Custom 7.7cc DOHC 4-stroke single cylinder engine.
Briefly, this project is a single cylinder glow engine to power my 1/8 scale desert buggy
. The target performance is over 25,000 RPM, 1.5HP. This is by far the most challenging project I have undertaken and is one of the things I have been building up to over the time I have been doing model engineering - about 10 years.
For years now I have been wanting to develop my own 4-stroke engine for car use. There are a number of reasons, not least because I believe they will become much more common in the future. They are much cheaper to run and can be a lot quieter which have major advantages nowadays. More importantly to me, they are more suited to forced induction and multi-cylinder configurations, and have a greater scale appeal with superior sound and appearance.
What I really want to do is build a 'modern' multi-cylinder engine for use in a large RC car - something like a 1/5 scale vehicle. By modern, I mean not an American style V8 from the 1950s. Now I don't want to take anything away from the guys who model these engines, there are some incredible craftsmen out there doing just that. These are the very people I have learnt a massive amount from. They model the engines they loved when they were younger, I wish to do the same. Where they had large displacement, hemi heads, crossplane cranks and pushrods, the engines that spark my enthusiasm have more electronic control, turbos, variable valve timing and high rev capability. Why not try to bring some more modern technology to the RC car scene? After all, a car engine right now is not much different from a common 2-stroke aero engine. The requirements from the engine could not be more different, yet the engines are really very similar. My opinion is that this is for a combination of two main reasons - durability, which is good with the current simple designs, and lack of real development in radical new directions.
Electric will get you!
Nowadays the electric equivalent of any RC car will almost certainly outperform the nitro powered version. They are faster, accelerate harder, require less maintenance, the list goes on. Many nitro fans cite the fact that without the smell and noise electric will never appeal to them. Well I can see that, but the shrill buzz of a 40,000 RPM two stroke isn't the nicest sound to the ears. This is the time when nitro engines need to move their game up, go to 4-stroke and up the cylinder count. Might I suggest a move to far cheaper petrol fuel rather than glow fuel would be a huge step forward too.
IC will NEVER be able to suppass electric from now on. The power density of the modern brushless motor will not allow it. The advantage lies in the failure mode; generally a motor will fail from heat soak - get the windings or the magnets too hot and it is game over. Critically this takes time, and in a car the maximum power is only ever needed for a very short burst, which the motor can easily handle. Now with an engine, you must size the powerplant to cater for the burst load requirement, not the average load. If you try to take 50% more than the design output from a nitro engine it will fail every time. So the whole system becomes larger, heavier and slower to respond.