What exactly is piston slap and what does it sound like. My built motor make a funny noise and i was told it might be piston slap. Its not a knock because it has been doing this forever and my oil pressure has remained the same at 80-85psi cold.

 

Piston slap is when the pistons slap the cylinder walls when they travel up and down. Forged pistons do this since they run larger clearances. Cast(stock) pistons are tighter clearances, therefore there is no slap.

The piston slap should go away after the car is warmed up since forged pistons expand under heat.

It sounds like a diesel truck, almost exactly like a disel.

 

It would sound like you have a squirel loose in your engine. But seriously, piston slap is the sound of the pistons banging around in an abnormal motion. Some aftermarket forged pistons require a larger piston to wall clearance to allow for growth once they warm up. (metal expands as it heats) Some pistons dont require as much... My Endyn pistons are quiet as stock for example.

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<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">It sounds like a diesel truck, almost exactly like a disel.</TD></TR></TABLE>

This is exactly what I was thinking...

 

That must be what it is then. Mine are SRP forged pistons and when its been sitting over night and it gets down below 45 degrees or so I can hears it much more then its in the 80s or 90s. Once the car warms up i still hear it but not as much as when its cool.

 

also described as the sewing machine effect...

 

When start up cold, it does sound like a diesel truck and goes away after it's at normal operating temperature.

 

when I was breakin in my endyn's, they were loud as ***! My car sounded like a bus, especially when cold...but now they are actually quieter than stock. sometimes when I'm sitting in traffic, I could barely hear the engine, and I would think that the engine stalled.