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390 engine |
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rodhhrod
AMC Addicted Joined: Jul/11/2010 Location: Oregon Status: Offline Points: 1040 |
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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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jpnjim
AMC Addicted Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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+.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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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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70amxvegas
AMC Addicted Joined: Apr/26/2009 Location: Lost Wages Status: Offline Points: 1791 |
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60 over is ok .I bet there are a lot of them out there 60 over
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farna
Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19611 |
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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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Frank Swygert
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rodhhrod
AMC Addicted Joined: Jul/11/2010 Location: Oregon Status: Offline Points: 1040 |
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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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