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  • Understanding Nitro Tuned Pipes / Exhausts

    Her er det litt info om tune pipes / exhausts ...

    Fant no dette, og tenkte det kunna verra greit med litt info om det , siden det er en del spm om dette . Er på engelsk , men di fleste forstår det .

    Understanding Nitro Pipes

    Header
    The header's length has a significant impact on performance. The rule of thumb is that a longer header is better for bottom-end power, while a shorter header makes your engine scream on the top end. The longer it is, and it resonates at a lower pitch. The shorter it is, and it resonates at a higher pitch. The idea is to adjust the length until the engine and exhaust system are in sync and “singing” in harmony. You can’t go too far in either direction, so don't be reckless; you'll do more harm than good. The ideal header would also expand outward (conical shape). This subtle expansion, when combined with those of the tuned pipe, helps scavenge, or suck, the exhaust from the engine. The header length is the number you play with when tuning your pipe. A heavier car demands a broader power curve, so a longer header is best. A light car, on the other hand, can be tuned for peak power on a narrow power curve with a shorter header.

    Divergent cone
    •A sharper angle of the divergent cone makes scavenging more efficient but limits it to a more narrow rpm range.
    •A more gradual divergent cone reduces the intensity of the negative wave, but it lasts much longer, so this increases the rpm range.

    It's a balancing act of sorts: more performance over a limited rpm range or less performance over a broader rpm range.

    Belly
    Parallel portion of the pipe, that connects the divergent to the convergent cone. It's length determines the relation between the negative and positive waves.
    •A short section is best for developing maximum power at high rpm ranges, but narrower power curve.
    •A longer section implies in a broader power curve with less peak horsepower. Its more suited for developing low-rpm power.

    Convergent cone
    •A sharper angle of the convergent cone limits engine to a more narrow rpm range.
    •A more gradual convergent cone increases the rpm range.

    Stinger

    The convergent cone ends at the stinger ( the pipe portion opened to atmosphere ) which expels the burned gases way out. It works as a pressure bleed valve and controls back-pressure, enhancing the port plugging efforts. If it is too small or too long, you may have engine overheating problems. Too small a stinger causes excessive back pressure into the pipe and raises the pipe and engine temperature.
    The ideal stinger diameter should be .58 to .62 times the header diameter, and its length should be 2.86 to 3 times its own diameter.

    Stinger diameter affects the top and bottom end.

    •Bigger = top end at the sacrifice of low end torque.
    •Smaller= low end at the sacrifice of high end revs.
    Stinger length affects the top and bottom end.
    •Shorter = top end at the sacrifice of low end torque.
    •Longer = low end at the sacrifice of high end revs.

    The stinger's ideal diameter and length are important to performance, but are limited and governed by most racing sanctioning bodies.

    Tuned Pipes Design Examples

    Small volume - narrow operating range (peaky)
    High volume - lower power (if too big) - broad range
    Steep angles - 'peaky' - high power
    Shallow angles - broad range - moderate power
    Shorter or larger diameter stinger - lower or higher pressures and heat.

    How to Pick a Tuned Pipe•Torque biased.
    Sharp cone on each end long flat band center, single chamber.

    •Low-mid biased. Aggressive divergent cone.
    •Mid biased. Moderate divergent cone.
    •Mid top end biased. Moderate divergent cone aggressive convergent cone.
    •If the engine is a short rod rever you need a torquier pipe to enhance the bottom end as engine will be biased and take over on the top.
    •If the engine is a long rod engine you need a rev pipe to help the engine unload on the top.

    Pipe length

    The way you intend to use your car in combination with your engine, will dictate the optimal length for the pipe.
    The shorter the pipe, the higher the peak horsepower and torque, but the range of the horsepower and torque gets narrower and drops off faster. Also, the shorter the pipe the more fussy your engine will be.
    •Shorter=top end at the sacrifice of low end torque.
    •Longer=low end at the sacrifice of high end revs.

    For optimum performance, the following guide may prove useful.

    A) Overheating / Hot Weather
    •Increase combustion chamber volume or head clearance.
    •Increase stinger diameter or decrease stinger length (to reduce pipe pressure).
    •Decrease nitro content of the fuel.

