Martin, Brian, Jens,


The question is 'how big is too big?'.

I know Diesels, for all the various reasons, even when they are converted glow engines, peak significantly lower in the RPM range than equivalent glow engines.

I also know that by reducing the compression, pre-ignition and thus overheating can be easily prevented.

But are you getting what you bargained for?
Even a Diesel has a horsepower curve, which peaks at a certain RPM level. To get the best performance out of your Diesel, you would want it to just reach its HP peak, when unloaded in high speed flight.

If a glow engine peaked (actually - not according to its manufacturer...) at 14,000 RPM and its Diesel conversion, with the smaller carburettor and all, peaks at 12,000 RPM. And you prop it for 8,000 RPM, it will unload in flight to 9,200 RPM...

This is still a good distance from making its best performance. It may even be short of the peak of its torque curve...


So reason is what is needed here. You can use a good HP calculator, to plot the HP curve of your converted Diesel.
You do it by taking tachometer readings on various props (many sizes) and entering them into the HP calc, to calculate the HP@RPM.

Using a typical glow .91 size 13x8 prop, on a .40 Diesel? It seems like overdoing it to me.


I can send the Prop Power from Pé Reivers, if you have an electronic spread-sheet program and send me your E-mail.


I have not made my .49 MVVS conversion run properly yet... It may be that my ether.... isn't...