Exactly.

I don't where or when this idea surfaced that a 50 should turn a 24-8, but thats too much prop IMO. DA claims their 50 will turn a 24-8 AFTER break in. And then I read about guys using the 24-8 after 2 tanks and wondering why the engine is running hot.

You should be using a 20-10 or a 21-8 on that Sachs 3.2 Maybe a 22-8. Anything more than that is over propping it and will lead to excessive heat--no matter how much oil you run.

These old Sachs engines are industrial cylinders. Originally designed and ported to run upwards of 10,000RPM in a chainsaw. Prop it to run at least 7000RPM or better on the bench. I wouldn't go over about 7500--7800RPM on the bench.

So, you buy props and you experiment untill you find the one that makes the most thrust at those RPM and then you live with it. That's all the work that the engine is capable of doing.

Propping one of these industrial cylinders for 6500RPM is just going to make it hot and your cheating yourself out of the HP that it can produce with 1000 more RPM.