Re: [Amc-list] LPG 258

[Jim Blair <carnuck@xxxxxxxxxxx>]

Static compression ratio is different from running ratio. Why do you think motors that breath better make more power? The "cork" was removed from the flow of air in the 4.2L when they went to the 4.0L head by raising the intake ports so there is a straighter shot at the valves by the air fuel mix. Why do you think people swap the 4.0l head on if the chambers were the same otherwise?

Jim Blair, Lynnwood, WA '87 Comanche, '83 Jeep J10, '84 Jeep J10
From: Matt Haas <mhaas@xxxxxxx>
Subject: Re: [Amc-list] LPG 258
To: "AMC/Rambler owners, drivers and fans." <amc-list@xxxxxxxxxxxx>
Message-ID: <48E950B2.2010202@xxxxxxx>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
 
Since when did VE have anything to do with compression ratio? If the 4.0 
head has a smaller combustion chamber, than compression goes up but how 
well the head flows doesn't magically change the physical properties of 
the motor.
 
Matt
 
On 10/5/2008 1:59 AM, Jim Blair spouted this sage advice:
> Actually, since the VE (volumetric efficiency) goes up with the 4.0L head (even more with the HO head) the compression will go up slightly.
> 
> Jim Blair, Lynnwood, WA '87 Comanche, '83 Jeep J10, '84 Jeep J10
> 
> From: Frank Swygert 
> Subject: Re: [Amc-list] LPG 258
> To: amc-list@xxxxxxxxxxxx
> Message-ID: 
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> Look for different pistons -- you can only go up maybe one full point by shaving the head alone. Compression doesn't go up with the 4.0L head on a 258 -- only 8.7:1 (stock 4.0L). The combustion chamber sizes are the same on the 258 and 4.0L.
> 
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