i wasn't suggesting the increase in energy from a good spark and a bigger bang were proportional to one another just that more energy on one side of the equals sign means more energy on the other, figuratively speaking. Sort of...spark=25bang, 2spark=50bang, 3spark=75bang Is this making any sense or am i just complicating the thing unnecessarily?

 

[dirtydirtyharry]

ETA: Some half-wit managed to mis-spell "service" in the thread title ... could some kindly mod correct it - thanks! (If aforementioned kindly mod could also remove this message then the half-wits' mistake could escape notice altogether! Thanks again!) Edited by Paul.S Title done. Couldn't quite manage to take out the admission of half-wittedness []

[][][] How cruel! [][][]

 

[mr brightside]

This thread seems to have ignited some interest in changing all my HT components, never been done as long as i've had the car so they're probably exhausted. If any of you bright sparks know where i can get a good deal then feel free to points me in the right direction in advance, it may lead to more power.

 

[zcacogp]

In turn ... MrB, That makes good sense in that the bigger the spark the better the burn. And it may be a linear equation such as you described. The bit that I struggled with was the idea that the energy in the spark is somehow contributing to the energy released in the ignition of the fuel/air mix, and an increase in spark energy of x joules would cause an increase in energy released in the ignition of x joules. I don't think that's how it works. Scott's explanation about a plasma field being created by the spark plug is the best I have yet read, so thanks Scott. It also explains why there is a theoretical maximum gain to be produced from the spark, and once you have exceeded this point then there is no more gain to be made. dirtydirtyharry, yes, he's a git. But we love him. Not sure why![] MrB (again), in my experience of fault-finding, a LOT of car running problems are caused by faults on the ignition side, to the extent that I would almost say that if a car is running badly, start by ensuring that the whole of the ignition system is in good order, by manually checking every single part. I can't vouch for the improvement in the way my S2 runs from just changing the dizzy cap as I did it at the same time as changing the oil and filter, hence can't isolate the individual benefits. BUT given the slightly burned state of the old one it can only be a good thing. If yours hasn't been done within living memory then it may be a good idea. (With huge caveats!) ("Bright Sparks". Ha! I see what you did there! Very clever, sir, very droll. Very droll indeed. Ever considered a career on stage? I'd pay for a ticket, for sure.*) Oli. * - dirtydirtyharry, perhaps Mr Smiff isn't the only git around here, eh? []

 

[tref]

Bert Gear is your friend for parts like this... he does a service kit which includes all the usual stuff, and then I guess dizzy cap and rotor arm on top. I have always considered dizzy cap and rotor arm to be service items, and whilst I generally agree with Scott, and haven't noticed a dramatic improvement in performance for servicing, I have noticed a marked improvement in mpg...for a while...(5%?)

 

[mr brightside]

ORIGINAL: zcacogp The bit that I struggled with was the idea that the energy in the spark is somehow contributing to the energy released in the ignition of the fuel/air mix, and an increase in spark energy of x joules would cause an increase in energy released in the ignition of x joules. I don't think that's how it works.

My understanding of it all only goes as far as BTEC Mechanical Science allows so i don't think i'm qualified to continue the discussion and will respectfully yeild, i'm a bit of a bookworm on the quiet (fact not fiction) so i'll keep my eyes peeled for some literature on the subject. I got a Haynes manual on fuel injection from a car boot for 2 quid not so long ago so i'll keep my eyes open for one on combustion theory if one exists. Cheers for the Bert tip Tref, i find their site intolerably difficult to use in some circumstances but lets see how i get on this time! Anything will be better than going back to Porschshop, although i do enjoy issuing threats of legal action to retailers...power to the people.

 

[tref]

I prefer to pick up the phone to Bert Gear, tell him what you are doing and ask him what you need - he'll always remember that extra stupid little bit like sump plug washer or the seal that goes around the bolt on the rockerbox. As for understanding combustion theory, I served a four year apprenticeship manufacturing engine components and testing in proper test cells... the only thing I learnt was how little we know. Twenty years latter I'm designing reactors, still trying to guess how they will behave, and still keeping my fingers crossed they hold together! Ka-boom.

 

[millimeep]

Back on the subject of ignition, electricity, especially the high voltage used for spark plugs, is notoriously lazy! The situation is this: every fraction of a second, you'll get thousands of volts appearing at the business end of the coil. Their only concern is getting back to earth and putting things back in equilibrium. Now, jumping across a spark plug gap, that's under high pressure as the engine is reaching peak compression is really hard work, so these cunning volts will look for any other way to escape along the way, so one source of problems is them leaking out of worn leads or caps. Another thing is if the gap between the rotor arm and the relevent plug output of the dizzy cap is too big, then the poor little volts get worn out jumping that too, and there's less energy where you want it, providing a big fat spark to get the ignition going properly. I've got a new dizzy cap/rotor arm to go on once I finally get the car together as mine were in shocking condition too! And thanks to mr brightside for packing his post with terrible puns []

 

[mr brightside]

ORIGINAL: millimeep And thanks to mr brightside for packing his post with terrible puns []

Yeah, all in a days work. Nice mixture of ideas in this thread.

 

[mr brightside]

ORIGINAL: tref Twenty years latter I'm designing reactors, still trying to guess how they will behave, and still keeping my fingers crossed they hold together! Ka-boom.

Interesting, i did my time at the old Allied Colloids (now Ciba S.C.) in Bradford before i was made redundant by Ciba's crack team of accountants. You'll probably remember their ka-boom incident in the early nineties when somene put an oxidising agent on the wrong isle in the warehouse, the resulting inferno was finally extinguished about 20 yards away from the Acrylonitrile tank farm; which is adjacent to the Acryamide tank farm and opposite the Methyl Chloride tank. Aparrently 10 ppm of any of those will render you dead as a dodo so it was a closer call than most of Bradford knows.

 

[tref]

Yeah, there are some corkers... a fire muster point next to chlorine storage in a certain water treatment works. Yeah? No, sorry, in the event of a fire, you'll find me on the M3... going quite fast... But to get it back on topic... everyone knows how much better it goes for polishing it... but why does it go better after vacuuming out the interior?