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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
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