If we're talking about level of technology, the total thrust of an engine doesn't tell us much. The figures that tell us about technological level are T:W ratio, average HPC compression ratio, and turbine inlet temperature. Any country that can design an engine with the EJ200's specs can design a larger version in the class of the F119 or better. In fact, to some extent scaling up a smaller engine design is much easier than shrinking a larger one.
I think you have it backwards. You can downsize easily but increasing the scale of an engine requires material and design improvements just like you can make a smaller airplane from a larger design but if you upscale a smaller design without changing it, it could fall apart from stress.
If the EJ-200 is "a bit more advanced" than the WS-15 and the 2025 rumor is true, then China's engine industry is in serious trouble ... if that were the case, the Chinese engine sector would be 40 years behind the West's
Increasing the size of the engine also means increased thermal efficiency, and jet engines are fundamentally function by drawing more work out of thermal energy. With the EJ200, you could ease up on some of the mechanical demands when upsizing and still get an F119 class engine. Anyways, I did suggest that there was a limit to which this logic holds, but building an F119 class or better engine out the technology in the EJ200 falls well within the parameters of that logic. Also, RC "turbofan" engines aren't actual turbofan engines.
Well the J-20 does have a kaboose made for a slightly larger engine than WS-10X (WS-15) so for a certain amount, you could upscale say 15% for 15% more thrust without needing to expand the jet, which is no trivial amount. That they didn't makes me think that you cannot upscale engines without material/technology breakthrough.
And that is why some people make that argument. However, consider this. The WS-15 was first spec'ed out in the early 2000s using that period's technological base. It seems unlikely to me that as China's technological knowhow has improved through the years the WS-15's development team wouldn't be continuously folding in as much new knowledge and new technology as they could without having to go back to a full clean sheet or risking major disruptions in the program. Ultimately though, there's a limit to how much extra advancement you can wring out of a continuously revised concept that is a decade or two old. It may be that when China begins work on their next generation engine its technological development won't start where a completed WS-15 left off but wherever the technological base is when they start, which could be some steps ahead. It may even be that such a program could start before the WS-15 is complete. This is rather typical of situations where the technological base is moving faster than the product cycle it's being utilized in. If there really is an improved iteration of the WS-15 that is already being worked on in parallel to the current development of the WS-15 as some rumours might suggest, this would be suggestive of exactly this phenomena. I'm not saying that this is actually the case of course, just that this would be the more optimist scenario.
The limit isn't the kaboose. It's the intake. And the point isn't to get 15% more thrust through upscaling, but to get that 15% increase in thrust to weight ratio through upscaling, which could require a lot more than a 15% increase in size. This is all academic of course. There are a lot of limiting factors to the logic, and it wasn't my intention to make a straight extrapolation with this point.
Obviously you would need material enhancements to maintain the same level of mechanical performance for a larger engine, but my point is that with a bigger engine you can get more performance with less demanding mechanical performance.
Actually, China also has the ability to produce high thrust turbofans. But my response to Latenlazy was that if the WS-15 was indeed inferior to the 80s EJ-200, then there is a huge problem. A generation and a half gap is huge in the modern day aviation industry .... and imagine that gap in 2025. The WS-15 Should at the very least be on the same level as EJ-200 or M88-3 if it wants to close the engine gap. How will the WS-15 compare with an upgraded F-135 in the future then? Maybe we are relying too heavily on a 2004 academic paper but if the WS-15 has the exact same parameters ... then the wait will be troubling. We can only hope that it is because of technical improvements that the WS-15 has been delayed ... the WS-15 dev cycle should be faster than that of the WS-10.