Rod/stroke ratio, piston speeds, etc. (was: Hey my Chevy has Ford Rods !!!!!!)

[The Dupuis]

Just for kicks, I've drawn two 350 chevs in AutoCAD, accurate to 6 decimal
places.  One has 5.7" rods and the other has 6.2" rods.  I've broken
crankshaft rotation into 5 degree chunks.  Also, I found the point that the
crank and the rod are at right angles to each other, indicating peak piston
speed.  Finally, I've plotted how many degrees it takes for both engines to
"dwell" within .010" of TDC and BDC.  I'll give it to you in inches first:

At the bottom of the stroke, a piston on 5.7" rods travels 0.004870" and a
piston on 6.2" rods moves 0.005043".  At the top of the stroke the piston on
a 5.7" rod travels 0.009139" and the piston on a 6.2" rod travels 0.008967"
Maximum piston speed for the 5.7" rod is at 163.024501 degrees and with the
6.2" rod it happens at 164.323482 degrees.  Maximum piston velocity for the
5.7" rod is 0.158697" in the 5 degrees centered on max velocity, and the
same value with the 6.2" rods gives 0.157648".  At 90 degrees, both pistons
are moving the same speed - 0.151795" in 5 degrees.

Dwell time, as defined by the above, is 10.75982 degrees for the short rod
motor at TDC and 10.862748 degrees for the long rod.  At BDC, the short rod
dwells for 14.737538 degrees and the long rod motor dwells for 14.48436
degrees.

So, let's take a 6000 rpm motor.  Each revolution takes .01 seconds, and
5/360 of that is .000139 seconds.  TDC to 5* ATDC average speed for 5.7" rod
= 65.8"/sec and 6.2" rod = 64.6"/sec.  Peak piston velocity +/- 2.5 degrees
for 5.7" rod = 1142.6"/sec and 6.2" rod = 1135.0"/sec.  Piston velocity for
both engines at 90* = 1092.9"/sec.  Average piston velocity for 5* BBDC to
BDC for 5.7" motor = 35.0"/sec and 6.2" rod = 36.3"/sec.

I'm not trying to be anal, only to indicate that piston velocity is also
related to crank angle and rod/stroke ratio.

All this proves ONE thing for sure - I've got WAY too much time on my hands!
LOL!  Another thing is that in order to drop peak piston velocity from
1142.6"/sec to 1135.0"/sec costs LOTS of money, in the form of pistons,
rods, machining, etc.  Does the extra .102928 degrees at TDC justify the
long rod motor?  An extra 0.000000286 seconds at TDC???  You decide.  I'm
too tired.

Matt

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