valve float rpm? - Dodge Cummins Diesel Forum
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post #1 of 6 (permalink) Old 07-23-2010, 10:49 AM Thread Starter
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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. ??


99 exlb 3500 auto 3.55 53 block unknown miles, stock other than bhaf and 4" exhaust
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post #2 of 6 (permalink) Old 07-23-2010, 11:04 AM
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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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post #3 of 6 (permalink) Old 07-23-2010, 11:06 AM
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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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post #4 of 6 (permalink) Old 07-23-2010, 11:18 AM Thread Starter
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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.

99 exlb 3500 auto 3.55 53 block unknown miles, stock other than bhaf and 4" exhaust
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post #5 of 6 (permalink) Old 07-23-2010, 12:09 PM
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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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post #6 of 6 (permalink) Old 07-23-2010, 02:02 PM
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On a correctly balanced and built engine the stock harmonic balancer and pushrods will be fine above 4k.

91.5 w250
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