RE: were to find a turbo or supercharger kit

RE: were to find a turbo or supercharger kit
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RE: were to find a turbo or supercharger kit - 10/18/2006 2:05:31 AM

supertib

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quote:

ORIGINAL: SAVAGEJIM

Pressure ia not density, but pressure IS required to increase density; it is not a byproduct, it is an integral component. Given an ambient pressure, if you want a given volume of gas to be denser, you will have to do two things: cool it or presurize it. You MUST have pressure to obtain a higher density given a set temp and ambient pressure. In the case of forced induction, PRESSURE is required to get more density. You can cool the air (like an intercooler for some tubocharger and supercharger set-ups) too, but cooling the air for a nitro engine is totally impractical.

Straight physics: P1V1=P2V2.
This is translated as pressure1 times volume1 is equal to pressure2 times volume2.
Density is mass per volume. To get increase density, you need pressure to squeeze more air mass into a given volume. Take that pressure away, and density will reduce back to its equilibrium state (i.e. ambient pressure and ambient density).
This formula will not work without pressure at all.

Now, I'm not a fluids engineer. This debate has really made me think and now I am inspired to learn more about the fuild dynamics than what I already know.

The pipe question again. As I said before, the increased pressure and volume of gas entering a fuel pipe when the supercharged fuel/air enters the pipe will do a number on the harmonic resonance in the pipe. The resonance will either be agvanced or retarded (phased) out of syncronization with the engine's timing. The supercharged fuel/air miture will definitely epend some of its energy into the pipe as the 16PSI (I'm assuming 16PSI boosted charge) back down closer to ambient pessure. The pipe will retain and provide back pressure as it is intended to do, but more gas will be pushed out the stinger, even with the harmonic resonance of the pressure wave in the pipe providing back pressure.
To get the backpressure you are mentinong a pipe will have to make forced induction to work properly, you will have to choose a different pipe. The stock one will not work, nor similar pipes for the engine in question. These pipes are designed to generate their harmonic pressure resonance for naturally aspirated engines. I am guessing you will have to use a more flow restrictive pipe to help offset the increased pressure of a supercharged fuel/air miture.

You built 4stroke race engines with forced induction; you therefore know that the cam profiels are different for that of a naturally aspirated race engine.
Now, nitro engines do not have a valve train so its timing (assuming a non-modded engine) can be changed only by the pipe chosen, the pulg, even the header to a degree and the fuel chosen.
With these factors in mind, you might be required to change all of these to make forced induction work on a nitro engine.

Jim air volume not pressure.... if 14.7 atmospheric is not enough to to properly charge the crankcase, you will not see any PSi by forcing more air in.... PSI is only generated when the moitor cannot consume the volume of air being forced into it.... therefore untill you throw more air at it you will not know if it will create boost or not...if the engine is filling the crankcase 100% under NA the of course you'll see boost, but if the engine is only filing to 50% capacity you will not register boost till the crancase reaches 100% capacity....boost is read from the intake tract.....

When we mod boosted engines we dont worry about PSI, it means nothing to us, we calculate air volume being pushed... if you have two motors each spinning the same blower at the same speed, and one engine is registering 14 psi and the other 7 PSI, it just shows one motor can pump air easier then the other..... I gues what I am trying to say is the crankcase doesn't need to be able to hold pressure, and you dont need to be able to produce PSI to make more HP...... Basically the SC is acting like a denser atmosphere pushing air into the engine... it is nothing more, as well the SC used for these applications are not positive displacement superchargers, they do not compress the air....

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Post #: 76

RE: were to find a turbo or supercharger kit - 10/18/2006 3:11:02 AM

125cchyperman

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Ok supertib so you think that I have no clue but for some reason you have yet to produce numbers on a engine to me or any other person on here. So once again your doing nothing but talking and not producing numbers. I realise that your getting frusterated at my question's. But I dont particularly care about you getting frusterated. But most of my questions you have yet to produce answers for me. You just keep on rating about how I have no clue and keep ranting on about atmospheric pressure being 14.7psi. But you keep telling us not to think of it as in psi yet you keep saying psi.

And I know that boost is not what creats the extra power. It's the extra oxygen that is in that air that creates that power. You could have 15(psi) of pure nitrogen or carbon and not gain a single hp.

But as I said above you have yet to answer any of my question and just keep on saying that I have no clue. But yet when it comes to supercharger's on nitro 2 strokes they dont seem to work now do they, I'm not here to start a flame war or anything like that as you have done so far(or atleast thats how I feel) against me. But thats fine my feeling remain intact and could care less. I have asked simple question about what I think you have done wrong and you have done nothing but come back and say that I have no clue.

