What's a realistic rebuild scope for a used 6.0L before I can trust it?
It depends on its mileage and what you find, but these are the usual suspects on a high-mileage iron 6.0:
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- Piston rings: they commonly wear, causing compression loss and oil consumption. Replace them if compression is low or it burns oil.
- Pistons and overbore: worn cylinders may need boring back into spec, which means oversize pistons.
- Connecting rods: replace them only in extreme wear, or if you want stronger parts for power.
- Valvetrain: stronger valve springs and pushrods if you add a cam.
How much power the stock parts take: The stock LQ4 rotating assembly (cast pistons, powdered-metal rods, cast crank) is generally good for about 500–550 crank hp with a good tune. With boost or nitrous, many builders keep it around 450–500 rear-wheel hp for long-term reliability. The iron block itself is strong. Past that, plan forged pistons and rods.
A compression or leakdown test before you tear it down tells you whether you're looking at rings and bearings or a full machine-shop job.