PIT TALK (Bulletin 7) Variable Tunepipe control
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I have been working on this idea for some time now and have now got the system working very well. The exhaust control was fitted to my 3.5 and 7.5 that went to the12th World Championships in Velenje. As many saw, it works very well and gets that boat moving when used. This system has plenty of potential and will change the speed of many boats in future.
NOTE: I have no problem that people copy this idea as I have indicated at the World Championships and have allowed many people to take photos of my boat. Below I will also give you some detailed information on how to do so. Well let me tell you that if you do not copy it you will be left behind very shortly. That is a Guarantee!!
How does it work?
It is a very simple idea of just shortening the tune pipe by means of a servo as and when you require it.(Well that is if you do not get too fancy). Yes, there are many ways that this idea can be used to improve your speed and performance round corners that we will discuss later.
What does it consist of?
|Variable tunepipe control mechanism.
Silicon O-ring seal
Radio that can do mixing of channels (Recommended) and can handle another servo in your boat.
How should it be set up?
Look at the pictures with explinations of some details of my design for all to see..
The exhaust system is setup to be able to move the pipe by about 1 cm. Yes, this sounds like a lot but actually can be just fine when in a race. The long pipe will be your usual length that you used to race with before you made your Variable pipe control. The short pipe is then that pipe that will get you going down that straight when you want it. You have the option to mix your rudder with it or your trim tab with it if you want but what is more important is to mix it with your mixture control. It must be noted that when you shorten your pipe you need to make your motor richer. If not you will run your motor lean. This will end up as a stationary boat on the water which helps you absolutely nothing. So I advise you to only start mixing with other channels once you have your mixture control mixing sorted out.
I run mine manually and only use it when I need to. You also need to keep in mind that your motor will rev its head off if not controlled. I have found that there is no limits to how short you go once you on the plain down the straight. You could even make it 2 cm`s shorter and your boat will just go faster. Does this not sound incredible? Well it is true. I run in the region of 2000 RPM more down the straight when I shorten the pipe. This can however vary depending on how short you make it. I repeat that your engine is more your limiting factor at this time of the game. To give you an idea. My direct drive 7.5cc FSRV was tested at the test lake at Velenje with MR PICCO. Once I put the pipe shorter I peaked just short of 75 km/hr. That was with no detailed tuning and optimization yet. For example I could still turn corners without coming off the pipe. Thus I had to actually make the pipe shorter. I had other problems however being that the Vortex could not handle that speed anymore. It would serve no purpose making the pipe shorter and going even faster. I will have to get the Spider and then I think I should be able to use that speed.
This was the first time I ran the system at see level (close too) as this system was designed to work at 6000 feet above see level. I found coming down to see level that I just had too much power for the boat. Hard to believe but you can find out for yourself and then you will believe me.
Happy boating and hope you all get those boats really going. I am sure many people are going to have to build new boats in future to handle the additional speeds we will be seeing. Like I said before 100km/hr for V is not far away at all. I think the 120 km/hr is rather the challenge.
Compiled by Gary Baldwin
Last Updated on 03 Apr 2001
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