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Old 01-30-2019, 07:24 AM
Hydro Junkie
Join Date: Nov 2004
Location: Marysville, WA
Posts: 7,772
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Originally Posted by ramboy View Post
How is a gas engine less labor intensive vs. a glow engine?
Appowner kind of covered it in his last post, so I don't need to rehash all of that.
When I compare operating costs of my CMB 67 nitro motors to my CMB 27 gasser, the difference is considerable:
1) 50% nitro fuel costs roughly $35 per gallon, 100 octane gas costs around $5 per gallon, not counting the required 2-stroke oil
2) Glow plugs last, normally at best, three or four runs and cost around $5 each, spark plugs routinely last a whole season and cost less than $10 each
3) My CMB 67s will burn through 16-20 ounces of nitro fuel in a 5 minute heat, the CMB 27 will burn through 10-15 ounces of gas/oil in a 5 minute heat
You have to remember, I'm comparing marine racing engines which run roughly twice as fast as a comparable airplane engine and burn over twice as much fuel doing so. When I compare the specifications on my CMB 67 to an OS 65LA, here's what I get:
OS 65 LA lists out at .662 ci, 2000-16000 rpm, 1.7hp/16000 rpm. It has a bore and stroke of .954 inches and will swing 12X7/8 and 13X6/7/8 sized props
2004 version of the CMB 67 lists out at .669 ci, 2500-28000 rpm, 4.7hp/27500 rpm. It has a bore of .968 inches and a stroke of .909 inches. The larger bore and shorter stroke, IIRC, give the marine engine more torque than the OS aircraft engine even though it's operating in a much higher powerband. My present boat runs a Prather 255 stainless steel 2.4X3.8 prop that is balanced, polished and sharpened

Last edited by Hydro Junkie; 01-30-2019 at 07:32 AM.
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