I had always recognised the four letters stamped on the side of the engine of my 1991 XR250R – RFVC. At the same time though I had never known what they stood for, but often wondered. How many people can answer that question… not many I guess.
RFVC stands for Radial Four Valve Chamber. The four valves are tilted towards the center of the piston which creates more room and allows them to be bigger then if they weren’t.
What Is An RFVC engine?
As stated above an RFVC engine has 4 valves. In any 4 stroke engine you need a minimum of 2 valves. One valve to allow air intake and the other for the exhaust.
Having 4 valves means you will have 2 intake valves and 2 exhaust valves which for the engine means greater air intake when compared to a 2 valve engine. (A 2 valve engine would obviously only have 1 of each valve but both would be bigger)
This is explained very well in the video below.
So greater air intake and exhuast intake makes for a more efficient and powerful engine. This is because the more air that can enter the chamber, the more power is made when it combusts. Equally having 2 valves to release the burnt gases means it loses less power when getting rid of them so the engine is more efficient.
With This In Mind, What Is Different About The RFVC Compared To Other 4 Valve Engines?
This is what I thought straight away when I was researching this. The answer seems to lie with the ‘Radial’ part of what RFVC stands for.
The only thing I could find on this is that by having a radial presentation (think 4 valves positioned so the tops are in a dome shape ), that it allows room for the valves to be bigger which in turn means you can create more power.
It’s worth saying that this radial shape was not invented by Honda, it is known as an hemispherical engine and had been in use since the 30’s in Europe. The alternative to this is a Pentroof design.
The pentroof is best described as a tent shape, with 2 plains. You would have 2 inlets on each plain and usually both air inlet valves together on one plain and both exhaust valves on the other.
As Honda didnt design the Hemispherical way of doing things they have effectivley just created a way of markerting theirs by coming up with a new name, taking the acronym from it (RFVC) and stamping it onto the engine.
To be fair I have always known RFVC have been to do with Honda long before I knew anything about engines. (Which still isn’t a lot….although Im’m learning).
4 Stroke Engine Animation
If like me you are somewhat of an engine novice then you may find this next video interesting, which is why I have included it. I found it when researching the original RFVC question and it provides a good visual reference as to what is going on in the four stroke engine.
How Long Has The RFVC Engine Been About
The RFVC was introduced in 1983 as far as I can find out. Rock solid info on this seems thin on the ground. So tell me what you know by commenting on the post and if you have the info source that would be great. I can then update this post.