Hi Folks, meant to send this to the List too. Bill
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From: ardunbill@webtv.net
Date: Mon, 2 Apr 2001 08:38:58 -0400 (EDT)
To: benettw@earthlink.net (Bill & Dee Bennett)
Subject: Re: Wasted Spark
Message-ID: <24661-3AC872E2-788@storefull-244.iap.bryant.webtv.net>
In-Reply-To: "Bill & Dee Bennett" <benettw@earthlink.net>'s message of
Sun, 1 Apr 2001 23:29:04 -0400
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Hi Bill, my understanding of "wasted spark" is anytime a spark is
produced in a cylinder and it doesn't do anything. There are many
examples.
1. For many years Harley-Davidson twins used an ignition with a coil
with two high-tension leads and a contact breaker with two cams that
avoided the need for a distributor cap. Whenever a cam opened the
points (one cam for each cylinder) a spark occured at each plug. In one
cylinder it started the fire in the usual fashion, in the other it did
nothing. With the 45 degree cylinder angle of the Harley I won't try
real quick to say what was happening in the other cylinder at the time.
2. For many years with the Japanese four-cylinder motorcycles the
ignition was two sets of points (contact breakers) with two coils, each
with two high-tension leads. Four cams so each time a set of points
opened a spark occurred in each of two cylinders, one lighting a fire,
one "wasted". I seem to recall something about which direction the
spark jumps between the plug electrodes, but this is irrelevent and
makes no difference to running. In this case the waste spark occurs on
the exhaust stroke, 360 degrees away from where the "useful" spark
occurs on the compression stroke, say 36 degrees or so before top center
at full advance. When electronics came in at first they simply replaced
the points, and kept the mechanical advance, although with cdi added
probably a better spark results, along with the capability of
computer-controlled advance. On my 250 Ninja, for example, at very high
rpm, near the point of maximum hp, the timing retards a little, since
the engineers found this was necessary for max power due to something
about the four-valve combustion chamber/compression ratio
characteristics, presumably. The performance and reliability of this
ignition is impressive (got my fingers crossed), 62K + on this bike and
the ignition has never been touched, just the other day I finally had to
replace the plugs because the gap had increased from .025" to .045" and
starting (not running) was being affected. Probably better to replace
the plugs before this mileage, but this was an experiment to see just
how long they would work on a road bike without attention.
3. Nowadays we have crank-triggered ignition with four coils for V-8s,
which works exactly the same as the four-cylinder bike above, firing two
cylinders at once, with a waste spark on one, and computer-controlled
advance which I gather can be manipulated in various ways. My Lincoln
Mark VIII engine has this stock and probably other engines do too, it's
the thing now.
Regards, Ardun Bill in the Dismal Swamp where it's hayfever season.
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