Distributor 1967 to 1974 Application Info

Couple of updates and thoughts:

My understanding of dual points agrees with BillD, in most cases. The two sets of points are both operating during each firing event, one to start the event and one to end it, allowing greater dwell time. However, the old Mallory "Double Life" that was the Group 19 distributor operates on a different principle. The two sets of points would each trigger 4 cylinders. This allowed for a higher dwell time and also it meant that each set of points was working at half speed. Point bounce was highly unlikely, since the points were effectively only seeing around 2500-3000 rpms.

As for the pole pieces, I took a close look and checked my notes and here is an update:

I have two of the 11106 units. The first was in my car when I got it and had pole piece 724 and a date coast of "6M15". The other was date coded "8E16" and had pole piece "732". I suspect that they were different model years, but the different pole pieces puzzles me. I would not be surprised if the "6M15" unit had been played with, I am pretty sure the "8E16" unit had not.

Sorry for any confusion, PHAT!

Thanks!

Chris

You can put a single diaphragm vacuum advance on any dual diaphragm distributor.....but remember when they changed to the single diaphragm unit they also changed the camshaft as a set.  Maybe little known fact...but the combination of two is what got them past emission requirements.  The mechanical section of the 1111987 Type 1 (Dual Diaphragm) and 1111948 Type 2 (Single Diaphragm) are different.

401MATCOUPE wrote: You can put a single diaphragm vacuum advance on any dual diaphragm distributor.....but remember when they changed to the single diaphragm unit they also changed the camshaft as a set.  Maybe little known fact...but the combination of two is what got them past emission requirements.  The mechanical section of the 1111987 Type 1 (Dual Diaphragm) and 1111948 Type 2 (Single Diaphragm) are different. The 1111987 Mechanical Advance Specs are at 900 Engine RPM = 0-4 degrees advance, 1500 Engine RPM = 12-16 degrees advance. The 1111948 Mechanical Advance  Specs are at 800 Engine RPM = 0-2.5 degrees advance, 1600 Engine RPM = 17-21 degrees advance This tells me the main shaft cam and weights have different profiles. One additional note is a Type 1 set up the factory recommendations were 5 degrees +/- 1 BTDC (vacuum hose disconnected) and 34 degrees +/- 3.5 degrees Maximum Advance at 2000 RPM (vacuum hose connected). Type 2 set up the factory recommendations were TDC +/_1 degree (vacuum hose disconnected) and 45 degrees +/- 4 degrees Maximum Advance at 2000 RPM (Vacuum Hose Connected). That is a big difference, it is due to the combined additional mechanical advance and vacuum advance differences in each unit.  You can get very close using your 1111987 distributor by using an adjustable vacuum advance that Mr Gasket Brand (Summit sells) and small changes to the weights/springs. Vacuum advance spec for Dual Diaphragm Unit is Max advance is 17-19 degrees, proper single diaphragm is 24 degrees.

toolmanxiii wrote: 401MATCOUPE wrote: You can put a single diaphragm vacuum advance on any dual diaphragm distributor.....but remember when they changed to the single diaphragm unit they also changed the camshaft as a set.  Maybe little known fact...but the combination of two is what got them past emission requirements.  The mechanical section of the 1111987 Type 1 (Dual Diaphragm) and 1111948 Type 2 (Single Diaphragm) are different. The 1111987 Mechanical Advance Specs are at 900 Engine RPM = 0-4 degrees advance, 1500 Engine RPM = 12-16 degrees advance. The 1111948 Mechanical Advance  Specs are at 800 Engine RPM = 0-2.5 degrees advance, 1600 Engine RPM = 17-21 degrees advance This tells me the main shaft cam and weights have different profiles. One additional note is a Type 1 set up the factory recommendations were 5 degrees +/- 1 BTDC (vacuum hose disconnected) and 34 degrees +/- 3.5 degrees Maximum Advance at 2000 RPM (vacuum hose connected). Type 2 set up the factory recommendations were TDC +/_1 degree (vacuum hose disconnected) and 45 degrees +/- 4 degrees Maximum Advance at 2000 RPM (Vacuum Hose Connected). That is a big difference, it is due to the combined additional mechanical advance and vacuum advance differences in each unit.  You can get very close using your 1111987 distributor by using an adjustable vacuum advance that Mr Gasket Brand (Summit sells) and small changes to the weights/springs. Vacuum advance spec for Dual Diaphragm Unit is Max advance is 17-19 degrees, proper single diaphragm is 24 degrees. I'm confused now ..my dual vacuum advance dizzy has no mechanical advance . but uses manifold and ported vacuum to advance timing .

I tend to agree with 401MatCoupe, your PrestoLite Dizzy also has Mechanical Advance weights and Springs, they are just hidden buried down deeper in the distributor housing in those kind than they are in the Delco type distributors that have the mechanical advance right there on top right under the rotor button.