Friday, September 30, 2011

Tuned Pipes - Part 2

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First a quick review of tuned pipe theory. The pipe produces two pressure waves at the exhaust port. The first, a low-pressure wave, is created by the diffuser section of the pipe when the exhaust port opens. It reaches its lowest pressure when the piston is at bottom dead center and helps draw fuel up through the transfers. The second wave is a high-pressure pulse created by the baffle cone that arrives just before the exhaust port closes and supercharges the cylinder. The picture below shows the timing of the pulses created by a multi cone diffuser and the baffle cone relative to the port open time. The baffle cone produces Positive Sonic Wave 1 and each section of the diffuser produces Negative Sonic Waves 1 through 3.

web-Multi-cone-Pipe-Pulse-G
There are several types of diffuser in use. The simplest is a single cone that tapers up from the header diameter to the maximum pipe diameter. This has evolved into multi cone diffusers that look like a roughly shaped horn. These two styles are shown in the picture below. The top two pipes have multi cone diffusers on the left side of the maximum diameter section, while the bottom pipe has a straight cone diffuser. The top pipe’s diffuser has a higher horn coefficient than the second pipe. That is, it expands more suddenly then the diffuser section of the second pipe. All these pipes have the same maximum diameter, the same baffle cone and the same tuned length.

web-20k-pipes
The tuned length of these pipes was designed to produce best power around 22,000 to 24,000 rpm, with the top pipe producing the lowest power and the bottom pipe producing the highest. The top pipe should have the broadest power band while the bottom pipe should have the narrowest. Below are the actual test results on a modified CMB 35.  Nearly all the lines represent the average of two or more runs. Where there is scatter from a single run, an average line is drawn through the points.

The problem with the actual pipes on a real engine is that they produce two power peaks and the second peak is probably higher than 24,000 rpm. All the pipes turned out to be too short. This happened because I used the wrong average temperature in the pipe design program. The power band on the pipe with the straight cone diffuser is so narrow and the trough is so deep that the engine won’t rev much beyond the first peak. The pipe with the 1.2 horn coefficient diffuser looks like it has a narrower power band at the high rpm peak, but it’s hard to tell since the peak wasn’t reached. The pipe with the 1.4 horn coefficient might work as a high rpm pipe. It is interesting to see how water injection into the header of the 1.4 horn coefficient pipe affects the power. This cools the exhaust and is the same as making the pipe longer. 

Two more pipes were made to a longer tuned length with the same diffuser section. The first was lengthened by lengthening the maximum diameter band section, and the second was lengthened by lengthening the baffle cone. The length to the stinger was kept the same on both pipes. A comparison of these pipes is shown on the graph below.

Figure 1 — Test results on a modified CMB 35 Figure 2 — Longer tuned length with the same diffuser sec-
Figure 3 — Wide band version of the longer pipes Figure 4 — RPM versus time

As you can see, there is very little difference even though the tests were run with both .600 and .625 diameter stingers.  The dark blue line is a test on the shorter pipe tested before but with a larger stinger.  It has lower power than the longer pipes except above 23,000 rpm.  We have also reduced the trough in the power curve by adjusting the carburetor fuel delivery with the high and low range needles. Further testing on the wide band version of the longer pipes is shown below.

Again it is interesting to see that an inverted stinger doesn’t significantly reduce power and that water injection really helps at lower rpm. Actual testing of the long cone pipe in a boat produced equally interesting results. One graph of rpm versus time is shown below.
The first plateau is reached at 20,000 rpm with the water injection on. Turning the water injection off allows the engine to rev to 23,000 rpm. These rpm readings agree well with the points where the long cone pipe begins to lose power. The space between each vertical line represents one second and the boat is going around 50 mph at 12,000 rpm in this test. It takes much less than ½ second to accelerate to over 80 mph with the water injection on. The rpm remains flat indicating that the boat is not gaining speed after reaching 23,000 rpm. In this case the pipe is governing the maximum rpm and the prop pitch limits the maximum speed. If the second plateau had been sloping up the boat would be still accelerating.  It took around four seconds to travel the length of our test pond. 

Tuned pipe development can be done with much simpler tools than we used. Data loggers and dynos just make it easier to see things. Given correct inputs, there are several good computer programs that will produce good pipes. Simple speed tests can separate the good from the bad pipes. Remember, props are an important part of the combination. In the example above, the prop didn’t have enough pitch to use all the available power.  Engine port timing also interacts with pipe design. A 35cc engine with 150 degree exhaust duration will never rev to 24,000 rpm, no matter what pipe is used.


