caddydaddy472

I have a K&B 7.5 in my boat, and the local hobby shop doesn't sell boat fuel, but recommended Byron Gen2 car fuel. It's 30% Nitro with 11% oil. I'm pretty sure boat motors need more oil than that because of the high loads, but he said it's all the same!???
I'd think I could just add oil to this gallon jug to bring the oil percentage up. What would I use and how much?

Thanks!

JCINTEXAS

Hi Steve,
Years ago I used to blend model engine fuels for model planes and boats. The brand was Dynaknight Fuel. You're right about boat engines having higher loads on the conrod and wrist pin simply because water has a much higher density than air. And boat props typically go to very high rpms when they lift out of the water and then get a very high load when the prop drops back into the water while running at high speed. I would suggest you don't need any more than 15 percent total oil content by volume. You can't go wrong by adding 3 or 4 percent degummed (Baker's AA) Castor Oil. Easiest way to do this would be to measure 96 ounces of your 11% car fuel and then add 4 ounces of Castor oil or Klotz. You will probably need to adjust your needle valve a little richer as your fuel will have a little high viscosity after you add the oil.
JC

1QwkSport2.5r

Boat engines should run 18-20% total oil generally. If the engine only spent 2-3 seconds at WOT you could get away with 12-14% oil. Look at the oil content of most boat fuel and compare it to car fuel.

caddydaddy472

Iagree! Ireally didn't believe what the guy at the hobby shop was telling me that all fuels are the same. I'll just add some oil to this fuel.

Thanks!

1QwkSport2.5r

To add enough oil to get the total content up to at least 18% is going to drop your nitro content by 5-10% roughly. If you haven't opened it, I'd return it and buy the right fuel. 12oz extra oil gets you to roughly 18.5% oil, but over a gallon (140oz) total quantity. Nitro will be somewhere around 25% roughly.

caddydaddy472

Thank you.  I might just use it in my airboat instead.
  I guess I'll just have to mail order fuel for my boat.  This place never seems to have the fuel I want!

1QwkSport2.5r

You can't use car fuel in aircraft engines either. Aircraft and boat engines need 18-20% oil. Car engines are usually the only glow engines running that low of oil content besides the 30cc and up Super Tigre engines.

I run 5% nitro 20% oil in my aircraft engines, and 20% nitro 12% oil in my cars.

caddydaddy472

Roger that. I'll return this fuel.  

GallopingGhostler

One can bring up the oil content to acceptable by adding Klotz Benol Racing Castor Oil to it. Of course it would reduce the amount of nitro. But you are correct, usually it is cheaper just to buy the right fuel, unless the shop will not accept fuel returns. Problem is nearly all modern fuels lack adequate oil for especially the older steel cylindered with soft steel or iron piston engines, and even for some of the ABC's.

I'm finding that even some ruined the AAC K&B Sportster engines by running too lean or with inadequate oil. I had a recent E-Bay buy where the seller claimed excellent compression. It came with zero compression. After disassembling, I found that the squishband (upper) portion of the chrome plated aluminum piston was missing its chrome plating. Fortunately, a CL friend sent me two parts engines. From the three I now have one good one.

1QwkSport2.5r

I never said it can't be done, but to get 11% oil fuel to 18% would require 12+ ounces of oil and require two jugs to mix it all up. Not exactly ideal circumstances if you ask me. Not knocking it at all, just being realistic IMO.

Benol doesn't mix worth crap with some glow fuels, Byron's and Odonnells being two. SIG's castor is fine, and klotz techniplate is fine too.

I won't buy a used Sportster for the very reasons you stated. I just don't believe for one second that a fuel with any synthetic at all is going to run a sportster the way it should. Like many other engines, they were designed around castor oil in the fuel and not a synthetic. Look at be OS peeling liners... Most of the stories I've read, those users were using fuel with little or no castor. The guys that aren't afraid of castor don't get peeled liners as often. Granted, its probably coincidence.... OS is top quality and should be put on a pedestal. Okay maybe not a pedestal...

It is my opinion that special circumstance engines need a special diet. Bushed, lapped, and weird cylinder construction engines like the sportster should get a full castor diet, I prefer 25% oil for those engines.

This is all just my inflated humble opinion. I mean no offense, and I come from the "old school" belief that castor is king. To goo or not to goo is the question. I'll take the goo.

GallopingGhostler

What you state has a conservative approach but not without reason, 1QwkSport2.5r. I grew up in the all Castor fuel era and it used to be before that one did not have to worry about the fuel that they used, whether it was safe or not for the engine. One just bought and enjoyed.

I am told that the Sportster (in this case mine is a .20) is a very good engine for CL use. It is frugal on fuel and spins a 10x5 prop all day. I am told it has about the power of an OS .25 FP or LA. Of course the CL fliers use 24% oil content in a rich wet setting with a mild amount of nitro for smooth running. Under those conditions the engine lasts a long time.

Interesting that Benol doesn't mix well with O'Donnells fuel, since Tower Hobbies (Hobbico) bought O'Donnells and Klotz Benol is the Castor oil they sell.

1QwkSport2.5r

Benol is a modified castor. I believe the term is polymerized. It is designed to mix well with gasoline, though it is supposed to mix with methanol still. I saw some pictures in the R/C car forum earlier this year of some Byron's gen2 car fuel with blue or green (couldn't tell the color from the photo) oil on the bottom of the container. I'll see if I can find it. I have not used Benol myself, it's $12/qt at my hobby shop. Besides, I have 2 gallons of regular SIG castor.

I have Sportster .65's, a pair from the military RCMAT program. I put civilian carbs on them and they run better than ever. They don't like more than 5% nitro and run better/turn faster rpm on 25% oil than 20%. Mine are good on fuel and will turn some serious prop load. I love their sound too.

Nonetheless, I'll try to find the picture of the non-miscible Benol and post it here. It's quite odd.

1QwkSport2.5r

I'm working on finding the picture I referenced to in the last post... I have to amend my previous post - the fuel that wouldn't mix was Odonnells, not Byrons.

GallopingGhostler

At this point if you can't find that picture, 1QwkSport2.5r, not to worry, I take your word for it. I have a pension for the odd engines, already accumulated steel sleeve / iron piston ones, have engines using plain bearing aluminum crankcase without bronze sleeve, etc. They were good solid engines but need to be treated right. The Sportster is my most recent acquisition, but for a cause, mainly CL. I tend to keep my stuff for a long time, so they definitely will not be abused by the fuel.

1QwkSport2.5r

I'm an engine nerd myself. Self proclaimed of course. Treat 'em right and they will last forever if its an Enya, nearly forever if anything else.. Well, almost.

Happy modeling!

1QwkSport2.5r

Just because, here's the photo I was searching for. The fuel is Odonnells Race 30% nitro car fuel and the oil is Klotz Benol.

Photo courtesy of RCU member llkoolskillet.