So what is redline actually? I know my slant will run out of breath at 4500 but running out of breath isnt hitting redline, when should someone become concerned about grenading their motor?

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Drive it like its stolen, and be glad im not YOUR son...

Redline is the estimated maximum safe engine speed. The limit might be related to piston speed, valvetrain issues, bearings, bottom end strength, balance, harmonics, etc. Whatever the engineers thought was the weak link. A carefully built racing engine could have a much higher redline than a factory assembled grocery-getter mill.

Beyond the redline, you are pushing your luck. It might live. It might float the valves. It might throw a rod through the block.
Redline is not the same as the rpm at peak power or torque.

Doug Dutra says the slant six redline was set at 5500 rpm based on factory designs and equipment, in his article about oil pump gear failure.

http://www.slantsix.org/articles/oil-pu ... report.htm

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO