mechanical losses from rod ratio?

[thaharlequin]

Torque is all about the force a cylinder can exert (which is directly related to cylinder pressure and disp) via the leverage the crank throw can provide? correct?
now i was wondering how the mechanical losses from the rod ratio factored in?

[Sniper]

yes, it does...sure PNG or someone can site a couple of examples where rod ratio has come into play, but here's how it all works.....

to change the linear motion of the piston into angular motion of the crank, part of the torque is indeed wasted.....the actual power travels down throught he rod, however the power that goes into the crank is only the Y- portion, and the X-portion is basically waste.....now if we use a crank with a long throw and a short rod, at 90deg, the angle of the rod gets really low(say 45deg relative)...this means that our Y- value gets lower too....now we'll take a crank with a short throw and a long rod...at 90deg, the rod is much steeper, having a greater Y-value.....generally meaning more power making it to the crank.....

so now to torque.....T = F * d.....which pretty much means our Y- * the crank throw.....back to our examples...short throw * long rod or long throw *short rod....easy to seee that these numbers could come pretty close to each other eh?........once you're to this part in the design process you have to start thinking about goals for the engine(kinda easy to see that the shorter crank will like to rev more than the longer) and the other ratios/parts/etc that will all work together......

i'm probably gonna get this post deleted for being a little too technical:rolleyes: ........

[thaharlequin]

Originally posted by Sniper
i'm probably gonna get this post deleted for being a little too technical:rolleyes: ........

no way, however if you incuded something along the lines of how the torque created thru the rev range can be expressed thru so-and-so mathmatical model which if you integrate will give you the total power created by the engine over delta t, and if you find the point where m=o...etc...
*that would be too technical :)
all you went into was simple physics...
thanks

[Sniper]

Originally posted by thaharlequin
no way, however if you incuded something along the lines of how the torque created thru the rev range can be expressed thru so-and-so mathmatical model which if you integrate will give you the total power created by the engine over delta t, and if you find the point where m=o...etc...


that's pretty much how a dyno works......

[thaharlequin]

lol, minus the mathematical modeling yeah...
oddly enough that was all random :D

[TypeIII]

In my opinion, rod stroke ratio should be more of a reliability issue rather than performance concern. You push your RS ratio far enough you're gonna have your piston pin in the oil ring area... Unless you're constant rebuilding your engine, your motor is going to burn a lot of oil.