PSA 1.6 16v engine problem

[FACTOR_LAMBDA]

Hello
I am modifying an engine Peugeot / Citroen. An engine of Peugeot 206 1.6 16v.
Data:
stroke 82 mm, diameter 78.5 , length con rod 133.5 mm
cams 280º, lift valve 10.15 mm , in 32-68,ex 70-30, 108 -110 full lift
Pistons : 12.2 compresion ratio
Cylinder head modify, 120 cfm inlet 10.15 mm no manifold(, with manifold 108 cfm ), ex 93 cfm with manifold.

Problem?

spark plug melted

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spark plug melted

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pistons

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combustion chamber

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The engine, the spark plugs melted.Measured power 125 hp + -. Lambda measured is indiferent, engine power is indifferent to lambda.

lambda measure (sorry for colour)

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power and lambda (sorry for colour) lambda completely diferent , power exact ????

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Testing on the dyno , diferent lambda, diferent ignition advance, diferent temperature ,always get the same result.
spark plugs always white.(lambda 10 -1, plugs wite , ¿?)
Dyno and lambda revised, is correct. Ecu Magnetti marelli revised, is correct. Injectors and fuel pressure is correct. (injectors news) pump fuel new. Exaust sistem original, no modified. Inlet manifold original, throttle mechanical.
The engine is new, rings, pistons, etc etc
I dismounted the cylinder head, and found.
Gasket cylinder head incorrect, 0.5 mm thickness, the correct 1.3 mm. , compresion ratio 12.9 a 1 but I also found the admission duct BLACK , exactly equal to the exhaust. Inlet BLACK , EXHAUST BLACK.
I do not understand this effect, excess of compression ratio, can cause this?

inlet duct

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Revised valves, possible losses. Valves is correct.
Why this black intake pipe?
Thanks for the help.

[WhizzMan]

What heat range spark plug have you tried? Can you test oil and coolant temperatures as well? How long does it take for the plugs to melt? What type/brand plug have you tried?

[FACTOR_LAMBDA]

What heat range spark plug have you tried?

Spark plug Bosch FR8SE0 , 5 dyno test melted, NGK PLFR5A11 no melted, but always white!! different lambda, injectors.... always white!!!¿?
Coolant temperatures? range 85º to 90º
Only problem detected, compression ratio 12.9 to 1
Low Power, sparck plug melted, inlet duct black, not respond to the ignition advance and diferent lambda....

All for compression ratio Wrong?

[nabihelosta]

Hello

I may not be experienced with PSA engines (at all), but something caught my eye here:

Heat range: Bosch 8 , NGK 5.

It is really very hot plugs, even for a stock modern road engine.

With 12.9:1, I will start by trying the NGK 8 heat range, then go one step colder too (9). Forget about Bosch, they have no place in such engines.

What is you costant A/F from say 5000rpm towards the redline, on WOT? How is your ignition mapped? What fuel are you using? (octane number?)

Thank you

Nabih

[FACTOR_LAMBDA]

I use fuel ,98 octane .
The ignition advance is totally indifferent. Same power, and the same lambda with different ignition advance. No react .
Engine react to the delay ignition advance ¿?¿?
Incorrect spark plugs never did these symptoms in other engines.First engine with these symptoms.

[WhizzMan]

If you have pre-ignition due to very hot spark plugs, you will not have any effect from changing ignition timing. Also, with fuel 98 and this compression ratio, you may have knocking/pre-ignition. Putting in a thicker head gasket like you already said you would do, should help there. The black soot in your inlet could be blow-back due to bad fuel burning and misfires or pre-ignition.

As nabihelosta already suggested, I would use much colder plugs to test with. As long as your plugs don't foul, you should be okay, at least for testing. With an engine in this state of tune, I would personally look at iridium or platinum plugs, but opinions vary on that. Start with very moderate ignition advance, 25 degrees on full throttle or even 20 and go from there, get your mixture and spark quality right first, before you tune ignition advance.

[nabihelosta]

Whizzman made some great points here. Thank you.

Did you ever do a static compression test on this engine? How much PSI on each cylinder?

My experience with BMW engines suggests that you may need higher octane race fuel on anything over 12:1CR.

By the way, with such a high compression, your exhaust system has to be extensively modified. Definitely it will never work, and create huge back pressure and heat in your chamber.