    B) Cool Running / Cold Weather
    •Decrease combustion chamber volume or head clearance.
    •Decrease stinger diameter or increase stinger length.
    •Increase nitro content of the fuel (if the competition rules allow).

    C) Pipe Length Too Short
    •Frequent blowing of glow plugs
    •Sand blasted head
    •Over heating engine
    •Difficult to get 'on the pipe', sensitive needle
    •Excessive carbonizing of the head
    •Engine sags under load
    •'Harsh' running

    D) Pipe Length Too Long
    •Very easy on the needles
    •Smooth, quiet running
    •Prone to burbling, rich running
    •No power
    •None of above, try shorter and see what happens.
    Lars Erling Olsen 1981 Trondheim Losi 22-4 - Losi 22 2.0 - 2x Xray T4 16 - Sanwa M12



  • #2
    Fortsettelse

    Unlike four stroke engines, in which intake and exhaust valves retain fuel in the combustion chamber, a two stroke engine depends on the header and tuned pipe to retain fuel in the combustion chamber.
    It has been said that the single most performance gain that one can achieve on a two stroke is made by strapping on a tuned pipe. This is very true if it is done properly. Don't just go down to your hobby shop and purchase a pipe marked ".12 Tuned Pipe" or ".21 Tuned Pipe".

    How it Works:

    Starting with the moment the engine fires, forcing the piston down and the exhaust port begins to open the exhaust gases are forced out of the engine and start to travel down the 'header' section of the pipe. Before long the gas reaches the expanding / divergent / cone. The effect is a pressure drop, creating a vacuum which helps 'pull' the remaining exhaust gases out of the engine.

    Not only are the exhaust gases being 'sucked' out of the engine, the fresh intake mixture is being 'drawn' into the combustion chamber from the crankcase via the transfer port. Some of this new charge will follow the exhaust gas straight through the still open exhaust port.
    The exhaust gas travels down the pipe, through the expanding cone till it meets the reflecting / converging cone. The converging cone forces the pressure to rise, generating a pressure wave which reflects back towards the exhaust port.
    As the reflected wave approaches the exhaust port, it forces the fresh mixture (which flowed through the combustion chamber), back into the combustion chamber. As the transfer port closes before the exhaust port, this results in a pressurized charge in the combustion chamber as the exhaust port closes. The result - super-charging your engine - more power.


    Sections of a Tuned Pipe

    Header -

    Although not part of the tuned pipe, the header plays an important role in the overall tuning of your engine. The header attaches to the engine and is the straight or slightly divergent (opens up 2-3 degrees) section of the pipe. It helps to suck the exhaust gases out of the engine. The header pipe cross-sectional area should be 10-15% greater than the exhaust port window for maximum output at maximum RPM's is desired. In some cases the area of the header pipe may have a cross-sectional area 150% of the exhaust port area. The length should be 6-8 times its diameters for maximum horsepower. For a broader power curve, 11 times pipe diameter may be used. This is the part in which you trim length to tune the header.

    Divergent (Diffuser) Cone -

    The section of the pipe that attaches to the header and opens up at an angle like a megaphone. It intensifies and lengthens the returning sound waves, thus broadening the power curve. The steeper the angle the more intense the negative wave returns, but also the shorter the duration. The lesser the angle, of course, returns a less intense wave, but for a longer period of time (duration). The outlet area should be 6.25 times the inlet area. It usually has 7-10 degree taper angle.

    Belly -

    Located between the divergent and convergent cones, it's length determines the relative timing of the negative and positive waves. The shorter the belly the shorter the distance positive waves travel and the narrower the RPM range. This is good for operating at HIGH RPM only. The longer the belly the broader the RPM range. The diameter of the belly has little or no effect.

    Convergent (Baffle) Cone -

    Located after the belly and before the stinger, reflects the positive waves back to the open exhaust port and forces the fresh fuel mixture back into the combustion chamber as the exhaust port closes. The steeper the angle the more intense the positive wave and the gentler the angle the less intense. It usually has 14-20 degree taper angle. The taper angle primarily influences the shape of the power curve past the point at which maximum power is obtained.

