Variable Compression, Variable Displacement you deside

Matthew B. Watts mwatts at facility.cs.utah.edu
Wed Feb 18 09:10:08 GMT 1998


To keep it simple, what we'd really like to have is 20 pounds of
boost on the intake side at no cost (no accessories) and absolute
zero pressure on the exhaust side, again for free.  Then if we
could burn the fuel mixture and generate only kinetic energy without
any heat, we could achieve 100% volumetric efficiency.  Even with
this "perfect" setup, we still need RPMs to do anything useful--valve
timing and ignition begin to work against us here.  Did I mention
friction?

Since it's very difficult to change the bore and stroke on-the-fly, one
might reason that an engine will work best at a certain RPM and
load.  Compression is closely related to the type of fuel in the mix,
which is also hard to change on-the-fly.  So separate the fixed
parameters from the ones that can be changed first.  Second,
worry about parameters that make the engine more dynamic
during normal operation.

Bottom line is that it's all a tradeoff and the application the engine
will be used for determines what combination works best.  One must
keep track of the "big picture" at all times before jumping into the
details.  From there it's all a matter of optimization...

Matt Watts
University of Utah
Formula SAE Racing
__________________




More information about the Diy_efi mailing list