my roommate had been putting together a turbo kit for a while. once he had all the stuff together, i made the downpipe and the dumptube and i ran the oil lines for him and all that.
tuned it the same day that it was put on. i have a crome dealer license and used a gold bin.
started out with a basemap i found in the xenocron bin depo. it was super rich. after taking a bunch of fuel out i started seeing 15:1 in cruising cells. once the vacuum cells were where i wanted them we eased into boost and eventually got the afr's into the 11.0-11.4:1 range.
car had ngk bkr7e plugs gapped at .028". 93 octane. set timing with a timing light, while locked at 16 degrees btdc.
after tuning the car felt great. i was logging 10.5psi at wot @ redline. boost was holding steady, no creep. car good for a couple weeks and then started pluming smoke into the cabin after wot pulls. checked compression and found cylinder 4 was down to 120psi. pulled the head and found the piston melted..

timing was at 19.5 degrees in the 10.5lb column, which equates to .88 degrees retard per psi, conservative.
specs:
b18b1 170k miles
compression before turbo was good. i believe it was 175-180psi
drag manifold
tial 38mm gate
ebay 20g
ebay intercooler 30x12x3
ebay ssqv
dsm 450's with resistor box
2.5" downpipe and exhaust

thanks,
jack

 

almost 200 views and everyone is as lost as me?
somebody must have some insight

 

Stock pistons with 170K perhaps?

 

Did you examine the plugs to determine if they were all burning the same?
Using dirty old dsm injectors isn't exactly always a good idea.

 

That was my initial thought but I tuned the car that they were previously on and it ran fine for months until he parted out and my roommate bought them. But that kid was n/a
so idk..

 

I didn't personally check the plugs recently but he took them out himself at school (uti) and the teacher I guess said they looked good. For what that's worth lol
I checked them once right after the tune and they looked fine.

 

i would want to know what the plugs look like after the piston melted.

 

ill try and get him to bring them home. he went back home which is 2 states away

 

Were you logging boost via the stock map sensor and Crome? The stock sensor will only log up to ~10.2-10.5 psi.

Did you confirm the pressure it was running with a boost gauge or any other reference?

Like stated above.. it definitely could be a faulty or lazy injector.

 

yes it was on the stock map. i was cell tracing with the hulog and could playback the log and 10.5psi was the highest it saw.
also using a boost gauge by autometer that was reading about 9.5/10psi

 

the 10.8psi and 11.2psi columns were never touched.
but if your saying the stock map wouldnt read them anyways i guess thats why.
but the boost gauge said 9/10psi anyways..

 

yeah, the boost probably increased a bit on a colder day...and the fuel and timing at 13psi would be the same as the 10.5 column, if thats as high as it can read.

my rule of thumb, the map sensor needs to read at least 3 psi over the highest boost setting the customer wants to see

that way you dont find yourself in situations like this, and you can set a boost cut in the calibration

 

What if I said I had a boost cut set at 11.2 though? That's what it was at.

 

It never would've hit boost cut because the map sensor can't physically read that high.

Never set a boost cut higher than 9.5-10psi on a stock map sensor!

 

well thats a possibility then. i guess he wasnt paying much attention to the boost gauge.
he is buying a longblock LS and we will try it again. maybe have the injectors cleaned and tested too..

 

damn that seems retarded that crome wouldnt give me some kind of a warning. maybe i missed it somewhere... ive honestly never heard that. sounds like its pretty common knowledge though.

 

how likely is it that there is only damage to one piston? wouldnt that narrow it down to something with that one cylinder?

 

Not necessarily you are running boost on a stock cast piston that wasnt designed to see boost. While 10-11 psi doesnt seem like much on crappy gas, timing and whatever else this can really stress the piston. Most likely just melted due to too much ignition. Can't really tell unless we see the plugs. Seen this all too much on stock pistons. Just lower the boost to 6-8 and be done with it. Leave the tune very conservative. Also you can have too little timing and EGT temps can rise as well.

 

on your cam low ignition settings what is the timing set to in the boost section.
where do you have the v-tech engage and disengage.

 

It's a stock Ls there is no high cam..

 

boosting 5th gear?

 

i told him not too, but idk

 

Exactly, I usually set it at 9.5.

I also usually pull a bit of timing around 5000 rpm to help with peak pressures