Hi all,
Built engine blew after 300 miles of drive.
Vortech SC-trim with 928 impeller,
stock fuel rails, boost was 9 psi.
I have photos of one of the pistons. Note that two pistons were broken like the posted one, and all 6 have scratches in the interior side of the engine.
Pistons are Wiseco, 8.8 compression, 96mm.
I'm trying to find out what went wrong. Would be grateful to anyone who can point out to the possible cause, which I guess is possibly in the tune.

 

Wow, sorry for that! How many miles on motor?

 

. . .

afr, timing?

 

Saw that. I was asking TOTAL miles, not built miles ; )

 

60k miles before rebuild

 

did not have AFR. Trying to find out what breaks pistons..knock or lean?
during the tune it was some 11.6

 

I'm no expert, but that looks like maybe some pretty mean detonation (knock).

What are you tuning with?
Was the car tuned, or just on a base map?
Any datalog files?

 

sub'd ...

 

Sorry to hear, definitely gutting feeling after just putting it back together; go LS swap

 

Built motor without a way to monitor afr's?

 

Melted pistons. Could be poor tune, poor fuel, poor EMS with no safeties. You (or your EMS) must monitor AFRs and/or EGTs. If you're not willing to do that, run race gas or E85. That is a total loss, including anything in the oiling path (if separate oil for Vortech, then that should be fine) - sorry man.

 

It looks like preignition to me. A very poor tune.

 

Knock AND lean.

Going to put my bet on lean out/detonation. Clues: No AFR monitoring and "stock fuel rail."

 

Wonder if in addition to tune issues, there may have been assembly mistakes.

OP mentions scratches/scuffing on interior side of all six piston skirts.



"The presence of scuff marks on the lower skirt area would tend to indicate a lubrication problem rather than an overheating problem. Scuff marks on the edges or corners of the thrust sides of the piston would indicate bore distortion as the culprit. Scuffing on both thrust sides would indicate binding in the wrist pin.

Any time you find evidence of scuffing, therefore, it’s important to diagnose and correct the underlying cause to prevent a repeat failure.

If the engine was recently rebuilt, the scuffing problem may be due to insufficient assembly clearances. The only way to know is to measure the pistons and cylinders. Measure the pistons at the top, center and bottom of the skirt area in two directions (parallel to the wrist pin and perpendicular to the wrist pin) to see if the pistons are within the manufacturer’s specifications.

If the pistons are the correct size, then measure the cylinder bore at the top, middle and bottom, also in two directions (parallel to the crankshaft and perpendicular to the crankshaft). This will tell you how much taper is in the bores, and if bore distortion is a problem. By subtracting the piston dimensions from the bore dimensions, you can figure the piston-to-cylinder clearance. If the clearance is within specifications, the underlying problem is overheating."