Melted piston...

Well. This is a long journey that started 2 years ago. I broke som oem piston on my N54B30 BMW engine. After 3 or 4 failures I built a new one with forged internals. This was chinese milled pistons. It worked. No more failures. When the engine was working I could go faster on the track and then the oil system was the limit.

I bought a S55B30 from the BMW M4 as I had read that it is an awsome oilsystem in this one. And it is indeed awsome. I have read about BMW factory cars with about 580hp and thats why I thought that my 600hp on E100 was no problem. But I melted the oem pistons quite fast. So... A new fully built S55 with JE pistons was built and I was pleased. This time I didn't have more than 580Hp because of some issues with the clutch.

But hey... Why not melt the JE pistons aswell... 😡 I really need help to understand. The teories has been bad fuel, too much timing, bad pistons and so on. Now the working theory is backpressure and maybe to small returnline on the fuel.

Any ideas??

I forgot... The egt is good. Aprox 850 celcius. And timing is not too much. I have had 4 different tuners with good knowledge of these engine take a look. I has been warm, but the egt is good. This is why I cant understand

I don't see how we are going to second guess "4 different tuners with good knowledge of these engine" -- but I'll try.

-- Have you monitored cylinder head temps? -- EGT may not be telling the whole story, and sustained EGT of 850c perhaps might be too high for the combustion chamber shape, and or piston material.

-- Have you tried colder plugs? Perhaps your spark is not what is igniting the mixture, and a glowing plug is leading to pre-ignition.

-- Have you tried surface coatings on the pistons to improve ability to withstand extreme temperatures.

-- Have you tried running richer to reduce combustion temperatures and reduce potential for detonation. Does this result in lower EGTs?

-- Are you running Knock Sensors -- any data / clues from that?

And have you checked your fuel injectors to see if they spray fuel evenly?

Where is the EGT being measured? Post turbo has had a fair amount of energy taken from the exhaust stream by the turbo.

E100 can also have issues with pre-ignition so this may be causing the damage to the pistons.

@David

Tanks, this is what I was hoping for. Some new input. Of course you shall second guess my 4 tuners. We may all miss something

I do not have cylinder temp. But from what we all can see, its way too high.

I have not tried colder plugs. This is with oem plugs. I think I got colder to the N54 when it didn´t melt. This is something I have thought about, but then forgot. tnx.

No surfacecoating.

Well, not richer. We have about 0.84 Lambda on load. It should be good. One of the tuners I have spoken too thought that the problem could be fuel that stays in the chamber and then burns slow on the piston. This is causing the piston to melt. The log shows that when I close the throttle the fuelpressure does not drop as fast as we want to. I used to have AN8 pressure and AN6 return. This is now replaced with AN8/AN8 and a new regulator.

No knok sensors yet, but soon.

@Georg

Yes, the injectors are good.

@Blackrex

The egt sensors is aprox 30mm from the exaustport.

We could see at one of the failures that I had a few spikes in the egt. First I thought that it was sensor fault, but it may also have been a detonation. I had one point at about 1100 celcius, but then back to 800-850. Those were probably detonation. But that was a test with the S55 angine and oem pistons. I accidently used the wong map. Thas was made with 9.0 compression and I hade switched to another engine with 10.2 compression. Så detonation was not impossible to say the least.

But after that I have not seen the spikes, I know this doesn´t meen it is not there, but less likley

There are a few things that you'll need to look at with your engine, those pistons do look melted rather than detonation damaged.

High ethanol-content fuels can suffer from pre-ignition so I would be looking at your plugs getting hot, your ignition timing being too far retarded or your injectors not spraying properly, all can melt pistons.

The spikes you're seeing in the EGTs will likely be pre-ignition. You need to remember that EGT sensors are quite slow in reacting compared to the speed at which the engine is moving, so the rise in the temperature you see for half a second has seen the engine spin hundreds of times or more.

How were your injectors tested? Generally, DI injector testing machines cannot supply enough pressure to get a full working pressure test.

What are your cam positions during the pulls? On boosted engines with smaller turbo's you can get a lot of EGR type events leading to higher in cylinder temperatures if the cam timing is wrong.

