It is my opinion that these cars should be in the 40 mpg range on the
highway, when in good working order and properly tuned. I have experienced
44 mpg with my 1275cc Sprite when running a constant 65 mph with 4:10 diff.
Drops to about 35 when running constant 75-80 mph. I am running stock SU
carbs and the original centrifugal-only dizzy with a fairly large cam and a
header on a carefully rebuilt engine that uses all original emissions
controls (fortunately in 67 this was only a PCV valve and the oil filler
cap). Yes, I set my timing with a timing light while standing on my head.
I have also verified my advance curve against specs, and verified by
oscilloscope that the cam lobes open the points equally. I also use
dwell-meter for setting points. New throttle shafts in carbs and a lot of
trial and error with float levels, synching, and brand-new mixture needles.
However, fuel mileage in stop and go around town sucks big-time - I assume
because of the aftermarket cam. Never have been able to find the right
combination for power, economy, and good idle with this cam. I opted to
tune for power and economy at higher RPM, because this is how I usually
drive it.
I think it's always a trade-off when you start installing aftermarket parts
( or changing / modifying /removing original parts). Too many people make
the mistake of hanging a hodge-podge of parts on an engine, and expecting
them to work well together. Often, the new combination can actually reduce
performance. Been there - did that with hot rods, when I was a kid.
Cubic inches and torque and volumetric efficiency are the key components to
best performance on the street. The 948 and 1098 owners can talk about how
powerfully their engine is built, but they will never be able to compete
with a bigger engine in usual driving.
I would very much like to try one of the large cc kits sometime. Anyone out
there using one?
What are other people's experiences with fuel economy?
Les Myer
|