I ran into a similiar situation a few years ago on a 400 that had less than 100 miles on it. Another shop had put the engine together. After tearing it down I took the crankshaft to the machinest I was using at the time, and upon pickup he told me that the crank had previously been turned .010-.010 and was .020-.020 when I picked it up. The mechanic that originally put the engine together put standard bearings on a .010 under crank. After I assembled the engine on startup it produced about 70psi cold and around 45 warm until it was broke in. Then it carried consistant 60psi cold at idle and 35 at idle when warm. Sounds like your builder may have done the same thing, if so get a builder that knows how to put an engine together properly and knows how to check clearances properly.
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1971 GTO,72 400, stock bottom end, 670 heads, Lunati BMII cam, headers, iron intake Q-jet, four speed. Best 60 ft 1.806in 2004. Best 1/8th mile e.t. 8.46 with 3.55 open rear
85 Grand Prix, 70 400, casting 62 heads stock rebuild, Turbo 350 trans 78 800 cfm Q-jet modified as per Cliff Ruggles book.
87 F350 6.9 4 speed dually
A poor man has poor ways.
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