But you have yet to answer my question so it makes it seem to me that you have no clue. About the only answer I have gotten so far saying that I was wrong along with something to back it up is downunder's post which I have some things that could be added but once again I will hear "you have no clue what you are talking about". Answer my questions as your the one who's stating that they do work so your the one who has to come up with the numbers and answer's not me. But once again I'm not here to start a flame war, but if your to mad at me to answer my questions then thats fine. But if you would answer my questions I could see where your coming from and we could get on the same page. I realise that you have a lot more years into this then I do and I have not questioned that at all, but yo havent furnished any answers to me at all beside supercharging is the same as higher air density's and the crank case pressure is 14.7psi. Thats about what I have gotten out of this so far and am left with a lot of question.

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Post #: 77

RE: were to find a turbo or supercharger kit - 10/20/2006 12:54:18 AM

SAVAGEJIM

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quote:

ORIGINAL: savagecommander

they use the escaping sound wave to push the mix back in... i dont see how more fuel in will upset the timing on the pipe???

Absuolutely. What is sound? Sound is pressure waves. As the sound wave moves from its source, the air volume will have areas of thin density and thick density. The desities are held in place by the pressure, but both the pressures and densities areas disperse as they travel until they reach equilibrium (i.e. silence). This is why an bomb eplosion far away is not as loud when you are near it.

Pipes use this same concept, and they say tuned pipe, they mean it literally since they tune the pipe for a give pressure resonance just like a piano tuner tunes the tension of a string by the same method (resonance). The tune of the pipe is such that you want the pressure node (wave node) to be at a specific point in the pipe to provide the the pressure in the appropriate place. This pressure node(s) stay at the same place but the intesity of the pressure is changed such that the amount of back pressure is altered for the given RPM.

This is one reason why a supercharger throwing more pressure and fuel/air volume into a nitro engine will cause performance problems. The the pressures are changed from what and where they are supposed to be for a given RPM. Will the changed back pressure amounts facilitate the use of forced induction such the back pressure is correct? This will require calculation. Since tuned pipes are finely tuned pieces of equipment and changing what goes into them will have a profound effect on engines turning at 1000RPM to nearly 40000RPM, assuming the increased fuel/air charge blowing into them at a given RPM will be sufficient to keep the increased density in the cylinder up is a serious leap . Engineering and calculations are required to find the right miz.

>>Edit: I realized my physics was wrong last night. Anyone else more versed in harmonics is very welcome to correct me where I am wrong; I am looking to learn and would prefer the ezperts to help me.

< Message edited by SAVAGEJIM -- 10/20/2006 12:44:09 PM >

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RE: were to find a turbo or supercharger kit - 10/20/2006 4:14:57 AM

125cchyperman

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quote:

ORIGINAL: SAVAGEJIM
If this node or the wave length is altered, the back pressure will not be correct for the given RPM.

This is one reason why a supercharger throwing more pressure and fuel/air volume into a nitro engine will cause performance problems. The wavelength and/or the presure node(s) are changed from what and where they are supposed to be for a given RPM.

Thats on the lines that I was thinking earlier, but wouldnt you think that the extra f/a mixture would also give the pressure waves problems from the stand point of there is more to push back and it will not be optimized.

At least this was along the way that I was thinking.

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RE: were to find a turbo or supercharger kit - 10/20/2006 1:43:47 PM

savagecommander

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The length of the pipe determines at what time the waves arrive back at the cylinder. Longer pipes require more time for the waves to traverse and so will be tuned to a lower rpm than a shorter pipe. The shorter the pipe the higher the rpm it is tuned to.

The rate of convergence/divergence of the cones determines the duration of the wave returned. A gentle taper give a long duration but weaker return wave while a steeper taper gives a short but strong return wave. The longer the wave, the broader the RPM range at which it is useful. This extra power band width is at the sacrifice of peak torque.

The diameter of the center or dwell section determines the ratio of scavenging suction to port blocking pressure as well as the over all energy recovery. The resulting volume determines the maximum pressure rise with large volumes giving less pressure rise. The fatter the pipe the harder it sucks but the weaker the blocking pressure. Thinner pipes will scavenge less but block the port very strongly. The optimum diameter is related to compression ratio, the quality of the transfer port layout and its scavenging efficiency.

but i still dont understand how more fuel will upset the tuning.....

