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Old 07-23-2010, 10:49 AM   #1 (permalink)
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valve float rpm?

what rpm does it take to float a valve? when i had the valve covers off they didnt say 60# on them so i would think they are stock. i thought it was around 3600, but the other day i wasnt watching the tach and i run 4k. after i snapped back of the peddle and said a few things, i pulled into the house and it still sounded and runs great. ??
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Old 07-23-2010, 11:04 AM   #2 (permalink)
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Snippet from cummins specs

Quote:
* Destructive torsional harmonic resonance occurs at 4100 RPM
* Crank and rods fail at 5400 RPM (if you make it through 4100 RPM)
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Old 07-23-2010, 11:06 AM   #3 (permalink)
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Oh yeah, valve "float" can happen at lower speeds in a force induction engine.

But you'd have to be running massive boost for that to happen.
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Old 07-23-2010, 11:18 AM   #4 (permalink)
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so if im understanding it wont happen untill 4100? im running 30psi, not massive but just enuff to clear the smoke.
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Old 07-23-2010, 12:09 PM   #5 (permalink)
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Yeah 30psi isn't going to push the valves open. The 4100rpm isn't valve float. It's harmonics in the engine. A fluiddamper, valve springs, and pushrods (on the exhaust side at least)are needed to safely run above 4K sustained.
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Old 07-23-2010, 02:02 PM   #6 (permalink)
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On a correctly balanced and built engine the stock harmonic balancer and pushrods will be fine above 4k.
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