Hey my Chevy has Ford Rods !!!!!!

[David Hunt]

To visualize the effect draw a circle of 3.48" diameter and then draw a
point that is 5.7" away from the center of that circle.  Then draw tangent
lines between the circle and the point.  I believe, but am not sure, that
these two points represent half stroke for the piston.  There is more crank
duration for 50% piston travel at the bottom half of rod big end travel,
therefore the piston travels further and faster.  At the top half of the
throw the piston travels less far and takes less time, thus more duration
and less speed.

Now, draw another line 6" away from the circle and on the same heading and
draw those tangent lines.  The piston movement between 10 degrees BTDC and
10 degrees ATDC is slightly (and ever so slightly) less in the case of the
6" rod.

Of course, the flip side of that is that there is less mechanical advantage
also.  The same amount of cylinder pressure with less piston movement means
less torque transferred to the crankshaft.  Like everything else, it's a
give a little take a little sort of deal.

Opinion here:  I believe that the effects of a long rod are MUCH more
important on a high compression engine where the (minimal) effects of longer
duration allow more pre combustion fuel heating and thus more combustion
propogation in the critical first few milliseconds before increased wall
heat losses of greater cylinder wall exposure tries to put out the flame.
Or in the terminology of Mr. Carnot, the effective combustion temperature is
increased which increases the total thermal energy spread between maximum
and ambient temperature.  Well, at least for some of the combustion
products.  Fast burn technology is another method for accomplishing the same
goal, that is mix the fuel and keep it hot so that it will burn completely
and quickly and hotter.  Of course, once again, if the fuel gets very hot
and pressures very high near TDC little is gained if those pressures are
lost before the crank is turned to maximum mechanical advantage which is
about 90 degrees ATDC(Power.)  Voila, warm cylinder walls and cool heads.  I
beleive that temperature control is much more important than long rods.  One
cost 10's of dollars the other costs 1,000 of dollars.  The important one
costs 10's, but there is little profit to be had.  And for heavens sake put
that thermostat back in!



Date: Tue, 08 Jan 2002 06:33:24 +0000
From: "The Punisher" <punisher454 at hotmail.com>
Subject: RE: Hey my Chevy has Ford Rods !!!!!!

Huh??  I always thought that longer rods would allow the piston to dwell
longer at the end of the stroke (top and bottom) and therefore have a higher
speed while traveling up and down. How can it dwell longer at the top AND
move slower too??? did I just mis-understand you or am I missing something
here ?




----- End of forwarded message from owner-diy_efi at diy-efi.org -----
----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org