jayseas

WOULD THE SIG 35% NITRO 1/2 CASTER 1/2 KLOTZ FUEL BE TO MUCH NITRO TO RUN IN COX .049 ENGINES?
JIM

robotfan

My Feedback: (14)

Define "too much". Sig 35% is not too much because guys at Whittier Narrows use up to 60%. But the engines wear out more quickly than the guys who use 25% or 15%. But using 25% or 15% does not produce as much power or speed. So if you want your engine to last longer, 35% is too much. But if you want to fly faster,win races, or pull a bigger airplane, 35% may not be enough.

You'll know you're really using too much when the piston falls apart.

R Bush

My Feedback: (73)

Also, as you increase the nitro content, you may need toadd head shims to decrease the compression.
As a guide, I've heard the old Cox Racing fuel was 30%.(?) Somebody please correct if you know.

Randy

jayseas

I THINK YOU ARE CORRECT NOW THAT YOU MENTION IT.MAYBE I WILL JUST USE THE 25%.

paw080

Hi Jim, using 35% nitro fuel all depends upon your application and even which Cox engine

you are using. If you are flying in FF contests, old school TD Combat or Mouse racing;

then yes, 35%-40% is great to use. You will have to pay attention to deck clearance.

The higher the Nitro %, the more clearance you need. .012" is safe for 30%-35% Nitro.

.012" head space(TD .049) is what I used when flying 1/2A Combat decades ago, and

this was safe enough to last at least twenty 24,500rpm(ground rpm) Combat flights; so

the reliability was there.

If you are sport flying, then 25% Nitro fuel makes more sense, just try to watch your

deck clearance and prop load....a 5" X 4" is too great a load, even on TDs.

This brings up an additional point. Most 1/2A competition flyers, started with an engine

that is setup to blueprint specs as much as possible. Foremost is setting the cylinder

height with cylinder shims(NOT PLUG shims), still available from an ebay source. The cylinder is shimmed

up so that the piston top at TDC is exactly even with the plug shelf. then the TD plugs

are selected so that with plug shims, you acheive the desired head space.

This gets tricky because you must include the distance between the bottom of the plug

up to top of the squish band. What makes this weird is that this squish band measurement

varies a BUNCH because of mfg tolerances. Sorry for the Tome..

Tony

jayseas

TONY, THANK YOU FOR THIS INFORMATION, IT WILL VERY USEFULL.

Hossfly

First I no longer run Cox .049-.51 TDs, .074 (without running to workshop I think that is the right size) and any of the HOT engines. I ran the TDs way back in '50s and '60s using regular cox fuels when I flew FF and 1/2A proto speed.
Now in this time period I do every so often take down some of my many-year-old self designed 1/2A Cox .049 CL models in the 20-22" w/s profile and small fuselage models to fly with some of the kids around. Some 15 years or so ago, a good engine person in a model magazine now gone for years wrote that many small engines were expected to need lots of nitro. He said that 10-15% nitro was good for sport running and what was needed was more castor oil as small engines needed more lubricant than normally provided.
I now fully believe what he said is true. These Cox .049s are so easy to run well when I went to using regular 10% nitro, 18% oil RC fuel with enough castor oil to bring the oil up to 25%. Start easily, fly steady runs and no problems sometimes not having been run in over a year.
So depending on what you are after will certainly make a difference. Just thought that I would bring this item to light because it works very well for me. Good luck!

stuntflyr

Cox (red can) Racing Fuel was 30% nitro. The Sig 35% nitro is what I use in all of my .020's, .049's and .061's. I've used stock low compression heads with one thin shim, one shim and high compression heads, Tee Dee cylinders and high compression heads on Babe Bees, they all run great on it. 35% nitro isn't high enough to change much except make a little more power, tame the needle to make it less sensitive, and allow better starting and a little higher temp so it keeps the glow head lit.