<VV> Re: Dual Points-advantages?

[Tony Underwood]

At 12:31 hours 02/13/2006, Chris & Bill Strickland wrote:
>Boy!  it is simply amazing how much info people have forgotten over 
>the years -- as we move further into the age of electronics
>
>the classic dual point distributor was a rather successful attempt 
>to increase coil saturation at high rpm on multi-cylinder 
>engines.  the second set of points (when the lobe number matches the 
>cylinder number) can be adjusted to close much sooner than is 
>possible with single points -- cutting the dwell by maybe 40% 
>without the excessive point arcing you would find trying to do this 
>in a single point set up.  less "dwell" yields more time with the 
>points closed, which means greater coil saturation, which means 
>greater spark energy -- important stuff for an eight cylinder engine 
>at 8,000+ rpm in the 1960's.
>
>yes, it is an obsolete technology, but so are carburetors.  big deal.
>more important would be the lack of that fuel economy device, the 
>vacuum advance, on most of these units.


Not if you were a Mopar fan and your dual point was a Prestolite with 
vacuum advance.


>one other thing many of these units make available is a port to 
>drive a mechanical tach -- very retro, sorta like those carbs 
>previously mentioned ...   :)


I see somebody was a GM/Corvette fan.   They had tach drives on some 
distributors, but no Mopars I know of offered a tach drive on 
anything including the dual point distributors which Mopar actually 
didn't make (see Prestolite reference).


They did improve spark in the performance engines, although it seemed 
more along the lines of increasing coil saturation for purpose of 
making a more intense spark, not necessarily making a better spark at 
very high rpm since the 426  and 440 engines in street trim weren't 
high revvers although they did fill a cylinder pretty well and a 
dense mixture under high compression was hard to light off, thus the 
need for intense sparks...  not necessarily a high rpm spark 
capability.    Most bigblock Mopars would float valves at 6000 rpm 
*including* the Hemi (an intake valve that big is pretty heavy even 
with a 5/16 stem) but since they made most of their best power 
between 3000 and 5500 rpm anyway, it wasn't necessary to buzz 
anything any higher than that.

The logic was to make an engine produce its best work at a low enough 
rpm to remain together when pressed for its maximum output.   They 
wanted the engines to stay in one piece.     Thus, a 440x6 would make 
over 300 hp everywhere from 2800 rpm through 5600 where it was making 
almost 400 hp, in bone stock form.

No need for a dual point in any of those engines although you could 
get one if you wanted it by specifying the option.   However, the 
single point ignition on those engines was sufficient to allow them 
to do their worst damage to the dyno without misfiring.

It's old tech, admitted... and they weren't that much fun to keep 
right.   All they were was a temptation to overrev the engine 
IMHO.    Today I'd be going with the electronic ignition in any 
event, just because it's so easy to come by, rather than chase a dual 
point distributor that isn't so easy to find anymore.


In fact, my recent acquisition of another '66 Plymouth Satellite came 
with the offer of either the dual point or single point distributor 
for the bigblock engine in the car.

I picked the single point.   It's never gonna see more than 6000 rpm 
and I can find points for it anywhere.   Not so easy with the 
Prestolite.   Besides, what's to stop me from picking up an 
*excellent* stock Mopar electronic ignition setup for the car?




In 1968, with that high revving 302, 327, or 340 smallblock breaking 
up because of points issues, the dual point saved the day.

Not anymore.   If I want the musclecar to buzz tight, it will get 
electronic ignition.   Show cars with matching numbers need not 
apply; nobody drives them anyway.



tony..