Street Ryderz
Well-Known Member
I had been waiting on a replacement top end kit for a sthil ts420 that needed done due to a crank bearing failure from insufficient oil been used and had said I would compare the case volume difference between our case and the sthil's case.Now let me just say for over a year now I've tried to point out that the pumping pressure or ccr makes a huge difference when case volume is increased losing valuable pressure.This pressure is what pumps the pulled in a/f mix up the transfers but also how well it does it's job as a blocker to reverted pipe pressure behind the vac and ahead of the pulse wave and this is what insures proper cylinder fill below the pipe since when all is timed right the pipe over fills the cylinder thanks to the blocking pressure. Our case volume (bicycle engine) is over 600 cc's with equates to a ccr of around 1.12 and the still case is just over 200 cc's and that equates to 1.49 and that's HUGE I don't care what any of these guy's say there is no way that it can make the same or more power with a lower ratio! The difference between 1.12 and 1.49 in p.s.i. is 3x the pressure, from 3 p.s.i. to just over 9 p.s.i. and trust that makes a difference,here are some comparative photos for all to see the physical difference in case area and crank size.