Thank you

[Guy Croft]

An engine with such a high CR should be on race-grade plugs. A quick email to me would have located these from NGK Race Division. That is one reason I am here. I am an agent and have access to their technical section. Let me illustrate: some of the plugs I buy are over £30 each. They are completely different to road-car plugs and yes, need to be. I don't understand why a long projected-nose plug like that is being used in a 16v unit, the nose will just pick up tons of heat. Some good points have been made already by members - well-done. I like the ones referring to pre-ignition induced by spark plugs running too hot and the last about the exhaust manifold which brings me on to my next point.

We're looking at a 'combustion event' as it's called. I wonder if the piston dome in your picture is scorched by detonation? Sure the head is covered in carbon and oil but that is not contributory cause because it has not been burned in the 'event'.

Here are some suggestions by me of possible causes:

1. If the ex manifold design is no good: tight bends, pipes too short or too small. High static back-pressure and adverse wave action: the pressure waves from one firing cylinder get into another cylinder. This upsets the firing cycle in a completely random way. So much so that the engine is actually impossible to calibrate. Strange but true. Why? Because you are reading Lambda from all four cylinders to calibrate the fuelling and ignition but actually each cylinder is getting random variations in charge density and cylinder temperature because of exhaust gas contamination. You think you have calibrated it right but the engine is actually 'doing its own thing'. Only sensitive exhaust gas temperature (EGT) in the primary pipes can give you a idea of what is going on. Turbo engines suffer terribly from this because of the high gas temperature and thus high wave speed. This kind of thing does lead to contamination of the inlet ports with exhaust gas because the stuff flows right across the top of the cylinder on overlap.

2. If the exhaust manifold is a good one then the cause could simply be detonation - too much advance/plugs too hot/intake air temperature too hot/fuel octane too low. Detonation may have damaged the rings and ring lands and that may be why your chamber is covered in oil.

3. The valves may not be seating properly. And if they were OK at start they may have suffered chronic contamination of the valve-seat sealing area due to running too rich. The effect of this is much like (1) above where gas can flow into the cylinder.If an exhaust valve loses its contact face it's pretty serious because then burning hot gas flows past the valve instead of waiting till the end of the firing stroke and it can melt the valve & seat.

A combustion event is one of the hardest things to diagnose, by the way. All we know for sure (literally) is that a plug has melted because of some extreme imposed on it (which even a race plug could not withstand) or the plug go so hot it melted on its own.

GC

[FACTOR_LAMBDA]

Thank you very much for the help.

This engine will not let me sleep.

1. If the ex manifold design is no good:

Ex manifold is original. In the flowbench several test , 90 cfm or anything else .Apparently is correct.

ex manifold original

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2. If the exhaust manifold is a good one then the cause could simply be detonation - too much advance/plugs too hot/intake air temperature too hot/fuel octane too low. Detonation may have damaged the rings and ring lands and that may be why your chamber is covered in oil.

Advance ignition ,is indifferent. Never saw this before. The ignition system is double coil. Ecu magnetti marelli. The engine runs much progress (50 °) as well as with little progress. (0 º) Is indiferent. ¿?
Plugs are very hot, But can a hot spark plug cause this?I never saw this effect as exaggerated.
20 minuts heat engine or 950 rpm (+-), 4 dyno test , plugs melted. Too fast, is not it?. I am totally surprised
Fuel octane?? Fuel commercial, 98 oct.
Valve seat reviewed, all right.

Compresion ratio recommended by the manufacturer of the pistons , is 12.2 -1 This engine has exactly 12.89-1.
Same engine get 140cv , with original pistons, and cylinder head original . and compresion ratio 11.5-1 and cams , ecu , injectors ... modified.

Now 120 cv
This engine is a serious problem.

Thank you

[WhizzMan]

The right static compression factor should be determined from the opening and closing times of the valve train, not from the recommendation of the piston manufacturer. Given the timing you give for your cams, I am guessing they are meant to be using higher compression than standard pistons, but to make an accurate judgement, you should have the full cam profile available and not just the numbers you are giving now. Each manufacturer has his own way of determining these numbers and the length of the ramp start and landing zone can add a lot of degrees to a number without actually contributing much to the flow of a cam. Did you do a static compression test with a good compression tester? What numbers did it give you (psi/atm)?

