Lostpatrolman

iTrader: (3)

I have a stock bottom end and want to boost it. It appears that the first thing to go on these engines are the pistons. What would be involved with replacing just the pistons? WOuld the entire rotating assembly need to be rebalanced? Can the pistons and rods come out without removing the engine?

Camaro99SS

iTrader: (4)

You'll need to pull the motor and at least hone the cylinders for different pistons. And while it's out, new main, rod, and cam bearings would be a good idea. And yes the crank will need to be balanced for different (forged pistons). So you're looking at a rebuild.

Jason

Lostpatrolman

iTrader: (3)

Arent there any replacement pistons that are the same weight? How does GM get away with replacing one piston and leaving the rings alone when they warrenty the engine for piston slap?

Camaro99SS

iTrader: (4)

They spec the replacement pistons to be slightly larger to fit tighter in the bores. In essence, they used "custom fit" pistons. But the reason this fix doesn't work that well in all cars is because the cylinder walls are not honed again to allow the new rings to seat as well as they could. It's like taking a 100k mile engine that may still be running well and just putting in new pistons without any machine work to the block. The cross-hatch may still be visible, and the engine may have good compression but it's not condusive to the new rings seating as best as they could, resulting in oil consumption that was never really lowered or even lower cylinder pressure in many cases.

Now, could you still pull this off? Yes, but you would have to disassemble the engine and check the bores for any taper wear to guarantee anything. The cylinders would have to be as round as they were on day 1, and there would have to be enough cross-hatch present to guarantee a perfect seat, a must for best sealing, especially when boost is present.

The other area of concern is weight. Any other piston, forged or hypereutectic, will be of different weight then the OEM cast pistons. Balancing the rotating assembly for this change in piston weight is a must. There is no way around if you want the bottom end to live very long.

So in essence, either route you go, you will need to pull the engine and disassemble it. You might as well go the extra 1/4 mile and do it right.

Jason

GuitsBoy

iTrader: (4)

The key here is that the dealership will replace the single piston, however they will reuse the same rings.

Id say, just boost it till she blows, meanwhile start saving some coin for a built shortblock. Some stock shortblocks have held 800+ HP for a good while, yes others crap out at just over 500. Its a bit of a crap shoot and it will likely depend largely on how you treat the car.