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Matt Dralle
Site Admin
Joined: 08 Nov 2005
Posts: 26321
Location: Livermore CA USA
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 Posted: Thu Mar 31, 2011 9:01 am Post subject: Low RPM/High MP vs. High RPM/Low MP... |
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Dear Listers,
With the IO-390 and Hartzell 72" CS on my RV-8, a combination of 2150 RPM and 25-26 MP gives me nice 200MPH True and about 10.5-10.8 GPH. These number are down low, maybe 3000ft. Higher altitude gives lower GPHs. At 2150, the cockpit is pretty quiet too.
Increasing the RPM and Decreasing the MP doesn't really change the GPH that much, but starts dropping the speed.
In all configurations, I'm running LOP at about 1360 on the hottest cylinder. Oil temps are about 178 F. Max MP at low altitude is about 28-29.
Are there any issues running in a low-RPM, high-MP configuration as described above?
Thanks,
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Matt Dralle
RV-8 #82880 N998RV
http://www.mattsrv8.com - Matt's RV-8 Construction Log
http://www.youtube.com/MattsRV8 - Matt's RV-8 HDTV YouTube Channel
Status: 160+ Hours TTSN - Paint job is all that's left...
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Matt Dralle
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Matt Dralle
Site Admin
Joined: 08 Nov 2005
Posts: 26321
Location: Livermore CA USA
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| Posted: Thu Mar 31, 2011 7:59 pm Post subject: Low RPM/High MP vs. High RPM/Low MP... |
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Hum, interesting. In that graph, albeit for the IO-360, the "Limiting MP For Continuous Ops" at 26 MP is 2100 RPM. 27 MP is 2200. Assuming the IO-390 is similar, 2150 at 26.5 ought to be good to go. BTW, I flew tonight and at 26/2150 I was seeing about 10.2-10.5 GPH (at) 2500ft. Better than I recalled.
Where can I get a sweet chart like that for my IO-390? I looked quickly though the manuals that came with the engine, and I didn't see one.
Thanks for the feedback everyone!
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Matt Dralle
RV-8 #82880 N998RV
http://www.mattsrv8.com - Matt's RV-8 Construction Log
http://www.youtube.com/MattsRV8 - Matt's RV-8 HDTV YouTube Channel
Status: 160+ Hours TTSN - Paint job is all that's left...
At 10:07 AM 3/31/2011 Thursday, you wrote:
[quote]Matt,
I don't have an IO390 but the manual for my IO360B shows that combination as outside of the suggested area of continuous operation - yes it was a quick look and I didn't purely run the numbers.
I would guess that combination might be detonation-prone.
YMMV - see if you can get the appropriate chart for the IO390. They are a bugger to figure out too - but there are some guidelines.
Ralph
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gcomfo(at)tc3net.com
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| Posted: Fri Apr 01, 2011 3:40 am Post subject: Low RPM/High MP vs. High RPM/Low MP... |
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gcomfo(at)tc3net.com
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| Posted: Fri Apr 01, 2011 4:39 am Post subject: Low RPM/High MP vs. High RPM/Low MP... |
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