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

Eng mod?

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Old 10-11-2006, 07:30 PM
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streetrodder
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Default Eng mod?

My club is trying something different we are using vipers and predators with super tiger .40 and os .40 fx, we use stock mufflers with the baffle removed aside from fuel and props what is the best engine mod we can do. We are aloud to preform any mod we want as long as it is not swapping the piston and liner out. Several guy talked about removing the shim out from under the head but is there more we can do. Thank you
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Old 10-11-2006, 07:44 PM
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skull1971
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Default RE: Eng mod?

Change carbs, open up the muffler, polish the intake runners. If you remove the shim, you need to limit the nitro, higher compression = hotter combustion chamber, and stuff starts to melt. I have a book about 2-stroke tuning, if you want I can send the information to you.
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Old 10-11-2006, 07:46 PM
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Please send me more info send it to Spoony46@hotmail.com Thank you
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Old 10-11-2006, 07:50 PM
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Default RE: Eng mod?

Dont remeber were i saw this but im sure you could make yourself a "turbo" simply make a metal funnel that bendsforward from the crab this should shove more air nto the motor and give you a couple extra rpms never tried it but i dont see why it wouldnt work
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Old 10-11-2006, 08:00 PM
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glowplug50
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Default RE: Eng mod?

The OS I don't know.
The tiger needs all of the openings on the engine that might suck air rtv'd to seal them . Base of carb, rear plate, head, needle valve assembly where it fits into carb. Break them in with a cut off prop running very high rpm but rich on the needle. Try to find the old stlye tiger nuffler. If you can find an old needle valve aasembly with the shaved sides use that. It allows more air into the venturi. Make sure the needle valve assembly is aimed correctly into the crank opening. Basic stuff.
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Old 10-11-2006, 08:06 PM
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streetrodder
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Default RE: Eng mod?

Glow plug when you say make sure it's aimed correctly the spray bar should be aimed directly into the eng?
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Old 10-11-2006, 08:18 PM
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glowplug50
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The spray bar can be rotated 360 degrees in the carb housing. There is a ******l shaped opening in the spray bar that should be aimed directly into the opening of the crank. This will be down and slightly rear. The opening is not visible from the top of the carb. If the carb is off of the engine the opening should be centered in the opening if viewed from the bottom of the carb.
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Old 10-11-2006, 09:06 PM
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skull1971
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Default RE: Eng mod?

That is more a velocity stack, but they are tricky, and I don't recall one on a 2c engine. 4c yes, and if tuned work very well.

Here's a question for ya, Why can't you turbo charge, or super charge a 2 cycle engine?

Before someone tells me I stupid, Detroit Diesel Engines are excluded from the above question, different theory of operation. [>:]
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Old 10-11-2006, 09:09 PM
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streetrodder
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I don't think they make a spool small enough for a .40 2 stroke but a good Idea!!!!!!!!
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Old 10-11-2006, 09:17 PM
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skull1971
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Default RE: Eng mod?

LOL, , Yes it would be very small, but think of how small the r/c jet spools are. But that's not it.

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Old 10-11-2006, 09:21 PM
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Default RE: Eng mod?

Skull, How are you polishing your intake ports ther is not much metal in the block are you also dressing up your liner?
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Old 10-11-2006, 09:29 PM
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glowplug50
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Default RE: Eng mod?

You can also polish a new ring on some glass with some jewlers rouge.
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Old 10-11-2006, 09:32 PM
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Default RE: Eng mod?

Rodder, its a matter of perspective, to me there's all the metal in the world. You don't want to remove lots of metal just make it smooth. The area under the carb is not real important because the crank is there, and transfers the air/fuel mix to the bottom of the cyl, and that is a mess of "Upset" air. Polish the runners along side the liner, and yes you might dress port on the liner too. Remove all casting flashings.
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Old 10-11-2006, 09:33 PM
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Use a figure 8 pattern
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Old 10-11-2006, 11:08 PM
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ORIGINAL: skull1971

Change carbs, open up the muffler, polish the intake runners. If you remove the shim, you need to limit the nitro, higher compression = hotter combustion chamber, and stuff starts to melt. I have a book about 2-stroke tuning, if you want I can send the information to you.

If you can without too much trouble can you send me two stroke tuning info, thank's in advance. branta335@earthlink.net
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Old 10-11-2006, 11:21 PM
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Default RE: Eng mod?

