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From: phil@osiris.UUCP (Philip Kos)
Newsgroups: net.auto
Subject: Re: SAAB IGNITION BREAKTHROUGH
Message-ID: <189@osiris.UUCP>
Date: Wed, 20-Mar-85 14:46:32 EST
Article-I.D.: osiris.189
Posted: Wed Mar 20 14:46:32 1985
Date-Received: Sat, 23-Mar-85 00:22:53 EST
References: <264@eneevax.UUCP>
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Organization: Johns Hopkins Hospital
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> I'm just wondering ... is the sensor looking at the crankshaft
> or is it looking at the camshaft ... seems to me that the
> camshaft would be more appropriate since it's spinning at
> half the speed as the crankshaft. A few manufactures are now
> running the distributor directly off of the camshaft.

The sensor could look at either.  Just because the crank is spinning
twice as fast as the cam doesn't mean it won't work - you just put
two lobes on the distributor point cam instead of four (or however
many cylinders your engine has).

As for running the distributor off the cam instead of the crank,
this has been the way it's done for years, because the distributor
classically turns at the same speed (in rpm) as the cam, which is
half crankshaft speed in a four-stroke engine (1:1 gearing).  The
same distributor could be driven off the crank with a 2:1 gearing
reduction, or a different distributor (with half as many lobes on
the point cam) at 1:1.  Sounds like Saab is probably using the 1:1
crank drive with two lobes instead of four.

Of course, for 2-stroke engines, all this changes.

					Phil Kos
					The Johns Hopkins Hospital