How far in the hole 318 pistons

RustyRatRod said

Well, sorta. While it is true that compression dropped, it's also true that horse power ratings changed from gross to net. So that makes it appear that engines lost a ton of power from 72 onward, when in fact, they did not. That'a always a part of the equation people sometimes forget. With all else aqual, a 10:1 engine for example, will make only about 6% more power than an 8:1 engine. Compression alone isn't the end all be all a lot of people think it is.

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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.