Marine RC engine fuel
08-09-2016, 09:23 AM
#1
Thread Starter
Marine RC engine fuel
What is considered to be a typical/acceptable fuel blend for the typical ringless tapered bore (ABC) marine engine? It seems most boat-specific fuels start at 30% nitro and go up from there, but there's rarely a mention of how much oil and what kind is typically used? I mix my own fuel and typically use castor and Klotz synthetic oils. It seems that marine engines typically use similar fuel mixtures that airplanes do with the nitro content being the only real difference. What are you folks using in your engines?
08-09-2016, 04:52 PM
#2
I use 18% lube, usually mixed castor/synth at 50% nitro.
Boats, in general, require more nitro than aircraft due to the higher RPM and greater load on the prop than an aircraft engine will be subjected to. Also, unless you're running a geared engine, the load will be applied to the engine's rear bearing and back plate, meaning more drag than on an aircraft engine as well. All that said, engines used in Europe are set up differently and run little to no nitro.
Boats, in general, require more nitro than aircraft due to the higher RPM and greater load on the prop than an aircraft engine will be subjected to. Also, unless you're running a geared engine, the load will be applied to the engine's rear bearing and back plate, meaning more drag than on an aircraft engine as well. All that said, engines used in Europe are set up differently and run little to no nitro.
08-09-2016, 06:21 PM
#3
Join Date: May 2007
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The smaller the engine, the higher the nitro is the general rule of thumb for maximum performance. The .12's & .21's love 60% & even 70% nitro! .45's & larger seem to do better on 50% or less. I've seen more than one high strung Nova Rossi or CMB that wouldn't really get on the pipe with less than 50%! Granted these are dedicated "race" engines......I've got stock K&B outboards that do just fine on 30%, but they fall into the sport category. What HJ said about oil is dead on 
08-09-2016, 07:04 PM
#5
Thread Starter
I'm reviving an old Graupner boat with an old OS .21 ABN engine (se-m model) which I've been told is basically a converted airplane engine... I test ran it on mild fuel - 10-15% nitro 20% oil at a 70/30 oil blend. It seemed to run fine - didn't have anything mixed with higher nitro except car fuel which I mix with just 11% oil/20% nitro. Maybe I'll mix up a quart of 30% to test out. I will see if the engine will hold up to some modern day abuse... If not, I'll get a good engine and stuff a tuned pipe into it. The boat is a POS though - not sure it'll handle a good engine.
08-10-2016, 11:14 AM
#6
Join Date: Jul 2005
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I'm running K&B outboards, 3.5 and 6.5. I use 15% Cool Power in both with good success and often use 30-35% heli fuel in the .21's. The one time I used a 65% nitro boat fuel it was low on oil. I found this out when I found two engines had broken rods. I'll stick to heli fuel and if I'm a little slower, well, ok.
Rick H.
Rick H.
08-10-2016, 02:52 PM
#8
If you want the engine to last, don't go lower than 18% oil, regardless of oil type. Car engines don't require as much oil since they don't have the side loading on the bearings and are normally run at 40K+ RPM.
08-10-2016, 03:40 PM
#9
Thread Starter
I agree completely. I run 10-11% oil in car fuel, everything else gets 20% oil minimum. By 15/20 and 20/20 I mean 15%nitro/20%oil and 20%nitro/20%oil. Lower oil fuel makes more power but at the expense of longevity generally.
