Hello everyone,

Well to start, this was my first 4G63 build. Mods are fp black,stock block/crank. manley rods and wiseco pistons. ported head, 272 cams, dual valve springs, 355 fuel pump, 1050cc injectors, fp intake, main studs and l19 head studs.

I had the car running all summer driving at around 20 PSI on a base tune. Due to delays on getting my car at the dyno. I put about 900 miles on the car with no problems.

We started on the dyno with about 3 pulls to dial in the fuel. On the 4th pull the fueling was great and then the engine just stopped.

We started cranking it and it spun over like the timing jumped or the valves were not moving.

After pulling the timing cover and seeing that the belt didnt jump, we pulled the valve cover. All the valves were moving so we checked compression.

cylinders:

1= 0 psi
2= 30 psi
3= 0 psi
4= 0 psi


So I towed it home and pulled the head. The tops of the pistons were blown apart around the ring lands. Usually a sign of pre-detonation. With the fueling in the tune it wasn't too lean and the timing was dialed down since we weren't doing power pulls.

So back to the drawing board to figure out what caused this. After checking to the shop we dyno'd the car and by engine blue prints, we found that the piston to wall clearance was too tight.

The piston expanded and touched the wall creating heat and causing hot spots on the piston in turn causing the pre-detonation.

When I had the engine bored, the machine shop wanted the pistons so they could bore it per the pistons specs. However, in the turbo/nitrous application on the Wiseco charts, this spec is too tight for making higher boost levels. The piston expands more than the tolerances given.The tolerance is around .0025 and everyone at the shop I had it dyno'd at said it should be around .0045 of wall clearance.

When doing the build, I didn't think to check online to see what shops or other builders bore their engines too for piston to wall clearance.

Has anyone had this problem? Also, should Wiseco change their specs for the racing applications for their forged pistons?

 

I have noticed wiseco's give their pistons a very low P2w, I suppose they are made out of a different alloy aluminum than most others...and I have had a few people do it via their spec, with poor results. I usually have my motors machined a little on the looser end.

 

Thanks for the input. What wall clearances do you use and what pistons?

 

.0025" is far too tight. depending on the exact application, most are set to .004"-.005".

 

you also need to realize that Wiseco has a teflon coating on the piston that they are taking into account when recommending the PTW clearances. Once that is qorn off the clearance would be closer to what others are saying it should be.

 

Where are the pics i want to see this awesome.

 

Was your tuner using det-cans while tuning so he could hear detonation?

 

Where did you have the car tuned?

 

Where did the machine shop measure the piston width? at the dome or on the skirt?

 

The car probably wasn't detonating. P2w clearance that tight is suicide with forged pistons. Wiseco's specs are tighter than most, and they recommend .0035-.0045 clearance

 

who speced out this piston clearancing? Whomever did, owes you the rebuild...

 

Why are the tops of the pistons destroyed if the piston to bore clearance is too tight?
Broken ring lands is usually from detonation.

P2W clearance too tight will result in massively damaged bores and/or a gudgeon pin pulled out of your pistons.

So what was the final P2W clearances?
0.0045?

 

broken ring lands often happen from too tight of ring end gap.