Greg,

Agreed, I haven't chased through the web looking for those specific values. Even Brake Specific Fuel Consumption is pretty arcane for our uses. We can measure fuel consumption per unit time, but in-air RPM is almost always an estimate, as is the prop load at the relevant airspeed. How, then, calculate brake horsepower?

The odd condition of having such blended fuels, IMHO, makes it more difficult to state reliable specifics. So much depends on the complex blend of fuel components, user factors, engine, setting, prop, altitude, humidity, temperature, phase of the moon, etc.

Not so sure I can buy the idea that "modern" schneurle engines are fundamentally different/better than engines of 10 to 15 years ago, when Mike Billinton ran engine tests for AeroModeller(RIP), and I think I'd seen some of his work in an occasional MAN since. He tested ABC, ABN, AAC schneurles more than any retro crossflow engines. Nice work. He didn't reduce torque and HP curves to idealized, smooth approximations. Still, invariably, his peformance graphs indicated torque peak RPM at moderate values, however high the engine could wind out before HP peak RPM... Exceptions, too. He also ran some tests with tuned pipe boost, and graphed the torque and horsepower consequences for several different max boost and max degradation conditions from the pipes...

So far as "effective" volumetric efficiency - it seems to me that in a given engine there is one optimal "gas-flow" zone (air and vaporized fuel being considered gaseous) where the volume transferred is optimal, where pumping losses are best countered. THIS is what I expect more rigorous, complex testing and analysis would find to coincide closely with the engine's torque peak RPM. Seems to me to be a matter tied to the internal sculpturing, paths and instantaneous flow velocities in several small zones... which we generally don't mess with... Pipe resonance effects superimpose on this 'natural' flow.

The actual compression ratios at 10K and 20K are more rather unrealistic numbers for the average user. They aren't very far apart on the compression lever, anyway. The loads involved are more concern to the engineers who develop engines, not to most of us at the user-end.

Of course, any method of ignition can serve engines designed to whatever RPM conditions are sought for. Design from blank paper (monitor screen?) works best, if your demands are very far off 'the usual'. PAW engines are pretty sturdy, to begin with, so re-engineering to withstand loads may not be a factor. Fit, clearances, sleeve and shaft timing, assembly alignment and most suitable part weights within the factory tolerance spread are easier to optimize when you have the entire batches of a production run to cull through. In addition, PAW factory surely knows what further touches to porting best serve combat and racing. The performance differences are definitely there. But PAW is not a best example of purpose-built high-RPM diesel engines. For combat, perhaps, with the local popularity in some areas of Nostalgia Diesel FAI Combat, but all first tier current FAI Combat engines are glow these days. TR diesels turn in the vicinity of 30K, and get plenty of laps per tank - now, that's amazing!

The ENYA 25 SS-D I'm breaking in shows ~10,000 RPM with about a half-hour on it, on an 11-6. I expect the factory numbers are possible, eventually, but are not ordinary flight settings. BTW, I live at ~5,000' above sea level, but diesels are less susceptible to altitude effects, or better said, the adjustments allow compensating for those better.

ADDED: Went back and read your links. John Modistach's report on the 25 SS-DTV is interesting and well written. The 25D I have is the non-TV version, although the effective choke areas are similar. Also, after the first 10 minutes on 1-1-1 fuel, and a few minutes on the 3-3-2 blend cited, I'm running 5-3-2 blend, with the 50% being kero. The VicStunt report on the FORA is interesting, too. I'd expect higher RPM... Haven't spent much time browsing VicSTUNT lately... Thanx!