[Shop-talk] 6 to 3 fuel saving

[Paul Mele]

a little more food for thought

BMW 528e
M20 "eta" engine, 2.7 liters, low RPM/ high torque;
designed for fuel economy. 
the write-up discussed how the engineers at BMW targeted the valve train
parasitic drag; used 4 cam bearings instead of 7; lighter valve springs (not
mass, but spring constant), since no "hi rpm float" to worry about; higher
lift (more torque)....35 mpg in 3200 lb 5-series

M10 engine with 3.5 liters, 7 cam bearings, hi rpm, more torque, stiffer
valve springs....26 mpg in same body/ susp/ brakes

M20 "eta" engine in 325e...
about 500 lbs less weight than 528e
37 mpg
this follows rule of thumb of 1-2 % fuel consumption change for every 100
lbs weight

M20 "i" engine in 325i
same M20 engine with 2.5 liters, 7 cam bearings, hi rpm, slightly less
torque, stiffer valve springs....27 mpg in same body/ susp/ brakes
so, approx 25% diff in fuel economy with low-friction design of same engine
in same car....and same number of cylinders working.

these are all cars I own now or in the past...

Another interesting note on friction and pumping losses...
I have a FASCINATING book and DOS program called "PC DYNO"; great reading
for anyone who likes theory behind designs and compromises.  It shatters
quite a few "beliefs" that I grew up with (bore vs stroke, for instance)

and, I dropped my jaw when I read that it takes 250 HP to turn a NASCAR V8
at 8500 rpm.  Put another way, the engine makes 1100 HP, but only 850 end up
at the flywheel; the other 250 is used to turn it [ friction and pump the
air]...