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1968 390 pistons work in a 1970 390 |
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AMXFSTBK390 
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Joined: Oct/22/2013 Location: SF Bay Area Status: Offline Points: 3489 |
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 Topic: 1968 390 pistons work in a 1970 390Posted: Sep/16/2018 at 3:01pm |
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I disassembled my 1968 AMX original 390 engine that was rebuilt by previous owner. Oddly, it has 1970 401 rods # 3197047 with .040 pistons. Are the pistons custom ordered with a relocated wrist pin to fit the 1968 390 block? The reason I ask is will these pistons work on 1970 connecting rods in a 1970 390 block? The reason I ask is a member here would like to install these pistons in his 1970 390 block that is already bored to .040 All comment greatly appreciated.
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AMXFSTBK390
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Joined: Oct/22/2013 Location: SF Bay Area Status: Offline Points: 3489 |
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Posted: Sep/16/2018 at 3:21pm |
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PS: Second attempt to post picture of the 390 .040 pistons with 401 connecting rods in my original 1968 390 AMX block.
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401MATCOUPE
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Joined: May/20/2010 Location: Salisbury, MD Status: Offline Points: 5367 |
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Posted: Sep/16/2018 at 7:34pm |
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the 3197047 rod is 70 390 and 71-up 401 both.....are you sure the block you have is 68/69 not a 70? What size are trhe head bolts? What is the casting number at the back of the drivers side block?
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Ross K. Peterson
68X,GoPac,343,AT,52A(1stCar) 68X,GoPac,390,4sp,52A 69X,GoPac,390,4sp,64A 70X,GoPac,390,4sp,87A,8 70X,GoPac,390,4sp,BBO,8 70 Jav SST,390,AT,BSO 74MatX,401,AT,Prototype 74MatX,401,AT |
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Ken_Parkman
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Posted: Sep/16/2018 at 8:24pm |
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A 401 rod is .068" longer, and an early 390 is supposed to have .045" deck. depending it might actually work, especially if the pistons, being replacement, are a touch shorter or the rods were resized. But the compression is probably way higher than you thought.
The 70 390 got the zero deck, and a different piston with a larger dish. Early pistons in a 70 390 results in a very high compression. You will have to measure it all to figure it out.
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AMXFSTBK390
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Posted: Sep/16/2018 at 9:46pm |
The block casting # is 3190806 which 68-69 AMX 390. The rectangular port heads to block uses 7/16" bolts. My recent thinking is because of the different rod lengths and compression heights between the 1968 and 1970 390's all eight matching pistons must be used, but the compression ratio will be something different than the norm, and so too the quench aspect?
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401MATCOUPE wrote: