360 stroker how much HP is picked up if everything else stays the same?
You know what’s really funny (well, made me laugh anyways!) about that statement is the engine masters 383 vs 383 where the short stroke produced more torque than the long stroke engine earlier on in the pull.
Shock the **** outta me.
It makes a ton of sense to me - piston area goes up with the square of the radius of the bore, but torque goes up linearly with the increase in throw. But rod angle takes some away from the throw increase, larger bores have few drawbacks other than production cost and sometimes piston weight.
Longer bores help to increase compression due to the larger swept area, and the longer stroke can help build more intake charge momentum and change some of the resonant tuning as a result. But otherwise, the longer stroke just causes the piston to move faster (and farther) at a given rpm, which isn't always good. Flame fronts only go so fast, and friction forces are cumulative. Not to mention that trying to flow more air into the cylinder, but with valves hemmed in by the bore is often a losing proposition.
A short stroke, large bore motor will probably always out power a long stroke motor (of the same displacement). Not to mention that short strokes can shorten the intake path, make it more direct to the carb bores, and fit larger valves. Makes for a potent combo.
I think most strokers gain their torque (and thus hp) from the longer arm and not necessarily the increased volume. The air charge can only expand so much before it becomes a diminishing return. There's a 13% difference in stroke going from 3.58 to 4.0", but the rod angle (73 vs just under 71) is about a 5% change, so maybe a final torque/power gain of 7-10% over a stock stroke, but that same 13% increase in stroke is 13% faster peak piston speed and travel distance, so more friction. Friction is a function of normal force, and not area, so a larger bore pays no friction penalty.
There's got to be a reason most modern production engines are close to the same stroke length and rarely over about 3.75 (for a gasoline powerplant).