    Stinger -

    Located at the opposite end of the pipe from the header and after the convergent cone, it is the "pressure relief valve" of the pipe where the exhaust gasses eventually leave the pipe. The back pressure in the pipe is caused by the size (diameter) or length of the stinger. A smaller stinger causes more back pressure and thus a denser medium for the sound waves to travel in. Sound waves love denser mediums and thus travel better. A draw back to a small stinger is heat build up in the pipe and engine. DO NOT USE TOO SMALL A STINGER! The stinger diameter should be .58-.62 times that of the header pipe and a length equal to 12 of it's own diameters.


    Selecting a Tuned Pipe

    What do we want?
    1) Quick acceleration
    2) Broad RPM range
    3) Broad to lower power range
    This means we are probably not going to turn the maximum RPM's that the engine is capable of anywhere on the course. If our engine is capable of turning 40,000 RPM's, we will probably only use up to 35,000 RPM's. Look at each section of the pipe in the above descriptions. The Header cross-sectional area should be at least 10-15% greater than the area of the exhaust port. Length at this point doesn't really matter (at least 8 diameters), but make sure it is long enough to work with. The divergent cone would be at a medium angle for a broad power curve at lower RPM's. The belly would be medium to long for a broad RPM range. The convergent cone would be at a gentle angle because we want the duration of the positive wave to be longer.

    How long is the pipe? The formula for determining the length is:

    Lt = (Eo x Vs) / N English OR (83.3(Eo x Vs)) / N Metric
    Where:
    Lt = tuned pipe length, in inches or millimeters
    Eo = exhaust open period, in degrees
    Vs = wave speed (1700 ft/sec or 518.16 Meters/sec at sea level)
    N = crankshaft speed, in RPM
    Let's say, for example, we have an engine that will turn 25,000 RPM. We calculate that we will only use 20,000 of those RPM's and our exhaust duration is 180 degrees. Then we substitute in the formula:
    Lt = (180 x 1700) / 20,000 OR (83.3(180 x518.16))/ 20000
    Lt = 15.3 inches OR 388.46 mm
    Now this is where you need to make a personal decision. Some people say that this distance is measured from the exhaust port opening and some say that the distance is from the center of the cylinder. The choice is yours, but I take the longer distance, which is from the exhaust port opening. Remember that this is not the total length of the pipe. This is the length from the (in my choice) face of the piston at the exhaust port to the center of the convergent cone including the invisible intersection of the convergent points not just what you see.

    Tuning the Pipe

    Now comes the fun part! We get to go to the track, unless of course we have our very own dyno.
    So we have set the pipe up so that we have an optimum length. First we want to get the right gear ratio, right fuel and right needle before we even mess with that pipe. You see this is where the "What a pipe can't do?" comes in. A pipe cannot make up for poor engine setups and crappy gear ratios. A pipe also cannot make up for bad engine timing and some engines are timed so poorly that no pipe will increase performance.
    Ok, we make a few (2-3) passes. We pay close attention to what the engine is doing.
    If We have the right gear ratio, and the right needle setting and the engine runs slow, something is wrong. If the mixture is correct then pipe is too long. Shorten it by 1/8" at a time until the revs start to rise (this can be done at the exhaust coupler).
    If the pipe is too short the motor will run harshly and the needle setting will be unstable and critical. Add 1/8" to the length at a time (again, at the coupler).

    When the pipe is at the proper length you will experience the thrill of a lifetime. You will hear the engine and pipe become one in resonance. You will see your car accelerate like you walked behind it and gave it a kick in the rear. This as known as being "on the pipe".

    The good thing about today's in-line pipes is that they come almost tuned for best optimal average performance for the engines they are designed, and most offer you three different optional headers for fine tuning (short, mid and long). There is no bad pipe, just a bad choice for the application you intend for it.
    Lars Erling Olsen 1981 Trondheim Losi 22-4 - Losi 22 2.0 - 2x Xray T4 16 - Sanwa M12


    Comment


    • #3
      Finnes jo potter på markedet som har eksosventil.....

      Har en slik selv jeg:

      http://cgi.ebay.com/Alu-Tuned-Dual-E...QQcmdZViewItem
      RS4 Evo+ Savage 4.6HO Savage XSS 5.9
      HiTec 40MHz

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