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Thursday, September 29, 2011

Tuning Tools

11 March 2010 Reader Submitted Misc Article... by Carlo Catalanotto

Some good tips on tools that can be very useful for tuning your boats...
GPS, Radar Gun, Stopwatch, Tachometer
I have seen debates about all of these items and which is the best way to tune your boat on all the popular forums and the truth is that none of them are the one perfect gadget. All of the items mentioned in the title can be valuable tools when used correctly, but you must remember that these are only tools that give you information and if you don’t know what to do with the information then these are all useless. None of these are going to make your boat any faster by themselves, but knowing what to do with the info they give you is the real secret to setting up a fast boat. I am fortunate enough to have and use all of these to set up boats and will give you my opinion on each of them.
GPS
If you just want to know the top speed of your boat then the GPS is perfect for doing that. It is accurate simple to use and you can do the testing without assistance from anyone else as you simply place it in your boat and go run. They are inexpensive and will at least let you know the speeds you are seeing. It is one of my favorite tools and if you use it correctly and watch what your boat is doing around the course and through the corners it can help choose a prop or a setup that will work well on your boat. If you are making a simple pipe adjustment or changing to a prop with a little more pitch then just a few laps and you have an answer.  I think the GPS works great and have helped me get many boats dialed in and up to speed.
My experience with the GPS units is that if you are going to use one then use the big yellow E-Trex unit as it always seems to be dead on compared to the little green Gecko ones that I have personally seen give false numbers on more then one occasion. If you are using it to help tune your heat race boat then make sure to drive at a slow speed to you are on the course before letting it rip as to not give you any readings that could be from a long run up.
Radar Gun
The radar gun is also useful if you want to use it to get corner speed or Straight away speeds as a reference for your boat. I am of the belief that if you are going to use one correctly that it will need to be mounted on a tripod to be at all accurate for comparison type of testing. In all of the testing that I have done I have found it to be less accurate then the GPS when standing on the shoreline holding it in your hand. Unless you are standing directly in front or behind the boat while testing the readings will vary from any angle that the radar gun is submitted to. How many times have you seen a guy following the boat as it goes by with the radar gun? They are designed for reading a straight line coming directly at or away from the gun and any angles or movement will affect the reading. I still think this a good tool and used correctly can help you make tuning decisions that can help make your boat faster.
My experience with the radar gun is that there is way too much movement and angles for any kind of comparison testing unless it is mounted stationary for your testing. Mount it on a tripod have someone take notes each time you make a lap of the speeds being recorded and make changes accordingly to increase the speed and it is a great tool.
Stopwatch/Timed Course
The next thing that is becoming the most talked about testing tool is the stopwatch. It is also my least favorite among the list. I am a firm believer in lap times and consider this the best way to truly know how fast a boat is around the course. When used correctly a timed course will let you know what lanes on the course are the fastest for your style boat. It will let you know what prop is getting you around the course the fastest no matter what the top MPH is and it will let you know what adjustments are making your boat faster around the course.
My experience with a stopwatch is that the human element of the testing is way too inconsistent. To think that a person controlling the stopwatch is going to be accurate within a few tenths of a second each lap is unrealistic as it can vary as much as three tenths of a second or more. Excitement, adrenaline and nerves among other things when testing a new part or setup can easily effect how fast or slow the triggerman is on the stopwatch. Then there is the driver factor that you have to add to the equation. If a driver is trying to compare props or setups and makes a lap in lane 1-1/2 instead of lane 1 or over shoots a corner just a little and has to drive back to correct then all of this will make a huge difference in lap times. If the information from the lap times has varied because of one or more of these reasons combined and you are using this information to tune and adjust your boat then you can easily make poor choices. In my opinion there are just way too many variables when using a stopwatch by hand and it is because of these potential inconsistencies that the handheld stopwatch is my least favorite way of testing. . If you have access to a timed course to tune your boat with some sort of transponder system or timing lights then this is one of the best ways to tune your boat.

Tachometer
A tachometer is a great tool to monitor what your engine is doing while going around the course. It can also help you make slight tuning adjustments (Pipe, Carb) and see if the changes you have made are in the right direction. It is also one of those items that by itself is not going to give you a lot of information, but combined with a GPS or one of the other items mentioned can give you information about what your prop or set up is doing in relation to the engine.
My experience with the tachometer in a boat is that when used correctly it can be a great tool for tuning your engine and helping to choose the right prop or setup. Once you have your boat dialed in and have a baseline it is great for monitoring the health of your engine after each run and possibly letting you know something is wrong before major engine damage occurs.
Conclusion
The best advice I can give with all of these tools would be to use the ones that you are comfortable with to help you get your boat dialed in. There is not one magic tool that is going to turn your boat into a screamer all by itself. The more information you can obtain from the any of these items the better off you will be.
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I agree with those two pieces (speed and revs)there is no human error to comprimise the end result.
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Saturday, September 10, 2011

RC Car Racing – How To Get Started – Tips & Tricks At The Track!

Probably the most vital part of being a dedicated RC enthusiast is taking the hobby to the next level and getting out to the race track. If you don’t have a clue where to start, there are tons of organizations that cater to the RC cars hobbyist and make available listings of local or regional clubs – as well as some national ones.

So if you’re looking for a track to do some rc car racing in your neighborhood there are several online directories you can use, but the one with the most comprehensive information is offered here at RC Universe

HOW TO GET STARTED IN RC CAR RACING


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Friday, September 9, 2011

Tips On How To Tune Your Nitro RC Car Engine

So you want to know how to tune your nitro RC car engine, but you don’t really know where to start. Not to worry I got you covered.

The first thing you should know about nitro engine tuning is that it’s very important for the life of your motor and total power output. This page will serve as a basic but informative way on how to tune your nitro engine for supreme power. Ok so let’s get started!

You can also check out other how to rc articles – rc car reviews or see our rc car article directory.

Check it out…

How To Tune Nitro RC Car Engine


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