I have portinjection. DI is removed. I have not checked the cams, but the turbo is a Garrett G40-900, so not so small.

So youre saying that my plugs start to glow due to preignition? Sounds like something... The plugs are always melted. But what melts first, plug or piston. I am starting to think that the plug melts first... ?

If you haven't removed the DI injectors they can act as hot spots too, the tips melt over.

0.84lambda doesn't sound like thermal management territory for a port injected engine even on ethanol to me?

Detonation will result in cooler EGTs as the energy has has longer to dissipate into the piston, head and cylinder. Likewise if you end up with a near conventional burn from pre-ignition it should be cooler. Misfire or partial misfire burning into the exhaust stroke will be hotter.

Surely adding fuel to target closer to 800C would be a good starting point if you have dealt with the DI injector issues.

Henrik, how much more power did you get comparing to stock engine?

Just so you know NGK advises to go one step colder on spark plugs for every additional 50-100 hp- that would reduce combustion temperatures somewhat about 50 degrees C. If you kept original spark plugs it could be one of the reasons (I believe you have a combination of at least two reasons) why piston melted.

Tnx. The latest I had 130hp more

I have plugged the DI in the head. Its flat now

you're on port-only injection? what injectors are you using?

Yes Port only. Bosch Motorsport 1300cc

A thought... If the sparkplug glows, shouldn´t the hole in the piston be in the middle?

Not really. It works like a gas tourch - can be on intake or exhaust valves side depending on the engine.

From what has been said, it seems all the spark plugs melted their centre and side electrodes, but were all the pistons suffering from overheating and melting?

Many/most modern engines are designed to run at, or close to, stoich' and running power rich means a hotter burn - plus any other changes to increase the combustion temperatures. The spark plugs' also need to be 'warm' enough to prevent fouling at low load and rpm. this means that a standard heat range 'plug will tend to run very hot in a modified engine - as can be seen from the 'photo.

As has been suggested, at least one grade colder is a good idea and I'd suggest a couple of grades - there are also different centre and side electrode designs, and a recessed type with a colder side electrode path might be worth investing in.

The problem is that the electrode(s) can get hot enough that, with the heat of compression, the fuel-air around it can get hot enough to spontaneously ignite - same principle as glow plugs on model aircraft engines and the very early "hot tube" ignition used on IC engines before spark plugs were developed.

The probable reason the sides of the piston failed is a pressure spike, possibly igniting the mix at the edge of the piston, similar to classic detonation. It's possible it fractured a ring that then allowed hot gases down the side of the piston, rapidly melting away the aluminium.

The EGRs seem rather high, a possible reason is over retarded ignition timing used to compensate for poor fuel, too much mechanical or dynamic compression and/or boost. This may, in part, also be compromised by tuning around the pre-ignition a too-hot spark plag may trigger.

Oh, while the injectors may test out and be very close in flow, but the intake and/or exhaust manifolds may be allowing better cylinder filling/clearing than others, and those may be running leaner than the average - but that would mean some cylinders more affected than others.

Tnx Gord.

This sound like a good explanation as of what happened. All this discussion aswell. Historicly there had been different cylinders. I think that cyl 1and 5 is clear of faliure, but 2, 3, 4 and 6. This last time with the JE pistons the car started to missfire and I lost one cyl when getting out on the straight. I was cruising back to the pits and putting some small load on the engine just to see if it really was a lost cylinder. Then it blew... So probably a melted plug that then meltet the piston.

Time to get some new sparkplugs and rebuild once more...

just out of interest, are you still using the DI designed pistons?

These are designed to create a rich pocket below the spark plug and can cause lean edges around the rest of the cylinder. This is one of the reasons you can get LSPI (Super-knock) when running DI, I'm not sure how it would affect the dynamics running these pistons on a port injector

Yes, I have oem style pistons. I have been thinking about this aswell, but didn´t find any info that it should be wrong

do you have a map file and datalog you'd like to share?

I have several. Just got to get my Laptop from the workshop.

this is the latest failure from the pictures above. I tried attching the log, but it wount work. Here is a screenshot. The marker is where I guess the piston fries. If remebered right. Before that I had already lost one cylinder. The MAP should go up to 240Kpa at full throttle.