Twin vs Single Distributor

Dual distributors for USA delivered 308s due to smog emissions testing. Each distributor needed an additional set of points in each distributor to retard the other points in the distributor when at idle via a switch activated by the throttle linkages / carb. Smog reasons only.
This is why I will be modifying my rear bank distributor to fire both rear and front bank spark plugs and have the single advance curve.

 

No single distributor US 308GTB carb from the factory -- all have dual distributor (not so easy to put 4 sets of points into a single distributor).

I believe all euro 308GTB carb are single distributor (early using 2 sets of points, later using a dual electronic ignition).

I think everything 308GTB injected (whether US or euro) uses dual distributors (but they are a lot more simple thing).

What is the basis of your question?

 

Not aware of any switch to single at least in US. Dual is just the Ferrari way, two of everything, except when it comes to mufflers then maybe eight.

 

It's usually about spark energy and time. Its just plain hard to get a coil to full charge in the dwell time available on a high rpm V8.....dual gives double the time and generally a hotter spark as a result but the adds a bit of weight which I suspect is why some euro car had single.

 

My 1976 built gt4 UK market has a single distributor. The single distributor uses two coils and two separate charging circuits so I don't think that's the reason.

 

On USA emissions cars the second set of points were operated by a micro switch. At idle the engine ran on retarded timing points. When the engine was accelerated it winched to the run set of points. The cars had two coils so, coil saturation was not a problem like with a v8 with a single coil.
This system was probably used raise exhaust gas temperature for emissions.

Sent from my SM-G950U using Tapatalk

 

I don't think we're talking about dual points, the OP means dual distributors (one per bank) vs a single 8 terminal distributor for both.

 

Well the "when" was "always" 1976 onward.....as discussed above the North American cars "needed it" to pass DOT emissions.

Euros ran thru 1980 with carbs and a single unit and NON CAT.

The "why" was totally legal, to meet various market demands, just like adding CATS.
I don't think Euros got CATS untill 1984??

 

I've been sidetracked for 10 years with my dad's 74 911 restomod.
I had my 77 ignition upgraded from dual point, dual distributors to a single 8 cylinder configuration. This involved a modified ford rotor, a chrysler magnetic pick up and a shameless chevy 260 v8 cap. ( the distributor body was turned down a bit to fit the $20 chevy cap). With a recurved advance and the addition of an MSD 6AL and a "blaster" msd coil, I now have an easily and cheaply maintained, long life ignition. No more worn out rubbing blocks/points, no synchronizing issues.
Looks stock, except for the red blaster coil. the msd is in the left trunk well.
I'm having a senior moment, forgot the name of the business that does it, Norwood Motors???

Finallly getting back to the 308 - about time for a major. Might go to Forza's trick adjustable cam timing pulleys and long life belts - yet another way to minimize the high maintenance costs of 308 ownership.
chris