I don't know what the stock bore and stroke is on a flathead, but I can give you some numbers for a clone. A .030" bore increases the displacement by about .002%. This will decrease the compression ratio by .017. Assuming everything else stays the same, such as the position of the piston, in the hole.
There's a whole lot of things to consider and you may have to change some things. A bigger bore gives you more CC's yes, but also affects compression ratio and the CC's in the combustion chamber. A bigger piston will also effect the balance of the engine. A heavier piston would mean that the engine will balance at a lower rpm.
There's so many things that get affected by a bigger piston, it's hard to say how much it will affect the horsepower.
A bigger bore may not be the answer, there may be other things to consider.
There are two popular sayings; 'there's nothing like more cubic inches", and "compression is the Holy Grail". Both are very true.
Tell me your present bore and stroke, along with combustion chamber CC's, head gasket thickness, and how far the piston is in the hole, and I can give you a closer set of numbers.
From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory. (Al Nunley)
