twinrock Posted January 21, 2007 Report Posted January 21, 2007 hey ive heard a bit about strokin engines..but not sure how it works,,as far as i can work out ..by changing the lenght /stroke of the crank u increase the cc of the engine?? can any one shed more light on the subject..ie what size cranks give what cc and what else is needed and how eficient it is..thanks.. Quote
odaen Posted January 21, 2007 Report Posted January 21, 2007 hey ive heard a bit about strokin engines..but not sure how it works,,as far as i can work out ..by changing the lenght /stroke of the crank u increase the cc of the engine?? can any one shed more light on the subject..ie what size cranks give what cc and what else is needed and how eficient it is..thanks.. Stroking a motor is just putting in a crank with a longer stroke........yeah, increasing displacement. There are some easier formulas to use, but they are based on the following (.5 x bore)^2 x 3.14 x stroke x # of cylinders / 1000 stock stroke for a banshee is 54mm, so a 4mm crank is 58mm stroke and so on stock bore is 64mm for a banshee .020" is approximately .5mm, so a motor that is .020 over is 64.5mm bore Quote
theshee Posted January 21, 2007 Report Posted January 21, 2007 I think I have read somewhere a 4 mil crank is a 7% increase in power... Some one chime in if this isnt correct but I think thats what I have read before. :thumbsup: Quote
odaen Posted January 21, 2007 Report Posted January 21, 2007 I think I have read somewhere a 4 mil crank is a 7% increase in power... Some one chime in if this isnt correct but I think thats what I have read before. :thumbsup: That's probably about right. The 7% number is most likely just what they calculate the displacement increase to be. 4mm is about 7% of 54mm. Quote
dajogejr Posted January 21, 2007 Report Posted January 21, 2007 My friend posted that 7%, rough figure...and he's got more time on a dyno than most people when it comes to different motor combos, stock to big stroke/bore cheetah motors.... Quote
twinrock Posted January 23, 2007 Author Report Posted January 23, 2007 ok..so does this mean i could just change the rod length..say if i was rebuilding a crank from scratch? ie i know rd400 crank is 4mm longer but has same piston size as a banshee? and i would assume it would be better to use a bace plate as to keep ur piston lined up with the exaust port? and am i correct in saying that the displacement of the engine includes the crank case as this is the area/below the piston/ that increases in volume? thanks.. Quote
odaen Posted January 23, 2007 Report Posted January 23, 2007 ok..so does this mean i could just change the rod length..say if i was rebuilding a crank from scratch? ie i know rd400 crank is 4mm longer but has same piston size as a banshee? and i would assume it would be better to use a bace plate as to keep ur piston lined up with the exaust port? and am i correct in saying that the displacement of the engine includes the crank case as this is the area/below the piston/ that increases in volume? thanks.. man, alot to break down in that question... rod length has nothing to do with stroke and has no effect on displacement some builders recommend spacer plates, others recommend cutting the domes or head to allow for the piston to rise above the deck. displacement is not effected by crank case volume. displacement is the a measure of the volume that is displaced by your piston as it rises and falls within the cylinder(s) Quote
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