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Old January 31st, 2017, 06:40 PM
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TJ's GMC TJ's GMC is offline
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Join Date: Mar 2015
Location: Cave Junction, Oregon
Truck: 1964 GMC 1500 LWB Wideside 305E V6.
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Default Re: Project Blown 305

The 305's are super common down there....so I'd grab a couple blocks and experiment on one with how far you can overbore. I'm speaking from what I have seen more than anything...when I had mine apart with the casting plugs pulled out of the block...it was nothing but huge water jackets between the bore spacing. Thereby somewhat confirming a Huge over bore would either cause premature cylinder failure or you'd hit water real fast. .060 over seems to be the common safe overbore size on most old engines. These things produced pretty decent torque as it is....so a bottom end lightening...more cam....lighter pistons....and some boost will wake them up big time anyhow. If I can't find a 478, eventually I'm planning on rebuilding the 305 somewhat like you are.
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1964 GMC 1500 305E/sm420 4 barrel intake mod and dual exhaust.
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