NefMoto

OK so I made quite a serious mistake somehow which has meant me sourcing a replacement block for my car, block is being shipped and I need to make sure that whatever the issue was it doesnt happen again. Car is a 2004 audi s4 with a pes g4 supercharger with a 7 psi pulley and supporting mods, bosch green 440cc injectors, devils own non progressive WMI running a single d03 nozzle pre charger. The car has been running as is for the last 10000km with no issues, I then went and had a couple of runs againest a new 3l supercharged s4 and the standing starts were a mess due to my clutch slipping, we then did a highway run from 3rd gear and once in 6th I lost power and saw smoke behind me slowly glided to the shoulder with the car stalling to the find the following the next day.

(http://i226.photobucket.com/albums/dd202/airtite/IMG-20130802-00037_zps37269aa0.jpg) (http://s226.photobucket.com/user/airtite/media/IMG-20130802-00037_zps37269aa0.jpg.html)

Now I can understand why a piston would melt BUT what doesnt make any sense is that the damage is ONLY on pistons 6,7,8 and only on the one bank, everything else is in perfect condition with no heat damage to either the piston crowns or head. Any ideas?

Were you logging AFR? Which bank gets fuel from the rail first?

I'd bet that bank was running lean.

holy snikeys i hope you werent using the pes tune bc there know for that

http://www.audiforums.com/forum/b5-models-69/can-i-turbo-my-v6-181979/page5/#post1386142

while I was tuning the afr on both banks was the same, that bank is the one furthest from the inlet into the fuel rail though..

nope not the PES tune BUT I am pretty sure I did something wrong in my tune to cause this. I am just trying to figure out why the rest of the pistons are fine and only the last 3 on the one bank...

You should have had a wideband installed in bank 2. You ran out of fuel and ran lean. It's no coincidence that the last 3 cylinders to get fuel were the ones that burnt up.

I would agree with you if the damage to the piston was more extensive ie in the center of the piston and not just on the intake side and bear in mind I had driven the car to red line lots more than just this one time over the last 10000km.

last logged run

(http://i226.photobucket.com/albums/dd202/airtite/8E0910560D_20130523_100433_zps87dbfb4a.png) (http://s226.photobucket.com/user/airtite/media/8E0910560D_20130523_100433_zps87dbfb4a.png.html)

How were you logging wideband?

these logs were from the lambda values

So the B6 s4 has wideband o2's. What pump were you running? What was it rated at? How many miles on it? Flow rate plummets as pressure increases, but I'm sure you know that.

stock pump, 4bar fpr... honestly it looks more like detonation at that edge of the piston more than running lean to me but if that was the case I would expect to find the same damage across the board but it just doesnt make sense that its only those last 3 pistons, which then lends credence to a fueling issue.

I think you should have been requesting more fuel anyway, but it's irrelevant for the conversation at hand.

PES blower with a smaller pulley (High IAT's, super inefficient, undersized for the 4.2 to begin with)
Stock fuel pump (I tuned a B6 S4 with a stage3 2.7T, stock pump couldn't keep up over 4500rpm, it went really lean)
High compression
Lack of proper monitoring

Everything that I see points to bank 2 being starved of fuel and running lean. This is a fairly common failure to see when the hardware's not right.

To battle IATs I had implemented the WMI and looking at the EGTs it didnt go above 825C, I agree about the blower being undersized for the 4.2 fair enough but like I said car was running really well up until this point with multiple runs right into the redline.

This is just my interpretation of the evidence provided. Unless you were logging when it happened, it's all just speculation anyway.

yup you are right, will just have to put it all back to together and do some more extensive logging to ensure I dont break it again...

The problem is your AFR request and that you never looked at your EGT's. This is running WAY to lean up top.
Req. lambda makes me cringe... leaner to redline, really?

I guess you have now learned from this, just there are a bit less costly ways to learn - such as picking up a book about forced induction motors :/

i have to agree with prj some, without having EGT sensor, those AFR's are kind of high, but you are running WMI, that picture looks like detonation, i had a failed spark plug cause detonation with proper fueling and the piston looked exactly the same.

edit: just noticed the rest of what i typed didn't go, how did the plugs look on the other bank?

That looks just like a Subaru with a cracked ring land.
Were the pistons even designed to handle what you are asking of them?

im not sure which post your talking about, but if it is mine, yes, this is a stock motor with a stock tune, 360 HP twin turbo engine, plug porcelain cracked causing hot spots.

I'm with everybody else, thats lean you need more fuel.

