Spridgeteers,
Let's all take a deep breath. This is supposed to be fun!
OK, back to the original question. How does one increase torque
output on a BMC A series engine? In my case, the engine is a 1275
with 40 overbore and a Kent 266 cam. However, I hope that what we
discuss could be applicable to all spridget motors.
One response was that intake gas velocity must be kept high. How does
one do this? Vizard, in his inimitable way, shows the use of long
(15+ inch) ram pipes with detailed discussion, but then mentions that
none of this will really work with twin SUs. I don't understand why.
But, is the only answer to switch to a single carb setup? As close
readers of his book probably know, he spends most of his effort in
increasing flow to increase ultimate power. Does anyone know of other
sources of opinion backed by real data or anecdotal experience?
Also, according to Vizard's charts, it is not necessarily always true
that a modification that increases power at the high end results in
loss of torque at the low end. Several of his charts show that torque
often increases with flow. What does seem to occur frequently,
though, is that that the power increase is proportionately larger
than the torque increase. However, his data are all a little suspect
for purposes of this discussion in that his goal is nearly always to
increase power and let torque take care of itself; he doesn't
systematically study torque. Of course, some would argue that he
doesn't systematically study anything.
Another response was to go with nitrous or increase capacity. The
nitrous idea would be fun but maybe hard on the engine. It may be
hard on the wallet. It does sound fun, though. Increasing capacity is
something for engine rebuild time. I have upped mine a bit (to a
calculated 1312 cc, I think, though the recent thread on cylinder
volume has me second guessing). One downside, in addition to cost and
time off the road, is that as the size increases, the engine does not
idle quite as smoothly - it's the one advantage I've ever heard
discussed about the 948 vs 1275.
A final response was to go with supercharging. Now _that_ is
expensive. But, it sure seems like the way to go for increase torque
and power, particularly as complete, new systems can now be bought
off the shelf (from MM and from the group in Australia). I'd have to
win the lottery, though, to go this route.
Anyway, there it is. I guess I'm looking for sub-$300 DIY torque
solutions. But mainly, I'm simply ignorant to the extreme on this
topic and would love to hear your thoughts on it.
Thanks,
Jeff
_____________________________________________________________
Jeffrey H. Boatright, PhD
Assistant Professor, Emory Eye Center, Atlanta, GA, USA
Senior Editor, Molecular Vision, http://www.molvis.org/molvis
mailto:jboatri@emory.edu
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