Flyboywbl

Hey yall i was wondering if there are any mods i can do to my three OS 25 fx's (they are all on lanier slashers). I turn about 15,000+ with a MAS 9x4 and i'm at 4500 ft. I'm running byron fuel with 15% nitro and 20%oil. I've seen guys with these engines running 22,000+ RPM's. I don't know what there secret is but i wish i could turn that many! The only tools i have are your basic rc tools and a dremel. I'm willing to go out and buy any dremel attachment but i don't really want to buy any new tools. Can i acheave this awsome power? Please let me know If there is a website or forum that goes into detail with some mods i could do and pics would be nice to
thanks for all your help!
-Matt

RC MANIAC119

My Feedback: (14)

Matt............The first thing you need to do is take out the baffle inside the muffler! This is a simple fix that can add and extra 1000 RPM.

Loosen the nut on the backside first....before you attempt to remove the long retaining screw. When you have the muffler split apart you will see the baffle.........take it out, put the muffler back together, and don't forget to use some Locktite!!

Enjoy your new speed!!

Montague

What you want to do is remove the muffler and install a mousse can. The mousse can is a short tuned pipe and is good for 1,000-2,000 rpm, depending.

What prop are you using? The fastest turning props are the old Master Airscrew GF/2 props. APC and the new MAS GF/3s don't turn the same RPM for a number of reasons. For most flying the APC and newer MAS props are more efficient, but for hard turns, the "lower gear" of the old props work better. MAS still makes the GF/2 in the 9x4 size if you ask them directly and order a dozen or so at a time. That's where I get mine.

The fastest I've gotten an unmodified OS was around 19.5, on a mousse can with the above prop on 15% fuel. To go faster, get some powermaster fuel with higher nitro. I was using a mix of 30% and 15% to get 22.5% for a while, and that's good for at least 500rpm, maybe more. Some guys run straight 30%.

Play with glowplugs. When you start going to higher RPM, you usually want a colder plug. Also, the OS plugs are slightly short, which lowers the compression a little. I use the K&B 7300 plug, but there are plenty of other good ones out there.

Break-in really matters as well when you want top power. You really need to use a small prop and do a careful temp cycle break-in. And never, ever, run the engine "4cycle" rich, or at low throttle more than you have to. Cold running wears down the piston/liner fit and causes the engine to loose power at the top end. Not enough for a sport flyer to notice, but when you're going for peak power, it shows up.

Flyboywbl

baffle was already gone, thanks for the tip though. That was actually one of the first tips I got when i first started flying 7 years ago. Now i do it to all my two strokes. I've heard i can take the shim out of the head to up the compretion. I'm not alowed to fly a mosse can muffler at my club due to noise complaints. We all just fly the stock FX muffler.
thanks
-Matt

daven

My Feedback: (1)

Can you use an ultrathrust or jettstream style muffler?

That would help a lot!

rcfury

My Feedback: (5)

You can use the jett muffler if you want. Ive got a few members of my club who use them with great results. Its just expensive. Plus, when you are dealing with rc combat you really dont want to loose the pretty ultratrust muffler due to a midair. I have a moose can pipe that i made on my OS 15 with awesome results, and it lighter than the jett pipe.

RC MANIAC119

My Feedback: (14)

Get a MACS Muffler/tuned pipe for that beast....

yankee samurai

My Feedback: (175)

If you're concerned about noise the mousse can set up is actually quieter than a stock muffler. The Mac's black muffler offers little performance gain if any. I see you're from Bozeman do you know Phil Battle or Charlie Pfliger? They both attend my contests twice a year.[8D]

Flyboywbl

Yah i know them. Charlie taught me every thing i know pritty much. I just started combat last summer and know i have three lanier slashers. I think once i start crashing them beyond repair i'm going to start working on my own design. Anyway i think i will make it out to ID this year and get torn up. i'll probibly see you there.
-Matt

yankee samurai

My Feedback: (175)

Matt,
Come on down. Charlie can tell you how much fun it is. There are usually eleven Open B pilots that show up. I don't know if you know Ron Horton, he is from Billings and is getting back into combat. He told me he would be there. Plus pilots from Ogden Utah, Boise and Ontario Oregon, it's a hoot hope to see ya there.[8D]

Capn America

My Feedback: (3)

If you are limiting yourselves to stock mufflers, you are not going to see a lot of rpm. You can up the rpm by drilling the outlet on the muffler to a larger size. It will pick you up some more rpm, only good for wide open runs though as it also decreases backpressure that creates your fuel pressure.

flyinrog

My Feedback: (1)

Not big in combat, but you guys keep talking 1 to 2k increase with muffler stuff,,this guys talking about a 7k improvement 15 to 22k ..there has to be more than exhaust to this!!..porting,props,nitro?....Rog

Montague

Rog,

I think part of it is the prop, as in my earlier post.

And part of it is break-in. proper temperature cycling break in with a small prop can make a big difference in top end RPM.

