Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

OS25 - Modification Help Needed

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Old 08-19-2008, 06:04 AM
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fastfret
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Default OS25 - Modification Help Needed

Can someone recommend me where I can send some OS25 engines to for modification for increase rpm or speed. Used to had it done in Australia but had lost contact with him. At the moment my stock OS25 is reving only 16,000rpm. It would be sweet if the mod can achieved 18,000 to 19,000rpm.

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Old 08-19-2008, 10:19 AM
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Default RE: OS25 - Modification Help Needed

well for the cost of shipping and all it would be more cost effective to order a better engine like a Jett .35bse it will turn a 8x7 at 21,000. If still loking to run a OS give me a PM we get about 19,000 on a 8x7 with the OS25
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Old 08-19-2008, 01:08 PM
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Default RE: OS25 - Modification Help Needed

One thing comes to mind. If we are talking about the FX series, you can drop an SX .32 carb on it and that is good for some more power.
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Old 08-19-2008, 02:59 PM
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Default RE: OS25 - Modification Help Needed

I've never looked at a .25 and .32 side by side, but have spent time looking at the .32 and it is a very un-trick motor. There is some clean looking transfer channels and not much wasted space in the case. The timing events are pretty conservative. The parts fits are very good, it goes together like a $1000 hand gun.
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Old 08-19-2008, 07:07 PM
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Default RE: OS25 - Modification Help Needed

Since when does a Glock cost $1000? After all, it IS the perfect handgun.

<- (Tupperware lover)
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Old 08-19-2008, 07:40 PM
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Default RE: OS25 - Modification Help Needed

I quted the wrong prop on the 25 its a 8x6 not 8x7 at 19,000
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Old 08-19-2008, 07:43 PM
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Default RE: OS25 - Modification Help Needed

you could send it to Jett as a trade in for a BSE .90 FIRE engine!!!

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Old 08-19-2008, 07:46 PM
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Default RE: OS25 - Modification Help Needed

You can pick up about a thou with a slight change of crank timing if you are running light props.
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Old 08-19-2008, 09:12 PM
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fastfret
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Default RE: OS25 - Modification Help Needed

Well Guys, I would be very happy to put a Jett 25 on the plan but frankly what I am trying to do was to "CHEAT" on a club 20 race as we are restricted to a OS25. So I am willing to send my engine for modification internally and yet looks stock outwardly.

Regards
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Old 08-19-2008, 09:20 PM
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Default RE: OS25 - Modification Help Needed

well there you have it. now the secret is out. good luck.

david
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Old 08-20-2008, 05:55 AM
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Default RE: OS25 - Modification Help Needed

OK guys, this intrigues me. I've never heard of tweaking an OS25, which I assume refers to the older 25s. I have a FP25 and would like to find a use for it in my combat gremlin. To date I've been running GMS 32 and an ancient ASP 40 with tuned pipe.

What can I do with my FP to get more power out of it.....assuming that's possible.
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Old 08-20-2008, 07:26 AM
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Default RE: OS25 - Modification Help Needed

Stage I, Open up the venturi, scrap the muffler and run it on bladder with 7.5x6 props. Stage II would have you trim the piston skirt to unshroud one of the transfer ports [@ BDC], then grind a corresponding notch in the counterweight of the crank to unblock flow to this transfer port, then grind the closing side of the crank window to close at 60 degrees. While all this is going on, don't forget the friction that lots of contact with the crank bushing has.....you will want to cut a relief notch in the crank to minimize drag,[reduce contact area with the case] then polish the main journal so that the crank spins as freely as possible in the case. None of this is anything new, it's old C/L combat engine technique that was done before the Nelson engines came out RTF. Final power tweaking comes with trying out various deck heights to set the head at, the FP head should be opened up slightly to run higher nitro. Some combat flyers ran FP .40s as practice engines and they held up very well. The .25s were popular as well with RC combateers and they got a boost from running mousse can pipe exhausts.
An engine that is set up and propped like this should be able to pull 400-500 sq inches around on a clean plane pretty good. You can't get something from nothing, all else being equal the .32s will always have more potential for the same weight and size.
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Old 08-20-2008, 11:30 AM
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Default RE: OS25 - Modification Help Needed

http://www.rccombat.com/forum/topic.asp?TOPIC_ID=12522
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Old 08-20-2008, 03:06 PM
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Default RE: OS25 - Modification Help Needed


fastfret:

