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Author Topic: 4.0 head swap compression ratio  (Read 3991 times)

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Alcoatari

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4.0 head swap compression ratio
« on: February 20, 2014, 05:59:38 PM »
Just a quick couple questions for the more advanced AMC gurus...

For the 258 + 4.0 head swap, I am curious what the product displacement and compression ratio will be.

I know I have come across this info before, but cant seem to find it. A link, a formula, anything will help.

I have the #7120 4.0 head.

My stock 258 is 8.3:1 CR.

These answers to these questions will supplement some supercharging calculations.

Trying to decide if the head swap could potentially hurt a supercharging application. If the 4.0 head raises the compression ratio substantially, this could decrease detonation limited power. I wont be going after super high boost, I have pretty stock equipment, so I want to keep boost between 5-8psi.

I plan on using an aftercooler as well as water injection, and would like to be able to use pump gas, so I want to keep effective compression ratio relatively low.

Thanks
« Last Edit: February 20, 2014, 06:05:14 PM by Alcoatari »
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Offline eaglefreek

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Re: 4.0 head swap compression ratio
« Reply #1 on: February 20, 2014, 07:34:41 PM »
What I have read is the combustion chambers on a 258 is 62cc and the 4.0l 57cc. 
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1986 AMC Eagle Wagon 4.2L/4.0L head, AW4,NP242, Chrysler 8.25" rear.
1981 AMC Eagle Wagon As Seen On TV  Lost In Transmission


 

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Alcoatari

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Re: 4.0 head swap compression ratio
« Reply #2 on: February 20, 2014, 08:47:45 PM »
Sweet, that helps. That means I can probably get away with a thicker head gasket
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Offline Draekon

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Re: 4.0 head swap compression ratio
« Reply #3 on: February 20, 2014, 10:03:03 PM »
This calculator claims that 58cc is the most common size combustion chamber for a 4.0l
http://www.jeepstrokers.com/calculator/
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Alcoatari

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Re: 4.0 head swap compression ratio
« Reply #4 on: February 21, 2014, 05:22:09 PM »
good link, thanks
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