djmp69

In my 20+ years of flying, I've come to notice that bigger engines are not happy with a lot of Nitro. .60s run great with 15%, but put that in my 1.08, and no matter what combination of low side/high side needle settings, including plug changes, that 1.08 doesnt run anywhere near as well as it does on 10%, and most perfectly on 5%. Now, I do have a .91 that I've gotten to run pretty ok on really rich high side 15%, even though the guy that owned the plane before me ran 10% and it ran like crap. So no ow I'm wondering if I can get it to run just as well or better if I drop to 10% and lean it to optimum... Or am I getting a better performance with a higher nitro percentage at a richer setting? As fuel is really expensive nowadays, I'd hate to buy a whole gallon of something that wont get the plane any faster.

any jdeas?

ho2zoo

My Feedback: (5)

I think you're right to use less nitro for bigger engines. I have an old Super Tiger 2000 2-stroke, which is 20 cc (I think), and it won't run worth a darn on anything higher than 5%. My 40s, 60s, and even 91 run good on 10% or even 15%. I keep a jug of 5% around to run that Super Tiger. It's on a 1/4 scale Cub and pulls it around just fine.

djmp69

Yeah, I hear you, and that's my question. My .91 (OS) is running 15%, way rich. I'm just wondering if I can get a little more speed out of it. Ground clearance is an issue so a bigger prop is no go. So I'm just wondering if dropping down to 10% and running more lean will give me more punch than rich 15%. Sure I could just try it if I had some 10%, but I'm not blowing that kinda money on an experiment, lol.

aspeed

Usually higher nitro needs a cold plug, and an extra shim in the head/cylinder basically so the plug doesn't blow. If you really want the power, that is the way to go. There is the price of course, so 10% fuel is what I use, I have noticed a gain even with 15% though on smaller motors. For your plane that you want to go faster, Pitch is the answer, not diameter. Leaner of course, but then land it if it gets too lean, to save your plug, and motor. 15% is not really that high of nitro content.

j.duncker

My Feedback: (2)

Compression ratio is the key factor. Many large European/ engines had compression ratios on the high side as they were expected to run on zero nitro or 5% as a max. Super Tigers, Mokis and MDS engines were typical examples, feed them 15 % nitro and they would overheat and run poorly just like an overcompressed diesel. If you wanted to get them to perform on 15% you had to lower the compression ratio with head shims.

rgburrill

More power. Grunt. Speed. grunt. Nitro. Grunt. Sound like Tim the Tool Man.

ho2zoo

My Feedback: (5)

I haven't had any problem running my 2-stroke OS .91 on 15%. Very reliable. And the .91 and 1.20 4-strokes run on 15% too. Just that big Super Tiger that needs 5%. But whatever they need to run well I guess.

djmp69

Finally, a real world related response.

dont get me wrong, there's been REALLY helpful responses here, its just that someone else with a .91 OS running 15% can offer some really helpful empathy.

what prop are you using? Are you running really rich? Are you shimming the cylinder head, or are you, like me, running 15%, no special tricks? Just trying to compare what you're using and experiencing to get an idea of different things I can try...

TomCrump

I run 15% in all my glow engines, from the .52s to my 3.00s. I do nothing special.

As stated above, the European engines are a different breed, and don't require nitro. I ran my Moki 2.10 on 0% nitro.

jester_s1

I am having trouble understanding why you wouldn't want to run 5% in your bigger engine. It's cheaper, which will make a difference in the long run. 5% will run just fine in glow engines made for the American market too (OS, Saito, etc). You may notice the idle won't go quite as low, and you may notice a small decrease in power. For racing or aerobatics that might be an issue, but otherwise it's nothing to worry about.

aspeed

For racing and speed events, in my circles, we are limited to 10% nitro, and it is supplied at the contests. In the US it is normally Sig fuel. When I fly anything it is usually 10% because I have it around. I will mix up some stronger stuff sometimes for the 1/2A planes. They don't use much. A cup full is enough for a while. Funny abut Tim the Toolman. I was a toolmaker and have quite a collection of tools. When I started flying in about 1969, the first time I saw another guy flying, I wanted to race. Our MAAC (like AMA) magazine was called "Competition Canada" Things change over the years. Fun Flies now, no competition much any more. Scale? Pylon is fizzling out in many areas.

djmp69

For that very reason, power and speed. I have an O.S. 1.08 that I run 5% in, and it's on an aerobatic plane. It's great. Yeah I fly it fast some times, but mostly aerobatics. But my .91s are on fast planes (F18, Patriot). It gets pretty annoying when other planes are walking past mine, so I'm just trying to get more power, more speed, "grunt grunt grunt".

ho2zoo

My Feedback: (5)

Ok, I have the OS .91 on a Top Flight Corsair. Uses a 14x6 APC or Evolution 2-blade prop. OS #8 plug, no shims or anything special. Wildcat 15% fuel. Not running especially rich. Since the engine is in a cowl I am using a Bisson pitts-style muffler and built the ducting to direct the airflow over the engine as was recommended in the build manual. Has a big opening at the bottom of the cowl to let the heat out. Runs great and I get a lot of speed, but it will only run about 9 minutes at full throttle. Can't fit a bigger tank in there.