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RE: were to find a turbo or supercharger kit - 10/20/2006 2:06:12 PM

supertib

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i give up with these engine experts lol...
okay everything balances out....more fuel in the crankcase =more fuel in the combustion chamber=bigger explosion in the cylinder=more pressure in the cylinder after combustion=stronger exhaust exhaust wave pulse..

all this means is when you add more a/f to the crank case it balances out in the end, the engine still will operate as normal..... and we are talking minute amounts of fuel in the exhaust headerm and even if we have more fuel the exhaust wave is stronger anyways from having a gbigger combustion...... a supercharger is not different then running at ultra low altitude period...the motor just balances out the pressures in the same way....

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Post #: 81

RE: were to find a turbo or supercharger kit - 10/20/2006 5:47:38 PM

125cchyperman

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well I knew just about everything you just said savagecommander but thanks for telling me anyways.

I never said that I was an enigne expert but the way your acting as if you are. But as I said above supertib you havent answered any of my questions and just always said that I didnt have a clue. But you never did give me an answer so it making me think that you dont really have a clue so thats why you didnt answer me. As I said before I dont want this to be a bash fest and dont want it to come to that. As bashing never get's us anywhere and just gets us in trouble with the mods.

But anyways I think we can put an end to this. This hole discussions started out about rb's supershargers and we can end with this. We all agree that rb's supercharger is not worth the money and does absolutely nothing in performance gains as any and all power that is gained is lost by the power that is needed to drive the supercharger and the extra weight that it add's makes it all that much more worthless.

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Post #: 82

RE: were to find a turbo or supercharger kit - 10/20/2006 6:44:53 PM

hpi apollo

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i'll chime in, i seem to recall someone like RC Driver doing a test on one of these things on a nova .21, and it made .1hp more and 1oz of torque more

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RE: were to find a turbo or supercharger kit - 10/21/2006 5:50:50 AM

SAVAGEJIM

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quote:

ORIGINAL: savagecommander

The length of the pipe determines at what time the waves arrive back at the cylinder. Longer pipes require more time for the waves to traverse and so will be tuned to a lower rpm than a shorter pipe. The shorter the pipe the higher the rpm it is tuned to.

The rate of convergence/divergence of the cones determines the duration of the wave returned. A gentle taper give a long duration but weaker return wave while a steeper taper gives a short but strong return wave. The longer the wave, the broader the RPM range at which it is useful. This extra power band width is at the sacrifice of peak torque.

The diameter of the center or dwell section determines the ratio of scavenging suction to port blocking pressure as well as the over all energy recovery. The resulting volume determines the maximum pressure rise with large volumes giving less pressure rise. The fatter the pipe the harder it sucks but the weaker the blocking pressure. Thinner pipes will scavenge less but block the port very strongly. The optimum diameter is related to compression ratio, the quality of the transfer port layout and its scavenging efficiency.

but i still dont understand how more fuel will upset the tuning.....

This is excellent information. Thanks for posting it. Based on these concepts, I will attempt to sketch a logitudinal diagram of a pipe to better understand what is happening. For a given gas flow going into the pipe, I hope to gain a better understanding of what kinds of back pressure will be provided (I was always curious how these pipes did this). I'm also going to see about purchasing a fluid dynamics book (look out Half Price Books! I'm coming your way!). If I can gain a more detailed understanding based on these concepts you mentioned, I hope I can eventually calculate a back pressure profile for a given pipe. I have a busted up one in my junk box somewhere, a hack saw will make short work of it.

Savagecommander, where ever did you find this info? I'd love to read up more on tuned pipes. If I can grasp the design aspects of tuned pipes, maybe I can come up with a design to provide the right back pressure to keep the supercharged fuel-air mixture in the cylinder to provide the additional bang that a supercharger is suposed to do.

RB Innovations? I guess it's junk. I do not know what its design is. Is it a roots type compressor? Is it a mechanically powered impeller? If it is a simple fan run by a silly rubber band, that is a far cry from what a mechanical compressor is supposed to be! RB Innovations deserves to have claims against them filed in the BBB. We can only hope to have an aftermarket company design and sell a supercharger that is based on proper mechanical compressor designs and is also reliable and actually provides a significant positive pressure boost.

