How far in the hole 318 pistons

A38Valiant said
One thing to remember is that factory ratings were just that, ratings. Not actual measurements. 68 and 69 318s have an advertised 230 horsepower, and an advertised 9.25 ratio with open chamber heads. A 70 318 is still advertised as 230 horsepower, with an advertised 8.8 ratio. A 71 318 still advertised 230 horses, but ratio is now 8.6. So the math says half a point less compression, at a theoretical 3 percent per point, should be a minimum of four less horsepower.

There could be a number of other factors involved that the factories could have used beside fudging the numbers. Camshaft profiles could be one. Lower intake lift but longer duration is one I found in the TRW cam catalogue. This applied to Mopar, Chev and Ford bread and butter engines of the day. That was 30 years ago I found that, so it may be difficult to track down now.