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Date: Mon, 05 Sep 2005 12:51:40 -0500
From: Jim Sower <canarder@frontiernet.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Another great flying day = another day of troubleshooting
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If you're defining boost as over pressure, his SL pressure was 30" 
ambient + 36" boost 0 66" MAP and at 10k' he's got 26" ambient + 26" 
boost = 54" MAP
I think he's talking 36" MAP at SL and 26" MAP at 10k. 

Either way, MAP at altitude is a LOT less ... Jim S.


Ed Anderson wrote:

> Well, actually it is absolute pressure that the spark plug is reacting 
> to.  In this example, the absolute pressure in the intake is 1.234" HG 
> higher at 10,000 with your 26 " boost than at sea level with your 36" 
> of boost..  This would contribute to an increased pressure in the 
> combustion chamber when it is compressed over the sea level 
> compression pressure.  Therefore, the spark plug is facing a tougher 
> task at 10,000 than at Sea level (in this example).
>  
> Ed
>
>     ----- Original Message -----
>     *From:* David Leonard <mailto:wdleonard@gmail.com>
>     *To:* Rotary motors in aircraft <mailto:flyrotary@lancaironline.net>
>     *Sent:* Monday, September 05, 2005 12:57 PM
>     *Subject:* [FlyRotary] Re: Another great flying day = another day
>     of troubleshooting
>
>              Actually, Dave you had a higher pressure ratio (manifold
>             to ambient) at 10,000 feet with 26" boost than at sea
>             level with 36".  At sea level the pressure ratio would be
>             36/29.92 = 1.20.  At 10,000 ft ambient pressure = 20.57 "
>             hg , so the pressure ratio would  be 26/20.57 = 1.26.  Not
>             much greater, but it was higher by approx.1.23" Hg. (1.20
>             -1.26 = .06 *20.57 = 1.234" Hg).
>
>             Ed A
>
>     Right.  But what does the plug know about the ambient pressure?  I
>     thought that it was just the absolute density of the charge that
>     was contributing to SAG.
>
>     -- 
>     Dave Leonard
>     Turbo Rotary RV-6 N4VY
>     http://members.aol.com/_ht_a/rotaryroster/index.html
>     http://members.aol.com/_ht_a/vp4skydoc/index.html 
>