And frankly, I've never seen an OS FX hit 22k. I have seen 19.5k on a stock OS.

One way to get more power is to replace the carb or drill it out. An OS .28 or .32 carb along with the tuned exhaust is a big improvement.

You need to get more fuel and air in, and more exhaust out. It's really as simple as that. So, larger carb throat and tuned exhaust or less backpressure on the exhaust.

However, opening the carb throat and messing with the muffler will make the mixture settings a lot more sensitive and make the engine "peaky". OS engines are known for having a very easy to set needle and strong fuel draw. All these mods will make the needle more critical, and will make it harder for the engine to draw fuel, so your tank setup will have to be more critical. The tank issue is why some guys use bladder fuel systems which provide fuel under pressure. Personally, I don't think they are necessary since you can get plenty of power using a stock tank, stock engine, and mousse can. That's all I do.

The Internet Killer

Drill out the carb ????

Any recomendations on how much to try ??

dennis

My Feedback: (90)

Actually drilling out a carb is the pits. If a reliable idle is not required but a carb is necessary then go for the largest one that will fit in your case opening. otherwise a large venturi with a shut off is better. Next forget about an idle and also forget about muffler pressure. Run a bladder or tank pressure. If you are into high nitro then you don't really need ultra high compression ratios as you'll have a problem with preignition and busted crankpins or rods. You need to become knowledgable about barometric pressure and shim the head for the days activities and use the appropriate amounts of nitro. Thats if you really want optimum conditions. Most casual flyers won't do that. Also forget about large props. Get rid of those 9 inch jobs. Your now playing with either 8 or 7.5 props you also have to find the best pitch for your particular plane. Also you really don't expect this motor to last you all season do you.
If getting a motor to go fast was easy then everyone would be doing it. It requires time and effort and maintenance of the equipment. The consistant winners are those that know their equipment and know what it takes to get the most out of it. There are really no instant cures for lackluster performance. But the ability to spend some time working with your motor and being willing to ruin a few of them will pay dividends in the long run.
Dennis

Razorback58

My Feedback: (8)

I'm trying to find out what is the biggest carb that will fit the .25FX without modifications. Does anyone know? I want to go with a bigger carb on mine and need to know what will be the best alternative. Thanks!

yankee samurai

My Feedback: (175)

Carb off an OS .32 will fit and has a larger bore.

The Internet Killer

You can try going to an online hobby website, (cough, tower cough) use their parts list
to locate the O-ring that goes on the base of the carb and then just check the parts usage
to get a list of all the carbs that use that O-ring, there is a good chance if they use that
O-ring they should/might fit .

Just an idea.



Edited for grammer, eh ??

Razorback58

My Feedback: (8)

Thanks Randy!

Toni Arte

I just discussed engine tuning last weekend after the Vaasa combat competition (ACES Finland). The Finnish champion said that the different glow plugs really make a difference, he has tested various Novarossi plugs, and basically the lower the number, the higher it revs.

We have limited tuning options, as our rules bans all tuned pipes, including the MVVS minipipe. On the other hand, it's good to be competitive with stock OS .25FX, or even with the cheap Chinese GMS/ASP etc. ball bearing engines.

Montague

A quick look at the Novarossi page seems to show that the lower number plugs are hotter plugs. If you are running the engine stock, with low nitro and a muffler, it makes sense that a hotter plug will lead to more RPM. However, on a mousse can or mini-pipe, or if you've run up the nitro, you might need a colder plug to avoid pre-ignition.

combatpigg

My Feedback: (3)

Lighten all moving parts inside the engine, pay attention to friction and decrease case volume. You can do some of this with a dremel and carbide cutters, but it is better to start out with machine shop experience. In the meantime, installing a C/L venturi and MCP is something anyone can do.

OzMo

My Feedback: (3)

the guys montague gives his streamers to have been doing the macs pipe mouse can deal for a long time its cheap and easy and it works well. most r/c flyers should probably refrain from internal changes without experienced guidence (IMHO). the replacement carb idea has a lot of merit though. look on FLEA Bay FOR burned out 32s BUT DON"T PAY TO MUCH!! its hard to toast the macs pipe and the cans are cheap

Razorback58

My Feedback: (8)

Is the 32 carb a direct bolt on replacement, or does it need to be milled down to fit? I've been trying to do a little research on it and from what I've been able to gather it looks like the .32 is about 3 or 4 mm larger than the .25, or am I looking at the specs wrong?

vertical grimmace

My Feedback: (1)

The .32 sx carb is a direct drop in, swap. The thoat of the venturi is larger. This will give you more power but remember you are reducing the engines ability to draw fuel. It may go lean in tight manuevers and muffler pressure will be mandatory. I have not flown one set up this way but I have run one once.
To purchase this carb plus the cost of your .25 you may be better off with the .32 in the first place. I wonder what your objective is? What plane are you going to put this powerhouse on?