390 high comp?
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From: Great Falls, MT
390 high comp?
I'm just learning bout motor internals and what not, so I don't really know about this kinda stuff. I was wondering if all 390's were high compression? (and what exactly high compression means? and how it's different from lower compressions) 
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From: The Vieux Ford, Kansas
Not all 390s were high compression really none of them it trucks there were a few that were but they were in cars. Compression is a ratio that measure the volume of a cylinder at bottom dead center versus top dead center so if you have 9:1 compression you take that volume and shove it into a space 1/9th the size at top dead center. When it comes to high compression its kind of a relative term, one motor that has aluminum heads and a good chamber design will run fine on pump gas at 11:1 but another with open chambered iron heads might have trouble at 9:1. There is no exact numerical line between high and low by typically over 9:1 would be call high and below it would be called low.
-Johnboy
-Johnboy
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Joined: Jul 2003
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From: iowa
Not all 390s were high compression really none of them it trucks there were a few that were but they were in cars. Compression is a ratio that measure the volume of a cylinder at bottom dead center versus top dead center so if you have 9:1 compression you take that volume and shove it into a space 1/9th the size at top dead center. When it comes to high compression its kind of a relative term, one motor that has aluminum heads and a good chamber design will run fine on pump gas at 11:1 but another with open chambered iron heads might have trouble at 9:1. There is no exact numerical line between high and low by typically over 9:1 would be call high and below it would be called low.
-Johnboy
-Johnboy
EX a 9.5 static cr motor with a stock cam, iron heads, may have around 8-8.6 dynamic cr and will ping under certain loads on 89 octane.
Ex number 2, we have a 10.0 alum headed motor with 248 degrees of duration at .050 lifterrise, and it will run on 89 octane. And it could be run with iron heads.
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