Well, thanks Miles. Now I need to study what you have written. You've
provided more info than I can assimilate in one reading!
Thanks for all the effort.
Larry Hoy
>-----Original Message-----
>From: owner-vintage-race@autox.team.net
>[mailto:owner-vintage-race@autox.team.net] On Behalf Of
>MHKitchen@aol.com
>Sent: Saturday, July 07, 2001 3:07 PM
>To: larryhoy@prodigy.net; vintage-race@autox.team.net
>Subject: More Ignition Answers...
>
>
>I'll try to address Larry's questions ...
>
>WRT what are CDI, what are Inductive...
>
>Most newer ignitions are inductive. Some of the early MSDs
>were CDI-based,
>but I believe the later ones are now inductive multiple spark,
>or at least
>provide energies comparable to inductive systems. The early Magneti
>Marelli's were CD's, as were the old Delta Mk 10's (or
>something like that).
>Most everything else is inductive. Anything saying CDI on it is not
>inductive.
>
>Most of the breakerless ignition conversions (using either
>hall-effect,
>magnetic, or optical sensors (like the Perlux Ignitors, or
>Hayes, or Accel)
>are inductive storage. All a breakerless inductive storage
>unit is doing is
>replacing the points with a transistor switch to turn the
>current on and off
>to the ignition coil. The points used to do this with the cam
>and rubbing
>block, and the condensor was there to minimize the arcing and
>erosion on the
>contacts when you interrupted the circuit. The condensor is
>now inside the
>electronic units. The other function they provide is
>computation of the
>dwell (the amount of time the coil is ON and current is
>flowing). It takes
>an appreciable amount of current and time to "saturate" the
>transformer
>inside the coil. The longer you run the current, the more
>energy available
>to make a spark. As the rpm's increase, the time avaialable
>to do this gets
>quite short, as you still want to have a spark for at least 1
>msec (on an 8
>cyl engine at 7,000 rpm, for example). So, you need to turn
>the coil back on
>as soon as possible to reach maximum current. At very high
>rpms, you don't
>reach maximum, and thus the energy decreases with increasing rpm.
>
>You're correct on the basic assumption that the ignition
>doesn't really add
>any power to the engine. If you get the mixture lit properly,
>and it burns
>completely, then you're making maximum power.
>
>But its not always that clear cut. Over the entire rpm and
>load range, the
>demands of the engine, and the fuel/air mixture flow patterns are very
>complex. Many SAE papers have been written on the subject,
>and its still
>hotly debated today. The latest technology is optical sensors
>that can
>actually "look" at combustion taking place in the cylinder and
>adjust the
>fuel injection and timing accordingly to manage the combustion process.
>
>Usually, lean makes power, but as you know, when its too lean,
>you detonate,
>and burn holes in important parts! So, keeping combustion at
>the right level
>is critical. The ignition is part of what does this. It lights it
>initially, and may relight it again, or several times before
>the process is
>complete in that cylinder, and the piston has reached bottom.
>The flow of
>buring plasma is a science in itself...so the simple ignition
>has quickly
>elevated into some complex thermodynamic physicss issues!
>
>It's safe to say a high energy spark has a very good chance of really
>agressively lighting off your mixture, where a wimpy or short
>spark could
>light it, and then have it go out again (what happens when you
>have a fouled
>plug). This is usually noticeable. CD ignitions used to be
>popular on older
>engines that had oiling problems. The CD could fire through
>the oil, but as
>engines ran leaner and leaner, the CD's very short spark
>(about 1/10 the time
>of an inductive one) was just not enough to keep the fires lit.
>
>Personally, I run an old Homer Howard multiple spark inductive storage
>igniton. Its breakerless with a hall effect trigger, and has
>proved very
>effective. Homer's no longer with us, having passed away
>several years ago,
>and no one took over his business that I'm aware of. The real
>benefit of
>breakerless ignitions for racing, is that they eliminate
>constant adjustment.
> Just set the distributor and forget it. For this, any of the
>aftermarket
>inductive breakerless systems should be fine, as long as they
>prove reliable
>in your particular applicaiton's environment.
>
>One other point to mention is ignition timing. When you
>replace points and
>condensors with breakerless ignitions, you have a high chance
>of changing
>your advance curve.
>
>First, the points rubbing on the cam used to load the
>mechanical advance
>mechanisms. When you remove that mechanical load, the advance
>mechanisms may
>not advance the same, and/or "bounce" at low (idle) rpms,
>causing problems.
>
>If you use a magnetic reluctance type sensor (the coil and
>magnet type, NOT
>hall effect) you also introduce a characteristic retard at
>higher rpms. This
>is an electrical effect of the inductance of the sensor's
>coil. It cannot
>provide a straight line advance curve like the points did, and
>will always
>have less total advance than the mechanical mechanism offered.
> You can only
>compensate for this by introducing greater initial advance,
>and/or completely
>recalibrating the mechanical advance mechanisms for the
>particular sensor on
>a distributor machine.
>
>Regards,
>Myles H. Kitchen
>1965 Lotus Cortina Mk1 #128
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