Short story from a customer of mine:
B16a2 turbo, build, stock sleeves, JE 9:1 pistons, Garrett GT28rs running at max 18psi.
Because of overheating problems got a cracked nr2 and 3 sleeve.

Now the block is rebuild with darton sleeves and the rest stayed exactly the same. Even the pistons are the same.
The guy drove for 1000 miles with the old mapping without any problems and it was time to retune it (by me) and to put some more boost on it.

And then all disaster,
When we put it on the dyno we encountered quite so boost fluctuations. After a few runs around 19psi we had the boost pretty much under control (Apexi AFC-R) and made a base run. I made a log in eCtune from this run. It was running quite rich but further no problems.
Then we boosted a little more and made a run to see if we got what we wanted (21psi)
But halfway the run I saw the AF falling to 13,5 so I stopped the run and noticed it ran on 3 cilinders... Not good.....

After inspection the 4th plug was broken and we clearly had a sunk 4th sleeve. We also saw scratched walls on all cylinders!
Later we took the block apart and measured ring end gap en p2w clearance. All seemed ok and were not to tight.

Some pictures say it all:









A screenshot of the run before the breakdown:


It looks like the pistons over expanded or overheated. But how can this happen with this pig rich condition with these kind of timing?
Before tuning I checked the timing myself and it was almost dead on.

Who has any idea what happened here?

 

What was the p2w??

 

You said you checked the p2w and it was "OK" but you never stated what it was. Clearly it was not enough. Do you know what EGTs were on this engine?

 

possible washed cylinders from over fueling? Thats alot of scuffing so i agree as well with P2W being to tight....

 

don't let the bed bugs bite

 

I measured the p2w myself when we took the engine apart. All cylinders were more or less 0,0035.

 

 

explain?

 

10:1afr is way to rich....

 

.0035 is t00 tight.

where is goldilocks?

 

0,0035 is within JE specs. What is a good clearance in your opinion?

@non Vtec,
10:1 is certainly too rich. But normaly not a reason to give such damage.

 

I spent months on a CMM working with a NASCAR team and Wiseco pistons to improve the roundness of their pistons at operating temp and reduce the amount of material removed from the skirt. We found some interesting things most of which I cannot discuss here.

I can say that one of my old sets of JE pistons would not have come close to passing our tests for material loss on the skirts but we had a much smaller sample size (4 pistons) so it could have just been that set.

Many people have reported scuff with a .0035 ptw under boost. .005 is probably a better number but you can go even larger as long as you take care to let the engine get to operating temps before driving it around as there might be some slap.

My pistons scuffed just like yours and also were a .0035 ptw. However, that set of pistons had no evidence of detonation.

Where did you measure the PTW? .5" from bottom of the skirt?

 

Yes I measured .5" from the bottom.

Thanks for this answer. I never encountered such damage after a temporary rich condition like this. Maybe the engine builder should re consider his statement about his chosen ptw clearance.

 

No problem. It has been a while since I used JE pistons but I am pretty sure .0035 was recommended. Unfortunately after all these years it still looks like they haven't changed that recommendation. The damage was probably already well under way when you got to tuning it.

 

i have a set of je's in a built vg30dett i picked up. p2w was .0035 and they have mild scuff... gonna clean them up and put them back in a .005 as letting it warm up is a non issue for me.

 

Heat the pistons to operating temp, then remeasure them + check roundness?

 

that damage to the crown plus the major scuffing on the major thrust axis side makes me think these pistons are now paper weights
since the major thrust axis side has holes in it from the large amount of missing material

 

.0035 ptw. happened at about 417hp @7000 rpm on the dyno working my way up in the boost range on pump gas. it finished the pull ok, but i heard it making some noise when it came back down to idle. took it off the dyno right there and drove it home 30 miles. it was my first pull on 16 psi and afr was around 10.5:1. never got a chance to lean it out. there was no detonation



went to .0045 ptw. 475hp here's what they look like after about 3000 miles. they have some wear but really no vertical scoring

 

I would like to hope piston expansion has more to do with EGTs than HP. As Ive made more HP with less p2w before. BlackEG do you know what your EGTs were?

 

So is it safe to say that on a high hp high rpm built motor that p2w is acceptable at .005?

 

From my knowledge it's all down to power output (unless something isn't right). The more power you make the more heat you make...

 

eh to a point... EGT's are mostly controlled by fuel and timing... which remains pretty constant across the powerband in relation to air/fuel vs. power...

 

Rich thats an oxymoron to say its not EGTs but the more power you make the more heat lol.

Heat is heat. EGT = Heat = expansion.

 

Yeah but if the heat energy is been put into the exhaust then wouldn't the temperature inside the cylinders be lower? And vise versa....

 

the in cylinder temperature will always be higher unless timing is severely retarded, in which case combustion continues to occur in the exhaust manifold.
Turbos simply take that heated exhaust gas and convert it to mechanical work. the egt's pre-turbo are higher than those post-turbo due to the fact that turbos absorb the heat.