Educate me on piston speed, bore vs stroke

[64duc]

 I used to shift my '64 250 cc Diana at 10,000. Never reved till it floated, but if I missed a shift it would float. I know that because I was running the slightly shorter Monza cyl, and every time I missed a shift [before I shimmed the cyl .010 ] it would bend the intake valve.

[zarn02]

<snip>and every time I missed a shift [before I shimmed the cyl .010 ] it would bend the intake valve.

[brad black]

the last of the 999F motors were going to 13,500 or so i think, and the 749R motors were going to 14+.  They ran tapered style collets and ti valves and still had fairly hideous cylinder head replacement intervals.  of course, some of the corse cams are actually concave on one side, and look like a parallel sided oval which doesn't help.  so desmo heads are not unlimited in rpm - there's still a point at which it all goes bad.

but the valves are bigger than 4 cyl valves - 11198 are 44 or so i think, most 1000cc 4 are 33 or 34mm, and that makes a big difference in comparative weights.

there's two ways to make power - capacity or rpm.  if one is limited, you go the other.

[Lord_Bragle]

Because air's elastic the piston in a short stoke engine is more effective at pulling air, if the stroke is half the distance it means only half as much elastic air medium has to be stretched through to pull the charge in to the cylinder.

[brad black]

for a given capacity the reduced stroke is offset by the larger bore, so wouldn't the actual inflow rate in volumetric terms be otherwise the same?  the stroke/rod length ratio does affect the rate of piston movement relative to crank rotation over the movement from tdc to bdc, but that's another variable.

[64duc]

  More than you will ever want to know about piston speed, exhaust tuning  etc.   





http://www.engineersedge.com/engine_formula_automotive.htm

[zarn02]

http://www.engineersedge.com/engine_formula_automotive.htm

Holy formulas Batman!

[junior varsity]

its all about piston speed, acceleration (and derivatives thereof: jerk/snap), and flame-front size constraints

i got to do quite a bit of research on these principles as an undergrad. I had a lot of fun doing that kind of stuff

[NorDog]

http://www.engineersedge.com/engine_formula_automotive.htm

Okay, I'm stuck in a perpetual loop.

The HP formula requires a value for "Brake Mean Effective Pressure".

But the BMEP formula requires a value for HP.

[ducpainter]

Okay, I'm stuck in a perpetual loop.

The HP formula requires a value for "Brake Mean Effective Pressure".

But the BMEP formula requires a value for HP.

Do like every engineer...

make shit up.

[Triple J]

Without being familiar with the equations, I'm guessing it is an iterative solution. Guess at a HP to get a BMEP, then use that to calculate BHP. Keep tweaking until the HP # from both equations match...then you have the true answer.

Something I am familiar with --> A similar process takes place when we calculate the external buckling pressure of a large diameter steel pipe that is restrained by backfill (usually concrete in a tunnel). Not all values can be calculated simply. 

[ducpainter]

Without being familiar with the equations, I'm guessing it is an iterative solution. Guess at a HP to get a BMEP, then use that to calculate BHP. Keep tweaking until the HP # from both equations match...then you have the true answer.

Something I am familiar with --> A similar process takes place when we calculate the external buckling pressure of a large diameter steel pipe that is restrained by backfill (usually concrete in a tunnel). Not all values can be calculated simply. 

without looking up all the big words...

I'm guessing you're right.

HP is a target and you use the other variables to determine if you can reach it.