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390 engine

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rodhhrod View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rodhhrod Quote  Post ReplyReply Direct Link To This Post Posted: Oct/18/2017 at 12:09pm
All numbers check good and it does say 390 on it. Too bad, pulled a head off yesterday and has 60 over pistons in it. So much for original, damn, not sure what I am going to do now.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpnjim Quote  Post ReplyReply Direct Link To This Post Posted: Oct/18/2017 at 1:44pm
+.060" is a lot for a 390/401,
but have the walls sonic tested before freaking out.

Factory spec says +.023 max,
rule of thumb says +.030" max,
but others have gotten away with more

+.060 = 4.225, but you don't know how thin the walls are until they're checked.

You could always list it for what you have in it,
hopefully the crank isn't +.030 already too 
^though even then the crabk can go .050+ on the mains, and the rods can go even more depending on what you're building.
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was Green/green now T/A red w/blk leather

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 70amxvegas Quote  Post ReplyReply Direct Link To This Post Posted: Oct/18/2017 at 3:26pm
60 over is ok .I bet there are a lot of them out there 60 over
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Oct/19/2017 at 7:01am
For a race engine 0.060" over might be okay, but thin cylinder walls mean higher temps, and a street 390/401 bored that much will likely have heating/cooling issues if driven any length of time. Not so important for drag cars -- can take time to cool between runs, and runs only last a few seconds.

jpnjim -- My best guess is the 401 as created because of competition more than anything else. Abernethey had set AMC up to compete head to head with the big three, and wanted to push AMC up into the mid priced segment (Buick/Olds/Pontiac/Mercury territory), and the competition all had 400 cubic inch engines. The upcoming changes in emissions/lower compression may have had something to do with it though, as cubic inches can make up for lower compression.
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rodhhrod View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rodhhrod Quote  Post ReplyReply Direct Link To This Post Posted: Oct/19/2017 at 5:55pm
The saga continues on the 390, Question- on the drivers side the piston notches are all facing forward on the upper left about 10 oclock. The passenger side the notch  are facing forward but on the lower right section about 5 o'clock. is this common or is there a screw up here. According to the TSM the notch should be upper forward. Sure could use some help here.
Rod
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