Your exhaust manifold looks pretty good for a stock one, but if you want to get more than the 140bhp out of your engine that you were already getting, you will need a much longer primary section, with a bigger inside diameter. At the flow rates you will need for that sort of power, this exhaust will be restrictive. Don't think that "flow numbers" have much influence here, it's all about high speed pulses, resonances and not much about static flow in the primary section. I'm sure Guy can give you some indications as to what diameter and how long and what inner diameter your primary (4) secondary (2) an end (1) sections of your exhaust should be.

Yes, too hot plugs can cause this, but most likely, you are running a combination of too much compression, too hot plugs and a too restrictive exhaust. They all add up making things go wrong very rapidly. Try colder plugs and as Guy suggests, get racing plugs.

Guy mentioned your piston rings may be damaged as well. That's a very good point, I would take them out for inspection before putting the engine back together again if I were you.

[Urbancamo]

After quick calculation, you are currently running 10:1 dynamic compression ratio. I think that's way too much even for this 16-valve engine and normal fuel.
With 12.2 static it drops to 9.45:1.

[Guy Croft]

You are running 60 deg of cam overlap - I think the ex manifold is one of the most serious problems you have. I say one because it may not be fundamental but in changing it to a more 'optimised' layout you can 'rule it out' as probable cause which you most definitely cannot at present. I would expect, with that kind of overlap and the very high cylinder pressure and temperature that 12/1 CR will generate, that the ex manifold will permit a very high and dangerous level of cylinder-cylinder interference. I think this is why your engine is insensitive to ignition timing. High CR compresses the charge more effectively than a lower figure and less advance would tend to be needed for optimum power. The same is true of an engine with high volumetric efficiency. I think your engine is suffering such dramatic & localised in-cylinder overheating that once it is started up you could probably run it without an ignition system at all.

I recommend that you strip the cranckcase down without delay to inspect bores and rings, and get a tubular ex manifold (header) made to this configuration:

Primary pipes - bore equivalent to ex port area length from head face to collector 24-27"
Secondary pipes - bore 25% bigger on diameter than primary, length from collector exit to next collector entry 7-9"

The collectors are not included in the pipe length (which is the chord length) and they should have a 14 deg internal taper.

The tailpipe should be same bore as primary. The silencer (muffler) must be of large volume straight thru perforated steel liner about 0.25" bigger on radius than tailpipe. The volume is that of the casing. Do not use two silencers if one will do the job. The bigger the volume the quieter it will be.

You have not shown me the intake setup/fuel system but be aware that with such a high CR (nothing wrong with it but still high in relative terms)if you are running a single throttle body rather than individual and separated runners with CR 12/1 (or so) with such a big intruder dome on the piston the chances of pre-ignition and/or detonation - to a greater or lesser extent - are very high.

GC

[FACTOR_LAMBDA]

Thanks for responding.
But now if I have a serious problem. Guy, your comment," change the exhaust system" .
This system exhaust is the approved for GrA ( FIA homologation sheet)
This engine , the car runs GrA. NO POSSIBILITY OF CHANGE EX MANIFOLD.
History Engine, first idea:
Cams 314 º
Four throttle bodies
Ex Manifold Kit Car ( FIA homologation)
Pistons forged

all discarded , car run in GRA.

Second idea:
CAms 280º , cam followers hydraulic
Cylinder head modified
and Pistons forjed GrA

This engine is easy (hitherto). Estimated power 150 hp.
If I can not change the exhaust, I have to put original pistons.

Same engine get 140cv , with original pistons, and cylinder head original . and compresion ratio 11.5-1 and cams , ecu , injectors ... modified.

This engine without modified cylinder head , equal cam ... 140cv. Just changing pistons and cylinder head modified,
all these problems.

[Guy Croft]

OK - just for a minute let us look at something else.

Have you personally measured the piston dome and combustion chamber volume to measure the CR? Or have you just read this from Wossner data?

GC

[FACTOR_LAMBDA]

I measure piston dome and combustion chamber.
It's the first thing I did.
Piston dome: 7,2 cc
Chamber: 38 cc
Cylinder head gasket: 2.48 cc ( 79.5 X 0.5 mm)
RC: 12.91 -1 , RC wossner theoretical 12.2
Cylinder head gasket incorrect, 0.5 mm . New gasket 1.3 mm New rc estimated 11.6.