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

OS. Mod

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Old 07-27-2011, 05:49 AM
  #1  
aberry1917
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Default OS. Mod

Yes i am wanting to mod a 0s .40 engine i have as a spare and just see what it will do. I know it will shorten the life span of it alot but it is a spare and we would like to see one really jacked up fly once. I have a read in some forumns that some extreme mod folks can achieve 30,000 to 40,000 rpm for short periods of time. Can someoen direct me to a company that does these type mods? Or to directions how we could in our machine shop we own. Thanks for any help you may give.
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Old 07-27-2011, 06:27 AM
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Default RE: OS. Mod

NO SHOP CAN GET THESE TO RUN 30,000-40,000 WITH A FLYABLE PROP.

You can run it stock to that rpm. put a APC 5.5x2 prop on it. take off the muffler and then should be able to get close to 32,000 with it.

If you can get it on a 2 lb airplane with at least 400 sq " it should take off and do about 100 mph.
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Old 07-27-2011, 11:22 AM
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ORIGINAL: aberry1917

Yes i am wanting to mod a 0s .40 engine i have as a spare and just see what it will do. I know it will shorten the life span of it alot but it is a spare and we would like to see one really jacked up fly once. I have a read in some forumns that some extreme mod folks can achieve 30,000 to 40,000 rpm for short periods of time. Can someoen direct me to a company that does these type mods? Or to directions how we could in our machine shop we own. Thanks for any help you may give.

What specific OS 40 do you have? There are some things you can do to improve top end power but the cost of doing so gets close to buying an engine that has the performance stock

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Old 07-27-2011, 01:02 PM
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Default RE: OS. Mod

oh i am sorry it is os.40 LA.

andy
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Old 07-27-2011, 01:30 PM
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Default RE: OS. Mod

In that case the answer is easy. This is not an engine to modify. It is a plain bearing engine with small intake and very conservative port timing. It is not made for high RPM, and in my opinion would be a mistake to try to make it do what it was not designed for.

Scott Mooney
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Old 07-27-2011, 02:25 PM
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ORIGINAL: Pylonracr

In that case the answer is easy. This is not an engine to modify. It is a plain bearing engine with small intake and very conservative port timing. It is not made for high RPM, and in my opinion would be a mistake to try to make it do what it was not designed for.

Scott Mooney
Scott Mooney Racing Engines

It doesnt matter if plain bearing or not it can be made to perform just as good at the ball bearing engines. We take a TT GP 42 and get it to turn a 9x8 at 17,300 with jett pipe. the whole engine and pipe is 11 ounces. you cant beat that power to weight ..... lol.

If you really want to get more power out of that engine send me an email and i will give you the specs to do it your self. If you do i need to know what prop and exhaust you plan to run and what application.
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Old 07-27-2011, 03:29 PM
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Default RE: OS. Mod

The FP is not designed to be a performance engine. The TT is a bit better in terms of port timing and carb size. IMO the OP should look through the classifieds or E b** for a more performance oreinted engine
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Old 07-27-2011, 03:45 PM
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Default RE: OS. Mod

The plain bearings do not make much difference in performance, only in life. They wear pretty fast at extreme RPM. I stated that the la series has small intake and conservative port timing; perhaps I should have been a little more specific. The carb is quite small, and so is the front crankcase housing, making installing a larger carb quite difficult. The other problem is the intake area into the crankshaft and the port diameter through the crankare also quite small. I suppose you could increase the timing, but port area is still the issue. Making the port area larger means drilling out the crank, which is already pretty small. Youdo not want the crank to end uptoo thin. There just is not enough area to work with to make this a worthwile project.

Use this engine for what it is, they are very good engines.

Good Luck
Scott
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Old 07-27-2011, 07:21 PM
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Default RE: OS. Mod

I ran a few of these engines in 80 mph limit combat with 9x6 props and they are perfect for this application.
If you can drill out the crank and do some timing mods, you might get 100 MPH [8x6 @ 18,000 rpm].
I don't know if this engine can be worked to ".32 CVA" specs, but that's what you would shoot for.
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Old 07-28-2011, 01:22 PM
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i am sure if i can get the LA to spin a 9x* at 16,500-17,000 i can get it to spin a 8x6 at 19,000. you can take the stock carb and open them up pretty easily. many mods can be done. we have taken small carb engines designed a venturi for them. then milled a 1/16-1/8" grove on the inside of the case where the carb rests. dril 3-5 holes in venturi where the slot is and run a remote needle to get the hole big enough. need the carb to match the crank hole size.

If have a crank that can not be opened up then shorten the length of the crank runner.

Also sometimes bigger isnt better. you can have a high velocity that will carry more momentum which can pack more fuel air in. it is all a balancing act.

Biggest thing when experimenting is to make one change at a time then run it and then do another. when you no longer see an increase then stop. also if grinding ports go slowly and very little at a time. for the exhaust ports i have found that for most engines have the top of the port wider than the bottom. then put a taper on the port upwards 15-20degree angle.
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Old 07-28-2011, 04:56 PM
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Default RE: OS. Mod

With the intake ports enlarged to ingest more charge, wouldn't that put a heavier load on the bottom end, from the crank to the front bushing? I would think it easier to just go out and buy a schneurle ported engine and save the hassle.
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Old 07-28-2011, 05:04 PM
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Default RE: OS. Mod

Thats alot of work when you could just buy one of these


http://www.rcuniverse.com/market/item.cfm?itemId=766571

http://www.rcuniverse.com/market/item.cfm?itemId=766269

http://www.rcuniverse.com/market/item.cfm?itemId=764298
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Old 07-28-2011, 06:32 PM
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Default RE: OS. Mod

airrapator takes it for granted, that he has a natural aptitude for porting. Unless someone can magically acquire book full of knowledge and the gifted paws, the novice in all likelihood will build a small pile of paperweights before he has a screamer.....and that's all it may do, no idle, just scream.

