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Carburetors, Mixers, Fuel Pumps and fuel delivery Discussion about misc. carbs, mixers, fuel pumps, injectors.

Carburetors, Mixers, Fuel Pumps and fuel delivery

Fuel Consumption Hit and Miss


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  #1  
Old 06-19-2018, 11:35:58 AM
David Cave David Cave is offline
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Default Fuel Consumption Hit and Miss

I recently heard a rule of thumb that fuel consumption for a hit and miss engine is : 1 gallon per hour per horsepower. Have you heard this rule or verified it. I will be running one of my engines loaded for several hours and was wondering. My first short run looked like 1/2 gallon per hour per horsepower.
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Old 06-19-2018, 12:12:03 PM
Andrew Mackey Andrew Mackey is offline
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Default Re: Fuel Consumption Hit and Miss

The fuel usage on a hit and miss engine, depends on the load. Just idling (no load), they are very fuel efficient. I had a 2 HP Stover KA that would run about 4 hours on a pint of gas, no load. A 5 HP Hercules would run about 8 hours on about a gallon and a half. Put a load on, and it's a different story. All in all though, I think your gallon/Hr per HP as you state it, is a bit high - even for a throttled engine of the time. For todays high speed engines, that might be a close number, but not the old stuff.
Hit and miss engines made their rated HP at the point where they hit at every compression stroke. That would be like a throttled engine running wide open. For both types, that indeed is a heavy load. Most H&M engines were under rated, due to the hit and miss nature. They actually made more power than the data plate read. The lighter the load, the more fuel you saved on a hit and miss. Fuel consumption was different too, due to the efficiency of the mixers the engine used. Earlier engines used more gas due to the fact that the fuel was 'mixed' with the air. As the manufacturers became better in their making of engines, they also made better means of vaporizing the fuel, which raised the HP and lowered the use of fuel.

What size and make is your engine? What are you driving with it? How constant is the load? it all ads up!
Andrew
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Old 06-19-2018, 12:17:05 PM
Kirk Taylor Kirk Taylor is offline
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Default Re: Fuel Consumption Hit and Miss

Quote:
Originally Posted by David Cave View Post
I recently heard a rule of thumb that fuel consumption for a hit and miss engine is : 1 gallon per hour per horsepower. Have you heard this rule or verified it. I will be running one of my engines loaded for several hours and was wondering. My first short run looked like 1/2 gallon per hour per horsepower.
I believe that rule is, "one pint per horsepower-hour." I also believe that an engine manufacturer used that figure in their advertising or operator's manual. Hopefully someone will reference it here.
If I did the numbers correctly, it works out to something like 17% efficiency.
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Old 06-19-2018, 12:31:53 PM
Andrew Mackey Andrew Mackey is offline
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Default Re: Fuel Consumption Hit and Miss

Under a load, you are probably pretty close, for a 11/2 to 3 HP engine.
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Old 06-19-2018, 06:17:48 PM
David Cave David Cave is offline
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Default Re: Fuel Consumption Hit and Miss

what little experience I have would indicate less than a half gallon so maybe a pint is correct.
I have a fairly accurate belt driven dyno that I'm thinking of using to test the idea. I'll run a 3hp engine on a 2 hp dyno load and a 1 1/2 hp engine at 1 hp load and see what happens. In September when it cools off.
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