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Old 06-04-2003, 07:28 PM   #1441
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Stefan,
That is a correct assumption.
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Old 06-04-2003, 07:37 PM   #1442
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Old 06-04-2003, 07:41 PM   #1443
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slobba
generally if that were the case the piston assy would be probably be slightly underweight. Its about a 65% ratio of the rotating mass.(piston, pin,clips and a percentage of the rod weight yeilds this percentage) however that method of balancing would yeild a false result. Balance is also effected by more factors than just reciprocating mass forces on the engine. There is also the firing force that occurs in the engine that effects balance. It is referred to as second order vibration. optimum balance is nothing short of a compromise and every scenario of fuel, power produced, and desired RPM must be factored in. It is not easy to scientifically calculate an optimum balance short of using a fixture and taking a physical running measurement of vibration in the XYand Z axis and adjusting accordingly the balance percentage.

You will notice that engines I have done do not have insane carving done to the crank, especially the counterweight as in most engines the counterweight mass is to low to start with. Although if the mass were there or could be provided some extra windage work on the crank can be beneficial.
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Old 06-04-2003, 07:48 PM   #1444
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Thanks Dennis.

Could you probably give me a short inside on the differences between S1, S2 and S3 and parts interchangeability?

I looked at the NR website but couldn't find anything.

Thanks again,
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Old 06-04-2003, 07:51 PM   #1445
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Quote:
That is why the top fuel engines have dual plugs, since Nitro is so slow burning and there are such high pressures inside those engines a single plug would literally just be blown out like a candle.
Ronnin
while what you say is true, the additional reasons that they are using dual plug in Top Fuel engines is that the fuel volume being injected into the engine is so high that one misfire leaves enough residual fuel in the cylinder that upon the next cylinder filling the engine cylinder literally hydrolocks lifting the cylinder head off the block with a big bang. The ability to have an ignition system that can fire that rich a mixture gives them an advantage that you cannot get with a glow plug. At the F/A mixtures those run a glow engine would stall and die being way to rich. the thought process was the same with multi plug on a glow engine but without an actual high powered ignition system it became a non advantage. So why not an ignition system? One has not been devised that will accuratly fire at that RPM on a Two stroke. Remember a 4 stroke engine only fires once every 2 rotations. 10,000/2 = 5000 strikes per minute. 20,000 is about the limit that has been designed
A two stroke would be 26000=26000 per minute etc

Slobba
Quote:
there are spots that are richer and leaner than the mixture that is coming from the carb.
This was an issue to and is an accurate assumption.

Quote:
hence the 2nd plug to help promote ignition timing to happen when it's supposed to.
This was the thought process. It had mixed results.
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Old 06-04-2003, 08:16 PM   #1446
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There are just a few things you need to look for when interchanging parts between all Novarossi type 12 engines. hopfully this will dispel some myths or inaccuracies that have been posted around the web.

Covers the following engines in rear exhaust design with the exception of the new RBV12.
Novarossi,RB,Novamega,HPI,rex

The piston and sleeves and rods

will all interchange including the 5 port designs with this exception. The MT/REX 12 can accept all piston,sleeve and rod assys but all the others (short rod)cannot accept the MT/REX piston sleeve and rod assy. the piston does not have a skirt or cutout and it will hit the crank. All novarossi's have 4.5 MM exhaust port heights and the physical timings are the same on the sleeves from model to model.

Head assys
will all interchange including turbo assys but the head finset must follow the head button.

All carbs will interchange.

All bearings will interchange, the V12 is an exception here

All backplates will interchange

Crankcases will all interchange except the MT/REX 12 the case locates the liner higher because it has a longer rod.

All cranks will interchange. The timings can vary from the wide intake design and the narrow. The wide design pops up from time to time and is relatively new. The MS Novamega 12 has it as does the S3.

The V12 crank is an exception here it is all by itself

ATTENTION
There is no long and short stroke Novarossi 12 crankshaft contrary to popular belief. Only a long and short version of the connecting rod and this has no effect on physical stroke.

All of them are 14 MM stroke/13 MM bore

There are variations of all these parts but generally the physical geometry is the same.

The side ports share parts with the MT/REX except one wierdo that was made by HPI (not the C12) that was a short rod side port

That's the jist of it
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Old 06-04-2003, 08:32 PM   #1447
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I took the case and crankshaft from my T5 S1 and added the rest of the engine from my RB 3-port. The engine seemed really poor on pick up regardless of how we adjusted the needles and top end wasnt as good either. We swapped the carbs and put the T5 carb back on and the engine went great.

On inspection I didnt notice much difference in the carb other than the body was wider at the mid needle end and the Main needle was positioned slightly differently.

I was thinking the wider body on the RB carb would be causing the problem with a different fuel entry timing. Would this be correct?
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Old 06-04-2003, 08:42 PM   #1448
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carburetor performance can vary wildly with Idental carbs and carb hardware.

