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Edelweiss Edelweiss is offline
Registered User
Join Date: Feb 2013
Location: Essen, Germany
Posts: 174
QuaLity rules !

Well said !

Originally Posted by Neil Harvey View Post
I think a lot of emphasis is placed upon boost retard in these early engines. The vacuum control certainly works, but the retard function is very slow compared to the onset of detonation.

The Classic CDI is a CDI unit that can be used with the factory timing curve set in place. It comes as factory CDI replacement still leaving the vacuum retard system in place.

However, the classic unit has the ability to recurve the ignition timing curve with the distributor locked out. Have not done this, but I cannot see why the timing curve cannot be retarded as the boost comes on as you would with any EFI system.

Whatever your max manifold pressure is, or more accurately stated, your max cylinder pressure, would be the max timing advance you could run. The timing curve would follow the cylinder pressure.

More advance at the lower RPM's and as the boost increases the timing curve would be retarded some and as the RPM increases in the higher RPM's and as the cylinder pressure drops you could add in more advance. I would think you would program a curve 2 away from knock to be safe.

Really no difference between doing this with a fixed timing curve to suit each engine or allowing the unit to retard as programmed.

Any other way requires knock control in an EFI system and even then you, the tuner has to set the noise threshold by deciding what is noise and what is detonation.

Another really important factor to consider is the quality of the CDI itself. We would never use an MSD product on any of our engines due to their manufacturing quality. Having looked inside both, the Classic unit is heads and shoulders above anything MDS sells.

Choose wisely and understand what you are actually buying in the way of features. Maybe its no better than a well tuned ignition curve.
Old 02-27-2018, 12:00 PM
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