Teach me please! 906 heads

[Ranger16]

I hope I am not hijacking this thread, but can someone explain the difference between 906 & 915 heads and what engines they where used on?

 

[Cranky]

The 906 is an open chamber head that came out for the 68 model run on both the 383 and 440. Without digging into my old DC book, the 915 was introduced in 66 with the small exhaust valve on non performance engines and had the larger exhaust valve for the performance engines...mainly the 67 440's and were closed chambered. I've read reports where the 915 large valve heads were installed on some 383's. I think this may have happened when the run ended on the 516 head which is also a closed chambered small valve head.