This is a look over the mentors shoulder, do this but never do that, hands on type of thing. The subtleties of breaking one edge the wrong angle or champfer makes a world of difference. You got to have a plan and know why you are cutting, widening, raising. Everything interacts.

Remember, you can save the screws and recycle the aluminum when you are sick of looking at the paperweights
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Old 07-28-2011, 08:10 PM
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Default RE: OS. Mod

Well stated freakingfast. I have been building racing engined professionally for 20 years. There is a very steep learning curve to porting and airflow.I turned some expensive cylinder heads into paper weights early in my carreer. The flowbench is your friend and your enimy...

Best of luck
Scott
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Old 07-29-2011, 11:54 AM
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Default RE: OS. Mod

NOX
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Old 07-29-2011, 01:41 PM
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Speedracer makes my point, that is unless you want to really go thru the carving process which can be fun. I just look at the manhours involved and then I look at the Rossi posted at the forsale forum. BTW, I ran NOX in my '68 Roadrunner before I sold it. Scary to flip that switch until you get used to it.
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Old 07-29-2011, 01:53 PM
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Nice try guys, It is NOS not NOX. Close though.
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Old 07-30-2011, 05:40 PM
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No, actually we did refer to Nitrous Oxide (laughing gas) as just that, NOX. The acronym really didn't make a dif, but setting up the mixture to richen up when the tank was on did. Fun stuff.
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Old 08-02-2011, 04:47 AM
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You can always take out the carb. completely and just put in a needle valve in one side of the mounting hole an plug the other hole.  You would want a shutoff for a "throttle".  You can always shim the liner up .020" at a time and machine off the same amount from the top of the liner to experiment with higher powerbands and a pipe. (and still go back to stock.)  Radiusing  the rod to a teardrop shape and smoothing or polishing (almost), gives about 300 rpm and doesn't  adversely  affect the life of the motor if moderately done and not revved too crazy.  Lightening the piston from the inside can get a few more revs and not hurt the life either. I wouldn't port the inside of an OS because of the lousy plating.  The crank closing time could be delayed a bit for the higher revs to unload a bit in the air.  It cannot be reversed if you go too far though.  The turbo crank thing may help a bit but I couldn't measure the difference on a couple of .15's that I tried. These should give 1 to 2 thousand rpm and a pipe maybe another couple.  (or no muffler if there are no neighbors.  To save weight for a combat or free flight you could grind off the muffler mounting tabs but then there is no return to a muffler)  I am sure there are other ideas that I would like to hear as well.
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Old 08-02-2011, 05:54 PM
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My first question would be.....does the LA series use the same metalurgy as the engines in the high performance lineup...?
If not, then it's a waste of time to try to run a LA motor with pipe timing and other such grinding.
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Old 08-03-2011, 08:24 AM
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Aren't models just a fun waste of time?   I just took the backplate off one of my $15 LA .40 swap meet specials (broken needle valve and backplate, typical)  The piston looks pretty thick and the rod looks squarish, so lightening them would be beneficial, but the crank web looks pretty weak to me for modifying the crank hole too much for high revs.  It would make an interesting control line ratracer experiment but would likely break at a certain point. Our .15 LA motors ran a large 8" 4" prop on a control line combat and went  ok because of the conservative timing. The russian stuff use a 6" 4" prop and go only a bit faster really.  They sure sound good though. Good cheap motor to practise modifications on but I vote for the Rossi, Nelson, or pylon motors to really rock.
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Old 08-03-2011, 08:49 AM
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Default RE: OS. Mod

I will sorta agree with CP the OS LA engines are the hardest and worst to try to get power out of them but power can be had. All engines of simular size can be made to make the same power of other simular engines. The TT Gp 42 is a better canidate for mods.


general mods are to raise compression, open carb, square off crank intake hole timing in the 35-60 range, epoxy the front of the crank hole, angle the crank exit hole (dont do the turbo mod that the car engines have we havent seen any increase at our rpm numbers) raise the exhaust to around 160-170 for stock muffler or tower muffler type and 175-182 for 1/4 wave Jett style mufflers, and set the transfer at .100 difference for ever 20mm of stroke ie 10mm gets .050 and 30mm stroke gets .150. Squish is around .020 average.


The thing with all the mods while l=doing a new engine or learning is to do one mod then run the engine and then do another. For your exhaust timing grind a little at a time like .020 till getting close to 165 or so then down to .010 each time to see how the engine reacts. Exhaust port shape for general performance is to have the top wider than the bottom.

There is more that can be done but look at the engine measure every thing first then go to cutting. Start out on cheap swap meet engines or garage sale ones.
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Old 08-03-2011, 07:12 PM
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Default RE: OS. Mod

What is really helpful is to have a couple examples of factory screamer engines in your hand that you can study, measure and take ideas from. You can learn more in 1 afternoon from taking a Nelson apart than you could from years of trying things on your own.
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