See teema ei pruugi teile vajalikku infot anda kuid postitan siia siiski mõningaid valemeid, mõttekäike jne mida pean vajalikuks kuhugi talletada et need vajadusel üles leida. Jätan need esialgu originaal keelde, et välistada võimalikud valesti tõlgendamise võimalused.
Miks Bore on liitri jõu taga ajamisel olulisem kui stroke:
John Maher:
Increasing bore and reducing stroke delivers two significant benefits to a high rpm race engine… the shorter stroke reduces piston speed and the larger bore makes room for bigger valves…..
Imagine a theoretical drag race series dictating a maximum capacity of 2276cc (normally 82mm x 94mm). If the rules allow any combination of bore and stroke I’d be looking at say a 101.6mm bore rather than 94mm, and reducing stroke from 82mm to 70mm (2270cc). A set of suitably modified 101.6mm heads would easily outflow anything you could fit on a 94mm bore engine.
Second major gain is a reduction in piston speed. At 7000rpm, an 82mm stroke motor has an average piston speed of 3766 feet per minute. Reduce stroke, the piston has less distance to travel in the same time and speed falls to 3215 feet/min for the 70mm crank at the same rpm. Therefore higher rpm is on the cards with the 70mm stroke and the bigger ports and valves of the 101.6mm heads can make some serious power, assuming they’re teamed up with suitable cam, induction, exhaust etc
Horsepower lost to friction is also a factor with approx 75% of an engine's friction hp being caused by ring to cylinder contact. The reduction in stroke more than offsets the extra contact area of the larger diameter rings so more power is being used to turn the engine than being lost as heat.
Currently there’s no real incentive to persuade someone to build a short stroke, big bore n/a engine because having a higher bhp/litre ratio isn't going to win you the race if the guy in the next lane has more total bhp. But if you're looking to maximise bhp/litre, IMO this would be the route to explore.