Other variables to factor into the equations when determining if a supercharger will work on a nitro engine:
*What are the forces produced by the combustion of the fuel-air? Based on advertised torque at a given RPM, this probably can be calculated given the exhaust duration and the known bore and stroke of the engine. Problem here: advertised outputs are greatly pumped up and exagerated.
*What are the forces from the combustion actually entering the pipe? Given that we know the answer to above and given that we now the density of the burnt gases and what pressures they manifest, we can calculate this too. The RPM and therefore flow complicate this. This combinewith the other normal variables (ambient aire density, humidity, ambient temp, fuel used) exaserbate calculating this accurately.
*What is the engine combustion timing to make it optimal for forced induction to work (i.e. such that the correct back pressure is provided to keep the fuel-air mixture from shooting straight through the intake ports and out the exhaust port)? By asking this, I am refering to the plug and nitro% selection.

Given we know these variables and gievn we know the boost pressure of the fuel air charge, we would want all to work such that the back pressure from the pipe is slightly lower than the charge pressure such that the fuel/air charge fills the cylinder with as much fuel/air as possible. This back pressure must be great enough to prevent over scavenging of unburnt fuel/air.
Unfortunately, finding alot of this information is not possible: the engine and pipe makers do not relinquish this information. Reverse engineering is probably the only way to come up with more real world numbers, not just for the purposes of forced induction, but for actually calculating real world torque and power outputs.

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RE: were to find a turbo or supercharger kit - 10/21/2006 6:03:20 AM

smaxx3.3

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i have heard this topic on so many other message boards i have come to hate it

. it is impossibale to supercharge a r/c engine. even if you get boost you will just waste it cause when the intake port is open the exhuast port is open also so therefore just blowing fuel out the exhuast pipe. shorter run times, weight added to your car, at least you can say you have a supercharged r/c car

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RE: were to find a turbo or supercharger kit - 10/21/2006 6:32:56 AM

SAVAGEJIM

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quote:

ORIGINAL: smaxx3.3

i have heard this topic on so many other message boards i have come to hate it . it is impossibale to supercharge a r/c engine. even if you get boost you will just waste it cause when the intake port is open the exhuast port is open also so therefore just blowing fuel out the exhuast pipe. shorter run times, weight added to your car, at least you can say you have a supercharged r/c car

This is absolutely correct and what I came to realize this not even last week. Basicaly, most here in the thread agree here. For the tuned pipe to provide enough back pressure to keep a supercharged fuel/air mixture? I personally think the boosted charge will overpower the back pressure. As I just said, I want to learn more about tuned pipe design so I can actually provide more proof with numbers. I wish I also had a dynometer for nitro engines so I can conclusively do experiments for myself. Like HPI Apollo said, a magazine did an experiment and the engine made only one oz-in more torque! That is a far cry from the 5% to 15% advertised output increase (I cannot remember exatly what RB Innovations claims).

After reading these posts on multiple sites, I too become somewhat irritated how many actually believe the claims that RB Innovations advertises about its supercharger. I do not know if there are other nitro superchargers out there, but I strongly believe they too will not benefit nitro engines.

This is what I feel and believe; I am making assumptions, but I feel my assumptions are better grounded. If one makes the assumption that a tuned pipe will provide eneough back pressure to keep a supercharged fuel/air mixture from being overscavaged, I believe they are making a bigger leap.

Assumptions are just that, and this is why I am inspired to learn as much as possible so I can actually calculate the results myself. I need to master the principles and learn how to correctly express them mathematically; I also need to learn to fully understand all the other factors that affect nitro engine running in general (ambient temp, ambient pressure, humidity, how different plugs change timing, fuel blends, and so on). This is very daunting, but I am willing to learn. I want to be able to calculate real world numbers that conclusively say "Yes, forced induction works!" or "This is a load of BS!"

If there are any nitro engine designers who intimately know nitro engine specs and designs, please chime in. Feel free to speak to me in numbers, equations, and so forth; I am willing to learn all things technical about how nitro engines engineered.

< Message edited by SAVAGEJIM -- 10/21/2006 6:36:02 AM >

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RE: were to find a turbo or supercharger kit - 10/21/2006 6:45:20 AM

supertib

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guys any 2 stroke can be boosted no matter what size the motor is, the principles are exactly the same.... unfortunately there is no real superchargers to use on rc engines.... the boost does not just blow out the exhaust as you all seem to think... anyways there have been dozens of boosted 2 strokes that have been built and run.....and it doesn't matter if the engine is 500 cc or 4.6 cc it still plays by the same rules..... anyways a supercharger is just supplying more air easier to the motor....

and the rb unit is just a rubber band powered kazoo and just because it doesn't work dont assume 2 strokes cannot be boosted.

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