Quote:
Originally Posted by glc
I have NEVER hit the RPM limiter - just the speed limiter. The engine is making a LOT of racket before it hits the limiter, and the acceleration is dropping way off, so I don't see the need to try to hit it! I think the highest I've ever had it is about 5200.
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x2. By 5,000 rpm, my motor is making only noise, not power. No reason not to shift by then. I think I took it up to 5200 rpm one time, when I first got the Superchip. Even then, it would accelerate quicker shifting much earlier.
I can't imagine intentionally taking it to 5,400 (the reported stock rev limiter).
I can imagine floating a 4.2 valve before 5400 rpm, especially on a high mileage motor that may have a tired valve spring.
FWIW, I've floated valves many times (never on a 4.2) but was lucky to get off with bent pushrods, or no damage at all. Once the valve gets out of control, the luck of the draw says occasionally it's going to be hanging out there long enough to kiss a piston.
For all we know, the OP's 17 year old son who is used to driving a high revving import borrowed his truck the day before the valve touched the piston.
Basically, short of some sort of random part failure, I'm having a hard time coming up with a scenario where rpm is not a factor when a valve touches a piston.