Just curious, but when did ventilated points come out?

I notice new, foreign-made replacements sold for my '55 have the vent holes, but the high quality, US-made NOS ones I sometimes get do not. Are the vents enough of an improvement to risk poorer quality control? You would think the missing metal would SHORTEN point life, especially in a positive ground system, where points last longer anyway.



Also, does anyone know if converting to dual points, can you safely increase dwell time using the stock coil without shortening it's life? What's the limit?

6 VOLTS/POS. GRD. NW INDIANA

g'day daniel

the supposed theory for ventilated points was compared to full face they had less surface area to arc & pit on opening & breaking the circuit.

moz. geelong victoria australia.

graduate 1980, bus, truck, car, hot rod, boat, submarine, hovercraft, hydrafoil, firetruck, mobile home, jet, helicopter, cruise ship, motorcycle, bicycle, santa's sleigh, clock, alloy bullbar, alloy fuel tank, lens, dr who's tardis, matter - anti matter warp drive buffer & y-block lover

I used the ‘Niehoff’ brand in the early days because they were vented.  Point life was excellent and would have to say it was better than using the non-vented points at the time.  The material being used on the point faces could have been the difference though but as Pete mentions, there is less surface for a buildup or pitting to occur.

 

As far as increasing the dwell time by going with dual points and using the stock coil, the 406’s and 427’s did this without any serious detriments to the coil life.  I ran many a dual point back in the early days without any coil issues and just didn’t give it any additional thought back then.

Lorena, Texas (South of Waco)

According to the first information I picked up, the dwell setting for the Y single point is 26°-28° and a representative Ford dual-point is something like 30°-33°. This last could be misinformation.......

Anyway, for one distributor rotation:

8 x 33° ÷ 360° = 73% duty cycle (dual point)

8 x 28° ÷ 360° = 62% duty cycle (single)

Not a lot of change in coil "on" time (duty cycle) - but the available spark energy to fire the plug (volt/amp/mili-seconds) as the rpm is increased, goes up by 18%. If the conventional system is on the edge of misfire at 4500 rpm - the dual point reaches that point at 5300. Other factors may drop this a bit - but it's the reason that dual point distributors were once the "hot set-up".......

 
 Steve Metzger       Tucson, Arizona