[alfa] Cam drive power

[bearbvd@xxxxxxxxxxxxxx (Greg Hermann)]

I sort of snorted last night, as did someone else, albeit a bit more
politely, at a couple of comments about how much parasitic power might be
saved by going from a double row to a single row timing chain.

Since then, some facts on the subject have come back to me.

While at Morse, I was ALSO involved in development and testing for the
timing belt for the 4 cyl, 2300 cc Chevy Vega engine.

We designed and built test machines for testing said belts. Per data
obtained DIRECTLY from GM's engineering people, the load on the camshaft
sprocket was 1.1 HP at 5000 crank (2500 cam ) rpm. The GM people had
arrived at this number via actual testing--with an electric motor driving
the cam in a fully assembled head (valves, springs, followers, etc.--all in
place, and the head properly oiled, as it would be in an operating engine.
GM had absolutely NO motivation to either over OR understate this power
number--their only interest at the time was in developing a belt drive for
the new engine's cam that would WORK, reliably.

For those who never knew, or do not recall, the Vega 2300 was an I-4 with
an Al block and an iron head, with eight valves, in line, a single overhead
cam, and inverted bucket followers. The cam bearings were rather larger
diameter than those on an Alfa, as they were large enough to install the
cam through them from the front--no removable bearing caps, as on Alfas.
Typically--the larger the diameter of a plain bearing, the more friction it
generates--so, I think, if anything, the power consumption of the Vega cam
set-up might be a wee bit higher than that of an Alfa's.

Next---based on quite a _LOT_ of well controlled testing--roller chain
drives are a VERY efficient power transmission device. Typically they offer
efficiency in the range of 98% !! Note that this is higher than the
efficiency gears offer.

So--if we figure that it is going to take about 1.1 HP to drive the cams in
an Alfa engine at 5000 crank rpm, and calculate the magnitude of the power
loss in the chain drive (2%)---we come out with 1.1 x .02 =0.022 HP worth
of power loss in the chain drive to an Alfa' cams. EVEN if a single row
chain were capable of transmitting the needed power with, say, 20% less
power loss ---then the savings involved would come to a _GRAND_  total of
0.0045 HP !!!

Hence, my snort reaction of last night, although I freely admit that I did
not bother to quantify the reason for my snort until today !!! Now perhaps
the rest of you can share in a hearty guffaw !!!

Admittedly, a single row chain IS lighter than a double row (although NOT
by 50%) --so going to a single row chain would reduce the 'rotating'
inertia of the engine marginally, with the concomitant effects on throttle
response and vehicle acceleration, particularly in the lower gears.
HOWEVER--the sprockets really aren't very big, so chain speed isn't all
that high.

There would be a LOT more profit in going to a lighter flywheel and a
custom crank with features such as hollow (drilled) rod journals and
profiled, 'swiss-cheesed' counterweights than would ever exist in playing
with the poor chain.  Furthermore--the crank and flywheel tricks wouldn't
reduce the engine's reliability the way a single row chain would.

One last point: in one of my messages yesterday, I mentioned that the
biggest gain to be had in chain reliability would be had by procuring the
appropriate tool, and pressing the last link of the chain together, rather
than using a master link.

This was _NOT_  idle chatter!!!!

Master links are FAR weaker in fatigue life than any other part of the
chain !!! This is true because the usual press fit between the pins and the
pin-link plates 'pre-stresses' the portion of the plates surrounding the
holes, and thus inhibits the initiation of fatigue cracks.

Greg
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