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Run times with Various Heads
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Run times with Various Heads
Just was curious. Does anyone know.
I know that the head inserts with OS Number 8 runs slower than cox high compression head by about 3-4 K RPM. I know the Merlin 2019 head runs almost the same as the original Cox head.
I'm in quarantine right now as a precaution so can't get out for actual comparison test hence the question to you.
The head adaptor that is slower by 3-4 K does it use less fuel? I mean does it pick up run time due to the lower RPM? I never tested that before. Normal runs for 17K are like 2.5- 2.75 minutes per tank. Might the slower head run time achieve an additional 60+- seconds of "slower" run or at least proportionally to its comparable high compression head run?
Anyone have any stats or experience to share?
Thanks
Iceberg
I know that the head inserts with OS Number 8 runs slower than cox high compression head by about 3-4 K RPM. I know the Merlin 2019 head runs almost the same as the original Cox head.
I'm in quarantine right now as a precaution so can't get out for actual comparison test hence the question to you.
The head adaptor that is slower by 3-4 K does it use less fuel? I mean does it pick up run time due to the lower RPM? I never tested that before. Normal runs for 17K are like 2.5- 2.75 minutes per tank. Might the slower head run time achieve an additional 60+- seconds of "slower" run or at least proportionally to its comparable high compression head run?
Anyone have any stats or experience to share?
Thanks
Iceberg
Iceberg- Gold Member
- Posts : 381
Join date : 2018-11-03
Location : Suva Fiji Islands
Re: Run times with Various Heads
It make sense To me as the engine wil breath faster and stronger tink it can afect the flight time
davidll1984- Diamond Member
- Posts : 2293
Join date : 2020-02-12
Age : 39
Location : shawinigan
Re: Run times with Various Heads
Common knowledge is that a tighter combustion chamber gives the best mileage. Smaller place for the fuel to fit. More efficient as well. In practise, a smaller prop is used, so it revs more which wastes fuel. I would think that a huge load prop with a TD head would give the best run time---if it will run reliably. Sometimes they will just flop back and forth. I have not tested it though. Just my thoughts.
aspeed- Platinum Member
- Posts : 790
Join date : 2013-01-18
Location : Leamington Ont. Can.
Re: Run times with Various Heads
I absolutely concur aspeed. I've had engines that would do the back and forth flop due to over compression. I'd use an electric starter on them, and the they run like a scalded something(my cat's in my lap). Same goes for under compressed engines(clapped out).aspeed wrote:Common knowledge is that a tighter combustion chamber gives the best mileage. Smaller place for the fuel to fit. More efficient as well. In practise, a smaller prop is used, so it revs more which wastes fuel. I would think that a huge load prop with a TD head would give the best run time---if it will run reliably. Sometimes they will just flop back and forth. I have not tested it though. Just my thoughts.
Granted, I wouldn't make a habit of starting with an electric starter, without the usual prop plate/case shim in place.
Bob
dckrsn- Diamond Member
- Posts : 2750
Join date : 2010-10-21
Age : 71
Location : Long Island, New York
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