I was under the impression that 850C egt temp was well within safe limits?

prior to the failure, I had done a plug check on the last service and the plugs looked perfect, light tan color with absolutely no heat damage to the electrodes.

(http://i226.photobucket.com/albums/dd202/airtite/8E0910560D_20130523_100433_zps116589e8.png) (http://s226.photobucket.com/user/airtite/media/8E0910560D_20130523_100433_zps116589e8.png.html)

Is that during a 6th gear WOT pull? You won't really have EGT problems in 3rd gear.

yup 3rd gear.

Well I assume your EGTs were spiking way more than this during your 6th gear pull on the highway.

fair enough I never logged any 6th gear runs, surely if the EGTS were that high the damage would be on the exhaust side of the piston and not on the inlet side and if it was EGTs surely the damage would have been uniform across all pistons on not just those 3?

That is calculated EGT.
It's not actual EGT.
Did you measure your EGT using an actual probe and a gauge or not?

850C post turbo is close to 1000 before turbo on a turbocharged car, it's the limit. On a supercharged car 850C is probably ok depending on the location probed. Definitely OK in the exhaust runner. However, if this is from stock EGT model then this is at least 200 degrees off after supercharging it, so this perfectly explains what happened to your engine.

With high EGT it does not matter on which side the damage is, it's just going to let go at the weakest point. I don't see any serious det marks either.
As to all cylinders being damaged - not neccessarily. One side can run hotter than the other.

thanks PRJ, well like you said this has been a fairly expensive exercise but one that I have learnt quite a bit from. Will be a bit more cautious next time round. Block should be arriving next week and can start the rebuild.

Next time you are tuning it install actual EGT gauges, work on KFLBTS so that it keeps EGT's low.
And I would request richer LAMFA across the board as well, it should make more power at 0.82-0.84 than it does at 0.88, and then use BTS to go richer from there to keep EGT's down.

wish I had access to actual egt probes unfortunately with me being a hobbist I dont. I will apply what you say and see how things go.

You can buy it at a lot of places, then you only need a gauge for it, or just buy a kit.

Just an example: http://www.aemelectronics.com/egt-gauge-0-1800f-with-analog-face-772

Pistons almost always melt on the intake side... I'm assuming this would be due to a extremely hot cylinders igniting the incoming  fuel air.. From there it probably goes downhill fast... I would check fuel pressure after its all fixed but it looks more like a tune issue.... how do the other plugs look right now? I'm willing to bet those were hot also... Sucks.. I need to invest in better monitoring also but I'm relatively conservative with my fueling to avoid issues..

no heat damage to any of the other plugs in fact they all looked pretty oiled up after the failure.

hard to say :-\, if it were me i would tone the tune down after the rebuild and monitor fuel pressure when WOT

I would monitor both fuel pressure and real EGT's with a thermocouple(s), not relying on the modeled EGT values.  Also, a 3-gear pull from 3rd through 6 will result in much higher EGT's than 3rd alone. Even if you had real EGT values from previous 3rd gear logs, those wouldn't necessarily reflect the EGT in 6th gear after rowing through the gears.

OK rebuild done 500km under its belt and engine going strong, reverted to stock file just with changes for the 440cc injectors temin/tvub/krkte. 4th gear run logs attached any input advice on a "safer" approach to a tune for this car is welcome?

Stock tunes are generally lean no?  I'd at least enrich it!

This is the stock lamfa/bts. Enriching lamfa across the board so lowering all values by about 5%? and do teh same for bts as a starting point?

If it were me, I'd target an AFR of 11.5 until you know you can safely lean it out. In addition, I'd reduce timing at peak load and high RPM.

Yeah, take it really  conservatively, and make small adjustments.  Any updates?

I tried with lower bts and fueling and the car was horrible, I am busy having the blower rebuilt new bearings/seals/rotor coating etc which is taking a bit longer than normal.

That thing was just too lean.

With the right plugs / coils / etc it should chug right through an 11.5:1 or even 11:1 mixture without any issues. Hell, we're firing a 900 bhp bonneville 1.8t cylinder at those mixtures with stock coils, because we are concerned about exactly the kind of heat issue you had there. 40-42 psi and it doesn't misfire a bit.

Staying in it for minutes on end is FAR different from a thermal POV then just a few quick 3rd or even 4th gear rips.

Also, that doesn't look anything like knock to me- what's the quench pads on the head look like? Perfect probably...

I also vote for tuning it richer. You really are gaining nothing at all by being so lean. Some engines won't like being in the 10.x but that's really getting pretty damn rich anyways.