Except for what glowplug50 told you, the rest is simply a waste of time. If you are allowed to make any mod's to the engine, you can do far more by changing the timing of the intake crank and the sleeve timing. Turning down the head (so it moves closer to the piston allows you to do things like adding shims under the sleeve to raise the exhaust port for higher timing. The fit of the bearings is also important for performance. Most sport engines don't have the bearings fit correctly. When done right, there should be a bit of "end play", which means when the engine is running, all the thrust load is held by the rear bearing, and the front bearing is floating with no axial load.

Make a degree wheel to start with and find out what the engine's timing is to start with. Then do a bit of research on 2-cycle timing of different RC engines.
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Old 10-12-2006, 01:55 AM
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Default RE: Eng mod?

HighPlains, I have to, of course, disagree with everything being a waste of time. One of the most important thing in the operation of an engine is air. The smoother the path for that air the better the chances are the engine will produce power. Yes I do agree the changes in port timing will help, but putting a shim under the liner to "Raise the exhaust port timing" I, again, disagree. If you shim the liner would you also raise the intake ports too? what would be the gain? Plus you move the combustion chamber farther away from the piston crown, thus lower compression. Not everyone has access to a machine shop to turn a ST into a Jett or a Nelson, but most everyone has a Dremel tool and a buffing wheel, and it's not what you take out, it's what you leave in that's most important.
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Old 10-12-2006, 02:00 AM
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Default RE: Eng mod?

Gentlemen, the book I spoke of Two-stroke Tuner's Handbook by Gordon Jennings.
ISBN 0-912656-41-7

It's an older book but the theory is all the same.
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Old 10-12-2006, 04:27 AM
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Default RE: Eng mod?

I have been meaning to ask around about what some approx. timing figures might be...a range you might say, for a modified sport .40 like an O.S. .40SF for example

I have experimented on the outside of the sleeve, but haven't done any port timing alterations yet.

I have a ringed .40SF, and I figure I can do some experimental work on the port timing w/o worrying about chrome or nickel peeling.
The sleeve is very thick...think it's the same O.D. as the .46, just a smaller bore?

The crank induction passage is very large (for a .40 ) in this engine, I think because it's also the .46's crank, except maybe a slightly shorter stroke, so that's not gonna be a restriction. Got a decent carb on it too.

HighPlains...ya got any Key words to search for when looking for approx. timing #'s for our little 2 stroke model engines? I looked around, but got nuthin' (yet )...must not be lookin' in the right place?
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Old 10-12-2006, 07:49 AM
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Default RE: Eng mod?

Plus you move the combustion chamber farther away from the piston crown, thus lower compression.
Turning down the head (so it moves closer to the piston allows you to do things like adding shims under the sleeve to raise the exhaust port for higher timing.
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Old 10-12-2006, 11:48 AM
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Default RE: Eng mod?

What Highplains is talking about with shimming the head, is pretty much the norm for getting more power out of the OS 46AX for racing. Not legal to do ,but is done by a lot of guys cause they know that their engine isnt going to be inspected at a normal club round.

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Old 10-12-2006, 05:08 PM
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Default RE: Eng mod?

I see, but that goes back to not everyone having easy access to a machine shop. Thank you HighPlains, crasharama, for your time and input, and everyone else. I'm going to get one of these ST's and fiddle with it and see just what can get out of it. HighPlains, what fuel would you suggest for this engine and application? The standard PowerMaster 15%?
Again Thank you for your time, and of course, I mean no disrespect. ERIC
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Old 10-12-2006, 05:53 PM
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Default RE: Eng mod?

High planes where do you find timming numbers and also how much do you recomend taking off the cyl head?
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Old 10-12-2006, 05:56 PM
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Default RE: Eng mod?

Here is something to get the words flowing. 15 % is great. Do yourself a favor and leave the castor at the hobby shop and run straight synthetic in every engine you own. The engines will love you for it.


Smile
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Old 10-12-2006, 07:17 PM
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I agree with the synthetic. I have a few questions on the timing. I understand how a 4 stroke works as far as changing timing both mechanical and electrical.(PS I'm a Chrysler tec of 12 yrs yes still a young pup)Now as far as a 2 stroke I can not measure with a dial indicator when the valve opens and closes is it done by eye am I looking at this the wrong way or what someone please explain a little for me . Thank you[sm=what_smile.gif]
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