One thing I can say with confidence is that no 2 carbs are alike. there are good ones and bad ones. There is a great amount of performance living right in the carb. when you find a good one mark it and hang onto it. The airflow around the slide valve and over the needle along with how well the midrange valve atomizes the fuel is a really big deal. A whole industry spawned for big engines based on this very premise and dyno numbers don't lie. It is a whole science by itself.

It is more than likley the slide valve raduis entry and the way the air flows over the Midrange valve and the valves propensity to atomize coupled with the venturis ability to accelerate the air down the throat than anything else. Hence the reason my carbs are not done like a JP
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Old 06-04-2003, 09:03 PM   #1449
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Thanks for the reply.

By the way. I can relate to the fuel consumption and pain in the pocket of running the bigger engines. We fly giant scale and I have a Super Tiger 4500 2-stroke (45CC) which can go through a gallon + of 10% every week easy depending on the usage. Just glad it doesnt go through plugs the same.

The costs of keeping it running are so high here that we now have a couple of 3W 80CC 2-stroke gas engines which we use for Giant Scale.
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Old 06-04-2003, 09:09 PM   #1450
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I heard that.
Them twin 90 riggers eat two 16 oz tanks of 50% in five minutes. 32 ounces a run. the carb measures over .510 through the bore. It had been a long time since I had the head off one of those so I dismantled one the other night. My god what a big son of a gun inside. All piston and sleeve. I guess I've been looking at 12's to long now. LOL

Hey man didn't anyone tell you guys that when they get that big your suppose to be able to get on it and ride it!
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Old 06-04-2003, 09:23 PM   #1451
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I agree. When you tinker with a .12 most of the time and then open up one of the big babies you feel like your in heaven.

We have been told that a few times about the big planes. A while back I even joked that I was going to build one with a special cockpit to hold my toy poodle dog. (The dog is cute for my son to play with but I prefer and used to breed Rottweilers).

My current project is a 240" wingspan Piper Cub to true scale. All hinges and the undercarriage have to be home made and I am looking forward to hearing the purr of the 3W 150CC pulling it through the sky.
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Old 06-04-2003, 11:12 PM   #1452
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It is referred to as second order vibration. optimum balance is nothing short of a compromise and every scenario of fuel, power produced, and desired RPM must be factored in.

Does that mean if you use 30% nitro, you would want the piston assy heavier than 65% compared with 15% nitro becasue the firing power is higher?

Also if you mod a engine, you want to know what fuel they use before to balance the engine or balance is not a big deal?



You will notice that engines I have done do not have insane carving done to the crank, especially the counterweight as in most engines the counterweight mass is to low to start with. Although if the mass were there or could be provided some extra windage work on the crank can be beneficial. [/B][/QUOTE]


I just bought the MAX 12 and the counter weight is very small compare to the previous, Does it mean , in that area, not as good? I always thought the lighter the better.

Thanks in advance
Chris
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Old 06-04-2003, 11:17 PM   #1453
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Quote:
Originally posted by kitracer
It is referred to as second order vibration. optimum balance is nothing short of a compromise and every scenario of fuel, power produced, and desired RPM must be factored in.

Does that mean if you use 30% nitro, you would want the piston assy heavier than 65% compared with 15% nitro becasue the firing power is higher?

Also if you mod a engine, you want to know what fuel they use before to balance the engine or balance is not a big deal?



You will notice that engines I have done do not have insane carving done to the crank, especially the counterweight as in most engines the counterweight mass is to low to start with. Although if the mass were there or could be provided some extra windage work on the crank can be beneficial.

I just bought the MAX 12 and the counter weight is very small compare to the previous, Does it mean , in that area, not as good? I always thought the lighter the better.

Thanks in advance
Chris [/B][/QUOTE]

run in your engine yet?

Keep us posted on the performance. I have got one 2 but not sure when I will run it in a couple of weeks time.
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Old 06-05-2003, 10:24 AM   #1454
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Quote:
Originally posted by kitracer

I just bought the MAX 12 and the counter weight is very small compare to the previous, Does it mean , in that area, not as good? I always thought the lighter the better.

Thanks in advance
Chris
If I recall, the MAX 12 has a slug of heavy metal in the crank counterweight - at least that's shown on their web site pic's. http://www.active-hobby.com/j/next.html

Is this enough weight?
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Old 06-05-2003, 10:42 AM   #1455
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Quote:
Originally posted by Motorman
carburetor performance can vary wildly with Idental carbs and carb hardware.

<SNIP>

It is more than likley the slide valve raduis entry and the way the air flows over the Midrange valve and the valves propensity to atomize coupled with the venturis ability to accelerate the air down the throat than anything else. Hence the reason my carbs are not done like a JP
Hmmm . . . interesting . . so, what's the principal behind the JP carb shape.
I've always wondered how that soup bowl profile was supposed to work. It certainly doesn't look like any intake venturi I've ever seen, but I'm not in a position to argue with JP about it.
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