OT max economy, engine stress

[Gary Derian]

Actually heavier component would have the inertia required to offset the gas
loads.  When the piston is in the top half of its stroke, the rod is in
tension because the piston is slowing from peak velocity upwards to a stop
then accelerating to a peak velocity downwards.  Gas pressure pushes the
piston down and depending on the rpm, either relieves the tension in the rod
(high rpm) or compresses it (low rpm).  The heavier the piston the higher
the rod tension and the more gas pressure you can have without buckling the
rod.  Of course on the overlap stroke, the rod sees full tension since there
is no gas pressure.  You have to model the engine components and know the
strength of your parts and then come up with a boost vs. rpm curve that
doesn't break anything.

Heavy parts will allow more boost at low rpm but will limit max rpm and
therefore max power.

Gary Derian <gderian at oh.verio.com>



> In regards to the Statement about "Nearly WOT at low rpm is the key to
> good economy.....load the rods and pistons though because their inertia
> cannot offset the gas"
>
> If what you say is true, then wouldn't lightweight aluminum or alloy
> connecting rods as well as lightweight alloy pistons and pins help to
> offset the inertia prob you are referring to?
>
> Todd....!!
>