2 broken pistons. What caused this?

**kdowning** · 06-01-2014

Well the car is a 1999 GTP, 165k ish miles, zzp small pully and computer remap (not sure on size, was installed already when I bought car.) In December was leaving work at 2am and the temperature was 10 deg F. Car was warmed up 10-15 min before I left work. I drove around town before I went home for 5 or so min. (I live 1 mile from work and like to charge battery up good in winter before turning car off.) Was 2 blocks from my house and it started chugging and didnt have much power. I limped it home and when I pulled into the drive way thecheck engine light came on then I turned the car off. Checked fluids and belts and they were all good. Had car towed and inspected. They said at had a bent over plug electrode causing a miss fire and check engine light to turn on. Bore camera pitcures showed a piece of metal stuck to the head. They wanted $2k to pull heads and inspect and put all together with a used supercharger. (They were thinking supercharger went out and engine ate something.) I had them put it back in my driveway for me to look at when I get time. I bought a 2008 Grand Prix and let the 1999 sit.

This weekend I finally pulled heads off and found 2 bad pistons. Not sure what caused it but seems weird how both pistons look broken exactly the same. See pictures.

**ItHurtz** · 06-01-2014

To small of a pulley and not enough mods

**kdowning** · 06-01-2014

Trying to upload more pictures yet.

**Fivefingerdeathpunch** · 06-01-2014

Chipped pistons are cool.

Running a smaller pulley without exhaust mods is a great way to make the piston weaker and I guess they both just decided to chip.

**REDCRAPGP** · 06-01-2014

Yup small pulley and not enough mods to allow you to run said pulley without knock

**Scottydoggs** · 06-01-2014

good old small pulley, and no mods, aka KR and chip chip er roo.

it was a chunk of piston that smashed the spark plug.

you do use 91 octane or higher too right? 93 or higher is preferred if you can get it.

**ericspecullaas** · 06-01-2014

Thst sucks but you didnt have enough mods to support your "smaller" pulley. Untell you get headers, cam, ported heads and a tune dont even think about any pulley smaller than 3.8. It sucka you blew your motor but a simple question/reading will save you time and money.

**kdowning** · 06-01-2014

I cant get piston pictures to load but the piece that broke out was 1.5 inches by and .25 inches. Heads are not banged up and neither are the domes of the pistions. Its like a hammer knocked off the edge of the piston. It was on cylinders 3 and 5 i believe. I always ran 91 oct and sometimes 93 if they had it.

**ItHurtz** · 06-01-2014

91 on a smaller pulley with no headers... time for a new engine whoop

**Scottydoggs** · 06-01-2014

kinda like this?

find a used engine drop it in there. yours is a scrap now.

**Fivefingerdeathpunch** · 06-01-2014

The damage was done before you bought it, they just let go when you drove it.

The chip will break off and maybe hit once or twice and normally smack the plug tip and get sent out the exhaust valve right away.

They always look like this and the middle cylinders are prone to it.

**kdowning** · 06-01-2014

Just like that but on 2 pistons.

**kdowning** · 06-01-2014

I had the car 4 years and put on 50k miles on it. Looks like I am parting it out. The real big bummer is I put a rebulit GM transmission in it 2 years ago and that has about 18k miles on it. That will be fore sale.

**ItHurtz** · 06-01-2014

junkyard motor is $600 or under and you have a perfect running car again.....

**Scottydoggs** · 06-01-2014

drop a used engine in it and sell it off, you;ll get more for a running car vs parts. invest a little more to get it back.

**theaceofspades** · 06-01-2014

Yeah that's stupid to part it out. A JY motor could be cheaper than that.

**ericspecullaas** · 06-01-2014

Your going to sell your car for how much? Dont be a dumbass get a motor and get back up and running

**kdowning** · 06-01-2014

I was thinking about a used motor then sell it but the car is 2 hrs away from me. Thats the only place I can work on it. I'm just going to part what ever I can then junk the rest out.