I have an os .25 that we race pylon with. I am currently running 15% nitro in it.
Would it hurt it to run 30% heli fuel through it ? Would I have to do anything thing to the motor to do this?

Should I expect a big gain in top end RPM with 30% ??? IF so what? 500 RPM??? 1000RPM ???


Thank you in advance

Probably a waste of money. If it's a plain bearing sport engine it is ported for milder fuels and you probably won't see much of a gain.

You will have to open your needle valve some.

To gain much you will need to run a smaller prop

I plan on running a smaller prop. What is the advantage of a smaller prop?
I was going to go smaller and pitch it higher????

More RPM equals more combustion cycles equals more power

More nitro seems to do better at higher RPM

w8ye,
sounds like a good plan. I will get some high nitro and smaller props and start taching.
maybe I will get the results I want.

MORE SPEED.

See if you can get a eyeball on what the others are running?

They are running 20%. I saw the jugs. and they are running the same props as I am.
I stepped down to a smaller prop to spin faster, but the needle becomes unresponsive. you can crank it almost closed and it has no effect on the motor. I presume it does not have enough load ??

Something like a APC 7.8 X 7?

That is the exact prop they are running. Nothing gets bye you W8ye. you know your stuff
I was going to step down to an APC 7x8. pick up some revs and more pitch.

When going up in nitro there are usually diminishing returns. To go to 30% from 20% will not gain the difference that changing from 10% to 20% did.

One other thing you could do is start running the new multi viscosity Cool Power or S&W High Rev Fuel with
New high-performance synthetic oil. The oil is thinner in these fuels and you gain some rpm.

http://www.morganfuel.com/cp_mv.htm Right now it only comes as 15%

There also is a Cool Power 30% Heli with the thinner oil oil....

Keep your fuel in a different jug so they really don't know what you are running? Keep your fuel covered from the sun regardless.

GREAT advice.

Thank you!

BTW i think I have some empty 5% jugs hanging around!

I used to race 25 pylon (and 40) for a few years. We all used OS FSR or SF engines (stock), 15% nitro, 8x6 APC on Scat Cats. Our engines would tach at about 16,500 if I remember correctly. Three pylons, 4 planes at a time, fast and fun. The real secret to winging however always came down to smooth flying -

You never said what engine your are using. OS made several 25's.

Guys here are running OS25FX's and KY Mousse can mufflers with 8-6APC props. Great combo. Many are now using 30% fuel, but the actual measurable power gains are very small. 100-200rpm. Every little bit helps, but the power diff on this set up isn't worth it.

Fly better, shave off ounces wherever you can and you'll win more. 30% won't do it for you.

You will ruin your engine quickly with synthetic fuel with no castor [:@] It will gain RPM for a while, but it will wear quickly and soon you will end up with a lower RPM that you have now. Its not worth it unless you are racing on a big level for money and dont care about your motor.

JettPilot

It is the OS 25 FX

The Kentucky Mousse can muffler (Flying Z hobbies) is the "hot" add-on for the .25 OS.

That adds a lot of performance all by itself. The 30% nitro is by way of comparison adding very little to the result.

You can use straight synthetic with no problem. Just remember that it doesn't tolerate a lean run like castor oil does. With High nitro and running it fast, one lean run can toast that little plain bearing engine. If you run it at reasonable rpm with mild nitro synthetic will work fine. There are no bearings to rust.

The .25FX is a ball bearing engine. The FP/LA's are plain bearing. The OP states this is an FX engine.

Whoops didn't see that it was an FX. Thought he was running an FP. Synthetic is still Ok as long as he doesn't have a lean run.

Ron,

Did you modify the SCAT CAT to go faster? I have heard about cutting down the wings and the horizontal stab to make it faster?

Getting the compression ratio and plug right is the key to geting more power with more nitro.

You need a lower CR with more nitro and may need a cooler plug.

Add a head shim and play with different plugs. Guesstimate your airborne RPM and ground run with a smaller prop to achieve that RPM

You will not get massive increases 100 - 200 rpm. If anybody tells you they got 1000s then get the salt cellar out.

No, we did not modify the Scatcats. Part of our rules were stock plane and engine. Almost all used the OS 25 SF although I used the FSR. We all used 15% fuel and 8x6 APC prop. The planes were fairly quick and a lot of fun. As I mentioned before, the real key to winning was smooth flying that comes from practice -