Tuning the exhaust pipe on your model gas boat

Let’s face it, by virtue of human nature we are all looking to build the fastest boat at our local pond.
While you will probably find the most beneficial speed gains through setting up your hull properly.
The majority of us start by throwing different props, pipes and petrol at our boats.

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Before we start, it’s worth pointing out that there really aren’t any bad tuned pipes on the market. Most will function well in the right hands. What you will find however that they will all respond to tuning differently.
Some can be quite easy to find the ‘sweet spot’ and others can be more suited to someone with the patience to try lots of different lengths and prop combinations.

Thankfully there is with a wide variety of tuned pipes on the market. Ranging from the very popular Quickdraw tuned pipes made in America through to the ultra-expensive JB Pipes made in the Netherlands.

Things to remember before buying your pipe:

  • Buying the most expensive pipe on the market won’t make you the fastest guy at the lake.
  • 1″inch inner diameter doesn’t mean it’s faster than a 7/8″ system.
  • An internal stinger will often reduce enough noise to not require a bulky external muffler.
  • You should re-tune your pipe and carburetor needles when making major changes to the type of prop you are running on your boat.

What tuned pipe system do we recommend?

To be honest we don’t recommend any particular exhaust system. Personally Aaron runs the Zipp Kits tuned pipes on the majority of his boats and Daniel runs the Quickdraw tuned pipes on the majority of his.

If we were to recommend one based on price, performance and portability – it would probably be the Zipp Kits Tuned Pipe V3. Coming in at around AU$130 for a complete system, it’s not only cheap but well built.

The pipe itself is built from stainless steel and includes an internal stinger so you do not need to run a bulky external muffler. The combo can come in a range of different configurations with options including a 90, 100 or 105 degree headers. The 90 degree headers also have the option of 1″,1.5″, 2″ or even 3″ offset from the exhaust port. Finally you can also pay an extra $1 and have Zipp Kits pre-cut the header so it’s a quick and neat installation.

Take note: This system is best suited for any Zenoah G230, G260, G290, G300 and equivalent RCMK and Tiger King. For a G320 or above, it’s probably better to start looking at a system with a 1″ inner diameter header.

How do I tune the Zipp Kits Super Tuned V3 pipe?

The Zipp Kits pipe was designed to provide a long, flat torque curve so that you can pull a wide variety of props while staying in the usable RPM range. This pipe will keep up with all of the fancy and expensive pipes, as long as you understand what you are doing.

There are many good web pages that describe exactly how tuned pipes work, but the only thing you have to know is that they use sound waves to force the fuel/air mixture back into the cylinder before the piston closes the port. If the pipe is too long or too short, the cylinder will not fully charge and you won’t see a big gain in power.

Set the pipe at exactly 13.5 inches from the face of the exhaust port to the largest part of the tuned pipe. Be sure to measure along the centreline of the header, around the bend. With the pipe at 13.5, try different props until you find one that the boat likes.

Now that you have a baseline. Run the boat and try to determine when the pipe “hits”. If you pay attention, you can see and hear when the pipe hits.
It is like a little shot of nitrous.

With the boat on plane, very slowly open the throttle. You will find a point that the engine seems to just jump in power. Do this several times and try to remember where the throttle is when this happens.

If the pipe is too long, this will happen below half throttle.
If short, you will never feel it at all.

In a situation where you think it never ‘hits’ pull it out ¼ inch and try again.

For oval racing we want the pipe to hit at around 70-80% throttle.