On Mon, 10 Aug 1998 21:30:10 EDT DANMAS@aol.com writes:
>In a message dated 98-08-10 19:30:27 EDT, Bob MGT writes:
Dan and Bob,
If I said or lead one to believe that the plug towers are wired
parallel, I was definitly wrong. They are wire in series (if that means
they would fire at the same time).
Harley Davidson used a low-tech version of this for years on both the
Big twin and the sportster. The bikes used one set of points, no true
distributor, and a "special" coil that had two HT towers; one for each
plug. Each time the points opened, both plugs fired, one on the
compression stroke for the firing cylinder, the other on the exhaust
stroke of the other cylinder. There really wasn't an advantage from a
performance standpoint, rather it was a manufacturing advantage. With the
twin coil, the point cam ran at crankshaft speed,and eleminated the need
for either a second set of points or a true distributor. A savings in
manufacturing costs and complexity.
Modern cars, running "distributorless ignition" or Crankfired ignition
systems do so for basically the same reason. By fireing two plugs at the
same time, 180 degrees apart (crankshaft rotation) with one being a
"wasted" spark on the exhaust stroke, the number of sensor points (either
magnetic, hall effect or optical) is reduced by half and allows the
sensor to be driven by the crankshaft, instead of the camshaft, if each
plug were to be fired independently, which would require 8 coils (on a
V8) instead of 4. Plus one benefit of the crankfired system, namely the
greater precision, would be to a large extent lost by having to run the
sensor off the camshaft; you would have most of the timing variations of
the distributor system due to the "slop" in camshaft drive, flex, etc.
Again, we are back to reduced manufacturing costs and complexity. (while
the manufacturers tout the crankfired system as being installed as a
performance enhancer, you can bet your bippy, the prime reason is reduced
costs! the reliability and precision is a happy coincedence)
By the by, there is availible a crankfired ignition system availible to
fit LBC's. A couple of the racer outlet carry them, and considering what
you get, the cost isn't all that bad, somewhere in the 500-600 dollar
range for the complete setup.
Rick Morrison
72 MGBGT
74 Midget
>
>Good point! It makes a lot of sense, yet if the high tension leads to
>the two
>plugs are connected at the HT lead of the coil, as Rick Morrison
>stated (or as
>I understood him to say), then they are wired in parallel. I guess
>I'll have
>to do a little more digging. Looks like I'm going to have to forget
>everything
>I know about traditional ignition systems (which ain't very much), and
>start
>learning all over again.
>
>Thanks,
>
>Dan Masters,
>Alcoa, TN
>
>'71 TR6---------3000mile/year driver, fully restored
>'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion
>- see:
> http://www.sky.net/~boballen/mg/Masters/
>'74 MGBGT---3000mile/year driver, original condition - slated for a V8
>soon
>'68 MGBGT---organ donor for the '74
>
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