well interal work will have to be done restoked crank maybe the answer.
Restroked to what?
I think you may have just read an issue of max power and thought something you read could be applied to every engine?
The F4R has two significant geometry problems as standard:
1: The bore to stroke ratio is poor, due to too small a bore compared to the stroke, meaning you are restricted on valve area
2: The Rod to Stroke length ratio is poor, due to a long throw crank and a short rod
If you make the stroke longer (which would be physically difficult anyway due to lack of clearance) you would then make both these things even worse.
Its just not worth doing to an F4R, unless you are planning on getting a taller block cast or a spacer installed onto the top of it and then sleeved, both of which are very expensive.
The way to get 250bhp out of a 172 engine is just to turbo it, piece of cake making that power and it will last far longer than a 250bhp N/A one too as it wont need to rev as hard.
