I finally put a timing light on my 260 in the 70S. First off, it runs great. Decent mileage and power for a 260 with NO pinging. With the vacuum advanced unplugged, it was at 36 degrees at 1000 rpm. Around 700 rpm, 30 degrees. Thinking there might be another 30 degrees added with the vacuum advance. I did one light and medium spring, unless it is advancing a lot at low rpm, it is very advanced. If it is advancing that much, then it is different than any other factory HEI with lighter springs. I could never get full advance much under 3000 rpm.

 

Odd. If I remember correctly it should be 20°@1100RPM.

 

That is my understanding as well. This 260 has that crappy little balancer, doubt if it could spin. I am of the belief that the Olds V8 loves a lot timing, this 260 is more proof.

 

Yes they like a lot of timing. My 350 is set about the same. But, you shouldn't be advancing at such a low rpm. Timing should stay stable through fast idle, then advance above that.