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460 compression ratio for 87 octane?

 
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Old 12-22-2009, 09:02 PM
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460 compression ratio for 87 octane?

i'm rebuIlding the 460 in my 84 ford, I got the cobra jet timing set to advance the cam, hedman log tube headders, and edelbrock performer intake, and a decent rv cam. im just trying to figure out what CR i should go with. i dont want to run premium fuel because it drinks it way to fast! So what would be a good number to shoot for? any help would be great!! thanks
justin
 
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Old 12-22-2009, 10:12 PM
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With everything you named off it wont change your compression ratio at all. If you were to upgrade your cylinder heads and maybe they had a different size combustion chamber then it would go up and the same thing when changing piston head type's. You can google compression ratio calculator and it will give you directions on what different things will change compression ratios. The thickness of a head gasket will also help pin pointing a exact ratio But to answer your question you wouldnt want to go above 7 or 8 if you want to stick with 87 octane.
 
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Old 12-23-2009, 01:35 AM
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Im sorry, i guess i should of said i was trying to figure out the CR because im getting ready to order the pistons. my bad....
 
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Old 12-23-2009, 09:58 AM
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I'd shoot for 8.0-1 to 8.4-1 or so. I've read that you can run higher compression if you get the quench good and tight by decking the block or running a taller piston with more dish instead of using a shallow dish set deeper in the bore.
 
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Old 12-23-2009, 01:12 PM
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In reality an 8.4 to 1 is way low for using 87 octane for optimum power. A 9.0 to 1 is closer to what you want and will up the power output some over stock. Do not go over 9.5 to 1 if you want to continue to use 87 octane.
 
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Old 12-23-2009, 02:38 PM
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Originally Posted by Bear 45/70 View Post
In reality an 8.4 to 1 is way low for using 87 octane for optimum power. A 9.0 to 1 is closer to what you want and will up the power output some over stock. Do not go over 9.5 to 1 if you want to continue to use 87 octane.
That may be pushing for detonation with 87 octane, whats the stock Compression ratio? I wonder what the owners maual says for type of gas to use. Anyway yeah decking the block will also up the compression a bit.
 
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Old 04-05-2013, 05:08 PM
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Originally Posted by Bear 45/70 View Post
In reality an 8.4 to 1 is way low for using 87 octane for optimum power. A 9.0 to 1 is closer to what you want and will up the power output some over stock. Do not go over 9.5 to 1 if you want to continue to use 87 octane.
I would tend to agree with this. If you are running 8.0 to 8.5, there had better be a forced induction system to go on top of it. The duration of the cam has a lot to due with the recommended compression, usually the longer the duration, the higher the compression that is recommended by the cam manufacturer. The higher compression requires higher octane, but that is only really a problem when you are on the throttle. Your timing is usually the culprit for "pinging".
I haven't done the research, but I have heard people state that aluminum heads are not as prone to pre-ignition as cast iron.

I am about ready to build another 460, I'm shooting for around 9.5, I've heard of people getting away with much higher than that.
 
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Old 04-06-2013, 10:32 AM
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It isn't much more per gallon for 89. When you add it up, say it's .06 more per gallon thats still less than one dollar per 15 gallons. Looks very affordable when you do the math. That 87 stuff is JUNK.
 
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Old 04-06-2013, 11:33 AM
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My rebuilt 460 has 9.5:1 compression and I have no problem running 89 octane. I know its not 87 octane, but like Mark said, it really isn't that much of a price difference. Not sure where you are from, but here in Missouri at Casey's General store (where I buy gas), the price is the same.
 
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Old 04-08-2013, 07:25 AM
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Originally Posted by mark a. View Post
It isn't much more per gallon for 89. When you add it up, say it's .06 more per gallon thats still less than one dollar per 15 gallons. Looks very affordable when you do the math. That 87 stuff is JUNK.
In some areas (here in Iowa), 89 octane is E10 blend. 87 got 1-2 mpg better than 89 E10, but 87 is also usually $0.10/gallon higher priced than 89.
 
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Old 04-14-2013, 08:25 AM
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Where are you at? what elevation? What are you doing with it? If you are higher in elevation you need more compression. I run 85 pump gas in iron headed 10:1 and higher engines with NO problems. I am at 6000 ft in elevation too.

If you are going to tow much though, don't shoot much over 9.0:1 due to the heat and all.

Run a cool thermostat helps as well, I run a 160 and I went to a 195 for this last winter and definetely hurt my 10:1 460 on 85 octane. It was not as happy.
 
 
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