Combat Pig will always be on top of the best advice around. Knows from where he's talking. There are some ways to cheat fairly. Optomize yourself, practice, practice, practice. Learn where that engilne is happy giving you the most thrust for the rpm's its capable of, and needle it so you get the most out of it when in flight, not the ground. Keep a good plug in it at all times, you will see some replacing the plug every heat. Ballance your prop and spinner well, good for a few 100 rpms. Take a close look at your bird and see where you can reduce weight and drag. Do you have your wing saddle sealed, control surfaces sealed? There is a few mph. All added up and decent flying should put you on top. Learning how to get a good line around the pylons is good for 500 rpm or more. The winner is in your head and thumbs. There is a very good reason, usually a lot of them that the same guys are in front year after year. They are both good pilots and pay a lot of attention to detail. Practice your starts, go high as close in as your rules allow (reduces time-distance errors in judgement) and use the dive to your best advantage in innitial speed (assuming you are using the flying start). If you are having a hard time judging coming across the start time within 1/2-1 second, tuck in behind the best starter of the group and follow him in. Winning is not always the fastest airplane out there. Winning is being the best pilot out there with the smarts to get good starts and use every advantage available. You cant win every race, but you can win the majority of the races. Some airplanes respond in turning well with a little elevon in the ailerons. Copy what the winners are doing and do it better. There is such a thing as a "racers mental edge", but cant really tell you how to get there. A winning attitude is not "cocky" when you back it up. Are you a "mean" pilot where some fear to pass because your will (they think) put them into the ground? Would I do that? To be honest, in a heartbeat. We race to win. You can always be nice when on the ground. ENJOY
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Old 08-20-2008, 04:29 PM
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Default RE: OS25 - Modification Help Needed


ORIGINAL: fastfret

Well Guys, I would be very happy to put a Jett 25 on the plan but frankly what I am trying to do was to "CHEAT" on a club 20 race as we are restricted to a OS25. So I am willing to send my engine for modification internally and yet looks stock outwardly.

Regards

Why would you want to cheat to win a rules regulated race?? How embarassing would it be if you were found out??

I have no issue with understanding the rules and pushing right up to the blurry edge, but stay within the rules.

At some of our bigger contests, motors are tore down and inspected. I can't imagine how I would have felt if I had taken a dremel to the insides of my nelson at the Nats this year. Don't think I could have shown my face at another race.

Learn to build your plane to get the most out of it, learn to tune your motor and optimize your props, and learn to outfly the competition. Thats what it takes to win at racing, there is no quick and easy way to win.
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Old 08-20-2008, 07:24 PM
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Default RE: OS25 - Modification Help Needed

Good points Daven. Who would really want something that they really didn't earn?
We have a local club that does 1/2A racing and one of the club officers has his "stock" engines running at least 1000 rpms higher than the next closest racer, 2000 more than what the average stock engine puts out, easily. It was enough to keep me from showing up last year, even though I have a couple of modded engines that would [at least in practice ] blow their course record away.
Where is the satisfaction in doing that?
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Old 08-20-2008, 10:08 PM
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Default RE: OS25 - Modification Help Needed

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Old 08-20-2008, 10:24 PM
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Default RE: OS25 - Modification Help Needed

i wouldnt even mess with FP's if they have steel pistons. dont mess with timing unless you "really" know what your doing.
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Old 08-21-2008, 11:52 PM
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Default RE: OS25 - Modification Help Needed

Fastfret,

what airframes are you flying and what props are you using? is this the .25 FX?
this will determine where you want to start tweaking on your motor?

i dont recommend cheating to get the edge.

Read what Rmenke posted several times. They are great words of wisdom.
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