Date:         Thu, 13 Sep 2007 14:28:11 -0700
Reply-To:     "Mike \"Rocket J Squirrel\" Elliott" <camping.elliott@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "Mike \"Rocket J Squirrel\" Elliott" <camping.elliott@GMAIL.COM>
Subject:      Re: How do you check compression?
Comments: To: Mike S <mikes@FLATSURFACE.COM>
In-Reply-To:  <20070913210158.D567C1165C3@hamburg.alientech.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Like trying to blow up a balloon without being allowed to take a breath
first.

Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
KG6RCR

On 9/13/2007 1:59 PM Mike S wrote:

> At 04:26 PM 9/13/2007, Todd Last wrote...
>> Does it matter if the throttle is held wide open or left closed?
>> I recall some instructions which stated to have the throttle held open
>> when checking compression.
>
> Yes, it can make a big difference.
>
> Ultimate compression is something greater than the intake pressure X
> the compression ratio (greater because of adiabatic affects -
> compression makes the air hotter, which makes the pressure even greater
> than the CR would seem to indicate). If the throttle is closed, the
> intake pressure will be less than atmospheric (a partial vacuum), and
> therefore the indicated compression pressure will be less than you want
> to measure.
>