906 or 915 ?

I built my first 440 for my road runner back in the day. Home ported 452 heads with stock valves, had no idea what I was doing. Car ran low 13 seconds with a comp .501 cam.

I bought a set of 915 heads with 2.14/1.81 valves that had been hogged out by a local racer… they looked great.

I had them checked at the local machine shop and swapped them out, changing absolutely nothing else.

The car idled rougher and felt more snappy around town, due to higher compression I guess, but the quarter mile times were identical.