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70 390 compression with FelPro head gaskets |
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imacarfan2 
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Joined: Jul/01/2007 Location: Northeastern MA Status: Offline Points: 971 |
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 Topic: 70 390 compression with FelPro head gasketsPosted: Apr/08/2021 at 9:57pm |
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I'm redoing the gaskets on my 70 390 as it's leaking like a stuck pig. Being a 70 with 291 heads, the stock compression is around 10:1. Anyone know how much the compression will change with FelPro head gaskets? Will they lower the compression much at all?
I know I didn't HAVE to pull the heads when redoing the gaskets, but I wanted to see what the cylinders looked like.
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67 Ambo conv
68 AMX 68 Ambo 4 door 70 Ambo 4 door (2) 71 Hornets (1 SC/360) 73 Hornet 2 door 77 Matador coupe 77 Sportabout 78 Concord 2 door 81 Concord wagon |
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PHAT69AMX
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Posted: Apr/08/2021 at 11:55pm |
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How thick are the gaskets taken off? What diameter is the gasket piston hole?
How thick are the new FelPro Gaskets you're gonna put on? What diameter is the gasket piston hole?
Edited by PHAT69AMX - Apr/08/2021 at 11:57pm |
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imacarfan2
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Posted: Apr/09/2021 at 8:03am |
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The gaskets that were on there were factory AMC gaskets (has the AM mark on it!) and stock bore. The FelPros are the standard 343, 360, 390, 401 head gaskets with a 4.27 hole and I believe .045(?) compressed.
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67 Ambo conv
68 AMX 68 Ambo 4 door 70 Ambo 4 door (2) 71 Hornets (1 SC/360) 73 Hornet 2 door 77 Matador coupe 77 Sportabout 78 Concord 2 door 81 Concord wagon |
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6PakBee
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Posted: Apr/09/2021 at 8:25am |
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Assuming you are going from a 0.020 gasket to a 0.045 gasket that's a little over 1/2 a point in CR by my calculations.
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Roger Gazur
1969 'B' Scheme SC/Rambler 1970 RWB 4-spd Machine 1970 Sonic Silver auto AMX All project cars. Forum Cockroach |
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imacarfan2
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Posted: Apr/09/2021 at 10:45am |
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Is the factory gasket only .020?
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67 Ambo conv
68 AMX 68 Ambo 4 door 70 Ambo 4 door (2) 71 Hornets (1 SC/360) 73 Hornet 2 door 77 Matador coupe 77 Sportabout 78 Concord 2 door 81 Concord wagon |
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SC397
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Posted: Apr/09/2021 at 11:33am |
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Fel-Pro gaskets compress to .043"
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6PakBee
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Posted: Apr/09/2021 at 12:42pm |
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Roger Gazur
1969 'B' Scheme SC/Rambler 1970 RWB 4-spd Machine 1970 Sonic Silver auto AMX All project cars. Forum Cockroach |
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PHAT69AMX
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Posted: Apr/09/2021 at 3:55pm |
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And there was an AMC Service Bulletin later on that changed out the original head gasket for a thicker one and it included installing longer Push Rods also to go along with the thicker head gasket.
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imacarfan2
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Posted: Apr/09/2021 at 9:23pm |
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I checked the used factory gasket today and came up with around .036 (.0355-.0365).
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67 Ambo conv
68 AMX 68 Ambo 4 door 70 Ambo 4 door (2) 71 Hornets (1 SC/360) 73 Hornet 2 door 77 Matador coupe 77 Sportabout 78 Concord 2 door 81 Concord wagon |
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Heavy 488
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Posted: Apr/09/2021 at 9:49pm |
And that's already been compressed so most likely a negligent difference
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imacarfan2 wrote: