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Post by Andy Wood on Sept 5, 2009 16:30:44 GMT -5
I've been looking into the RPM limits of both Cast and steel cranks I was wondering what other people think about this subject.
my point of view is HP and TQ have the final say and if the rotating assembly is light enough and if its balanced right you should be able to to run the cast crank just as high as the forged unit.
I build mostly 4.6 Fords and I know for a fact a stock cast 4.6 crank will live at 700 hp and 7000 rpm..
Andy
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gman
Building Boost
Posts: 163
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Post by gman on Sept 13, 2009 8:59:28 GMT -5
Andy,
It is more about what you are doing at the top end of the connecting rod (i.e. : compression ratio, boosted, or NOS), and less about RPM's
The violence of what you are trying to squeeze, and unusual harmonics, that is what will crack cranks, even steel cranks.
I agree that a good balanced cast assy will live at a higher RPM than a non balanced one. As long as you have a good balancer and have your crank checked for cracking periodically (every season), then you should be good.
Not sure what kind of timing drive that a 4.6 has, if it has a chain you are better off, than if it has a gear drive, chain doesn't transfer the harmonics like a gear drive.
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Post by krobinson on Sept 13, 2009 9:14:22 GMT -5
Big killer of cast cranks are two steps. They really get the best of cast cranks. I believe that was the ending of my old 331.
Zero balance sure helps and no detonation.
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Post by BACKNBLACK on Sept 18, 2009 22:29:06 GMT -5
I HAVE ALWAYS BEEN TOLD THAT CAST CRANKS ARE FINE UP TO 7000 RPMS, THEY ARE LIGHTER THAN STEEL SO SHOULD REV QUICKER, ALWAYS BALANCE THE ASEMBLY, FREE HORSEPOWER AND LIVE LONGER, BUT HAVE ALSO BEEN TOLD CAST CRANKS DO NOT CRACK THEY JUST BREAK? HAS ANY ONE ELSE HERED THAT STORY??
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