Modelgasboats.com - RC Model Boat Magazine

4-Stroke Power

Friday, 01 December 2006

Tech Article ...by Len Williams

Four-Stroke power for model boats??? Read this to learm more about this interesting concept!

Four Strokes in RC Gas Boating?

In this multi part series devoted to the theory of thumpers in an RC boat, we'll go hand in hand through a process of finding out, just what the possibilities might be.

The idea seems natural, that economical, environmentally friendly, good for the air, good for the ears four strokes would be a possible fit in our hobby. There have been some recent product releases that are leading the way in miniature four-stroke development and technology advances.

In our series we will be working with one that shows some promise and fits our criteria quite well.

Looking at what is available on the market and having some predetermined requirements, the Honda GX series was chosen for this project for several reasons.

The Honda differs in that the engine contains the oil and all you add is gas. Some models out there still require a pre-mix which defeats a portion of the "environmentally friendly" requirement.

Some things come to mind when we think of a 4Stroke, we think of :

Power and weight
RPM Operating range
Durability
Dependability
Water in the oil!!!
Modification possibilities
Feasibility in racing

These are a few of our initial concerns and feel free to write the editors with any thoughts you may have. This series will be interactive in that we will look at the reader mail and do our best to incorporate those comments and questions throughout the adventure! And this is an adventure! We welcome your participation.

Here are some comments that have been picked up along the way that you will find of interest and possibly agreement:

"It will never work"
"Too heavy, not enough power"
"Water in the oil, instant death"
"Too expensive to make modifications, cams are tricky"
"Will never be fast enough"

Some of what was said is exactly correct and warranted but not inherent flaws, only opportunities.

"Those who say it can't be done should make way for those who are doing it"

So, there's the groundwork, we have an idea, we have the pieces and now the journey.

Project: Four-Stroke Prop Twister
Subject: The Honda GX31
Primary Objective: Stuff it in a RC boat
Secondary Objective: Make it go fast and live!

There is a small group of people who have been working on this project for quite some time. Development has went a great distance and is ongoing almost daily by a few dedicated and talented individuals who have the tools and technological skills to correctly adapt to new thinking and thorough process of development.

We're not going to let the cat out of the bag right off from the start, but let me say, it is working.

Let's look at the Honda GX31. It displaces 31cc of course, is an overhead valve design, has a pressurized oil mist circulation oiling system, which has an oil tank complete with dipstick! The engine is well engineered and built with strong parts and a strong design. You can find all the technical information and specifications here (Honda power link).

Power is rated at 1.5 hp with a max operating rpm range of 10,000 (It will rev higher). The RPM range is the first thing to come into question, it's kind of low when we compare to our Zenoah mainstay which is capable of 17,000 plus in maxed out race motors, but generally operate in the 12,000-15,000 range.

Weight

This is no lightweight but it's not a tank as it appears from pictures. We are still working on putting this thing on a diet so no true bottom line weight has been established as of yet, but significant weight can be saved...more about that later. Even in full dress as it comes out of the box with it stock peripherals, weight doesn't seem to be a problem. Another thought may be the higher center of balance from all the goodies up high on the head, but again, it doesn't seem to be an issue. It has most of its weight down low.

Here is a comparison to a Zenoah PUM motor. It appears to be quite large, but most of the bulk is shrouding and stylistic parts. It is not much larger than a full dress Homelite 30cc. It has a wider footprint than anything else that's been put in a boat due to the oil tank.

Keeping the water out!

This is a major concern, and how to deal with it efficiently and effortlessly. There is only one way for water into the oil and that is through a breather tube that attaches to the air box. Some creativity is required in this area and some developments are ongoing. Contrary to what some may believe, it does not mean instant death if you have to dump out milky oil once in a while. Running it when you KNOW there is water in the oil will kill it. It's going to happen but the goal is to minimize the possibilities.

Dependability and durability?

Those two requirements are exactly why the Honda was chosen. When looking at the available candidates, there is no shortage of respect of the capabilities of a Honda product.

Modifications, and is it fast enough for competition?

The answer is~ we think so. When approaching this project it was my first concern because I race. It's the meat of the hobby for me personally.

There's not a whole lot that has been determined an absolute success in the modifications so far, but almost all the parts have been modified in some way up to this point, yes, even cams and the answer is~

More to come in the next installment of FourStrokePower!

Read Part 2!