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.
>