okay, i analyzed the piston speed of an engine using the IC method (for those of you mechanical engineers out there). here is what i come up with:

piston speed =
[(engine speed in rad/s)*(1/2 of stroke length in m)]
------------------------------------------------------------------------------------------
[(rod length in m)*(tangent of angle between conrod and piston top)]
-----------------------------------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------------------------------
[(rod length in m)/(cosine of angle between conrod and piston top)]

i used the time at which the radius from the centerline of the crank to the connecting rod is parallel with the top of the piston, since this should be the moment at which the piston is accelerating the least (i presumed, didn't calculate), and therefore should have the highest velocity.
here are some results:
B18B@7000rpm: 193.88m/s
B18C@8000rpm: 201.79m/s
B16A@8000rpm: 153.09m/s
F20C@9000rpm: 132.51m/s
B17A@8000rpm: 196.35m/s

does this sound right? all of them but the F20C seem to make sense, but then again the F20C has an ungodly 1.82 rod/stroke ratio. i know i've seen destroked H22's (to 2.0L) running in the high revs like motorcycle engines in endurance racing, so maybe the F20C simply has the potential to be insanely rev-happy.

 

hehe, the reason i'm putting the f20a into my car

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by O3DigitalBath &raquo;</TD></TR><TR><TD CLASS="quote">hehe, the reason i'm putting the f20a into my car </TD></TR></TABLE>
F20A? please expound . . . F20B = Accord Euro-R

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 95lstegman &raquo;</TD></TR><TR><TD CLASS="quote">i used the time at which the radius from the centerline of the crank to the connecting rod is parallel with the top of the piston </TD></TR></TABLE>

this line made me do a double take. but then i realized that is correct. that should be the point of greatest velocity and lowest accel. that would be ~45* of rotation from tdc.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 95lstegman &raquo;</TD></TR><TR><TD CLASS="quote">
F20A? please expound . . . F20B = Accord Euro-R</TD></TR></TABLE>

its another euro accord motor, similar bottom end (lower compession) than the f20b but with a non vtec head. (tho I could always slap the h22 one on there)

 

so i'm assuming it's cheap as heck? otherwise why bother? just get an F20B? what are the stroke, connecting rod length, and redline for the F20A/B? i'll put it into the spreadsheet and post results. i'm pretty sure it's not the same. i've seen a torn down F20C and it looks like the Honda K-series, which is to say, it's built almost as bulletproof as my 1992 Nissan .

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sanimalp &raquo;</TD></TR><TR><TD CLASS="quote">this line made me do a double take. but then i realized that is correct. that should be the point of greatest velocity and lowest accel. that would be ~45* of rotation from tdc. </TD></TR></TABLE>
i just now thought about what you said, but i didn't edit my post b/c i wanted to quote you. maybe you're thinking of 45* of rotation on the camshaft, but the point at which the piston speeds are greatest are 90* in either direction from TDC (or BDC for that matter). at 45* it's less a little less than half what the speed is at 90*. now what would also be interesting would be a graph of how piston speed changes through the rotation of the crankshaft, or basically a graph of the acceleration of the piston through one full rotation of the crankshaft. problem is my spreadsheet isn't set up in a way that i can create something like that. i'd have to go back and totally redesign it, and i don't feel like it .

 

http://www.wfu.edu/~rollins/piston/

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mmuller &raquo;</TD></TR><TR><TD CLASS="quote">http://www.wfu.edu/~rollins/piston/</TD></TR></TABLE>

he's doing it in a funny way. it pissed me off. my way was MUCH simpler and quicker. thanks for the graphs though. i already figured out it was something like that by playing with my values. velocity is not quite linear leading up to max and min values. nifty nifty, thanks.

 

yeah 90* is correct.. i thought 90* and put 45* for some reason.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sanimalp &raquo;</TD></TR><TR><TD CLASS="quote">yeah 90* is correct.. i thought 90* and put 45* for some reason.</TD></TR></TABLE>
ah, thank you. i'm not crazy after all. but then i used that sign mmuller posted up and put in the same engine and got 190m/s out of my equation and 393m/s out of his equation (after converting mi/hr into m/s, which is a factor of ~3600/1620). hmmmm. and his also says max piston speed occurs at ~60* before and after TDC. doesn't make sense to me. i didn't actually look at his whole solution, but after solving through mine i found no mistakes. and when i check mine, i still get max speed at 90 degrees between crank throw and straight up (so the rod isn't actually perpendicular to the circumference of the crank throw; the crank throw is simply parallel to the deck of the motor). either way mine is consistent and precise (accurate within its own results if not accurate to the real answer) and i don't see an error, so i'll keep using it.

 

well.. his calculations are based on a different rod length and radius than what you are using, and i think this is what is causing the difference. he used the distance equation he derived to calculate, via derivative, the velocity and acceleration, which is also correct. he did get ~64* for his system, which is mathematically shown to be correct. but the dimensions are much different than what you and i are looking at for honda engines.. unfortunatly i am far away from my honda book and far away from a computer with matlab on it, so i cant do the actual calculations for us. i think 90* is still a good approximation, but the more i think about it, the more i think it is actually off. this whole time i have been thinking about the velocity of the piston as a simple parabola, but it really is not. that graph he posted labeled graph 2 is not a simple parabola, which means that the max velocity is occuring farther away from 90* than we both think. the calc he is doing is correct, and when i get back to my own computer ill figure it all out and post my findings as they pertain to honda engines.

 

yeah if i wanted to be smart i would have started out by deriving the equations. i thought about that, but it seemed to me that 90* should be the max so i just ran the dynamics (i.e. the I.C. Method) on the setup at 90*. i guess i should have started by deriving it after all. but then, i never intended to spend more than a few minutes on it.