Poor Mans twin plug

BBShriver · 03-16-2008, 05:25 PM

Here's what may just be a theoretical question on the twin plug setup.
Has anyone ever tried, or have any suggestions on using a 6 cyl distributor with some sort of "Y" harness to fire 2 plugs?

This would presumedly require some extra development in the coil/spark management... just curious.

jcge · 03-16-2008, 07:53 PM

My guess is that only one plug would actually fire - there will be a slight difference between the impedance to ground between the two plug gaps (no matter how well "matched"), and the energy will take the path of least resistance.

Even if you did match them exactly, and got both plugs to fire, the spark energy would be divided in half - it would struggle to fire a wet mixture.

Sorry to deflate your idea
Regards
John

Jeff Alton · 03-16-2008, 08:02 PM

IF you a 3.2 search out member "patton" and "twin plug". He built his own splitter that worked well and was inexpensive to put together.

You would still need a twinplug distributor, but those can be found for reasonable money.

Cheers

HawgRyder · HawgRyder's Garage

Electricity takes the path of "least" resistance.
So...if one plug is lower resistance than the other...only one fires.
However....if you were to "split" the power using a Balun transformer....they should both fire.
And with plugs...it's not the current...it's the voltage that makes the spark.
But....as compression goes up...it takes more current to jump the gap.
Bob

JohnJL · 03-17-2008, 09:47 PM

Hi Jeff,
What do you consider "reasonable money" for a twin-plug distributor? I'll tell you what I spent after you tell me!

J

cfc · 03-18-2008, 04:40 AM

I had a Zundapp motorcycle in the 50's with 2 plugs, one coil, and a Y harness. Both plugs fired.

HawgRyder · HawgRyder's Garage

You got me to thinking (a bad thing)...
Years ago, I saw an ignition system that was basically a coil on plug system.
It had a low voltage distributer with wires running to separate coils on top of the engine (straight 6 if I remember right).
The system was simple, but I did not get ot see inside the distributer, so I don't know how the rotary gimick worked.
But from a tech standpoint, it would be cheaper than re-wiring the whole engine for a sensor-on-tooth system.
Perhaps someone else can shed some light on this old piece of interest.
bob

Jeff Alton · 03-18-2008, 07:46 AM

Quote:

Originally Posted by JohnJL

Hi Jeff,
What do you consider "reasonable money" for a twin-plug distributor? I'll tell you what I spent after you tell me!

J

I have sold a couple in the last 2 years for 275 each... (964 ones)

Cheers

afterburn 549 · 03-18-2008, 07:54 AM

My only Q.
Why twin plug ? (Oh I know why, But you need a reason beyond a stock configuration ) So for you to benefit from T.plug. .. you must be other then stock ??? so now you are in a big quagmire, you need more timing, less timing ECT.
So if you are high rev carb, high C/R or turbo, to benefit your stock timing curv esp. for turbo will never work..........so a 1400 to 1600 dollar system like XDI or SDS seems to be simpler as it will not only give you twin plug, but infinite time curve

JohnJL · 03-18-2008, 01:18 PM

Not sure if that ? was for me, but if so I have 11:1 compression.

Jeff, you just ruined my day. ;-)

BBShriver · 03-18-2008, 01:43 PM

My 73 was bought to make an SVRA racer... Since the class limit is 2.5L and twin plugs are allowed... y not?
The rule still requires distributor driven though.

afterburn 549 · 03-18-2008, 04:01 PM

For the thread starter..twin plug will not do much for a stock eng. And if it is not stock.....timing can be the next big issue even if you have a twin plug set up

Jeff Alton · 03-18-2008, 04:27 PM

John,

You will have right of first refusal the next time I have a 964/993 distributor for sale!

Cheers

BBShriver · 03-18-2008, 05:37 PM

When we get around to rebuilding the engine, it will/should be full race spec. The limits the way I read them dictate displacement, but not cams, or CR, and twin plugs are allowed... So it seems twin plug would make sense in that application (as evidenced by every other race spec 911 I've seen having twin plugs)

jcge · 03-19-2008, 02:02 PM

Quote:

Originally Posted by mike curnow

2 plugs, one coil, and a Y harness. Both plugs fired.

I'm happy to stand corrected

Regards
John

safe · safe's Garage

Quote:

Originally Posted by mike curnow

I had a Zundapp motorcycle in the 50's with 2 plugs, one coil, and a Y harness. Both plugs fired.

To the same cylinder?

cfc · 03-21-2008, 06:53 AM

Quote:

Originally Posted by safe

To the same cylinder?

Yes, the Zundapp was a single cylinder cycle, 250 or 350cc with one coil, a Y plug wire to the 2 plugs, and a cylinder head with 2 plug holes, all factory.

911st · 03-22-2008, 03:19 PM

I heard one unique solution to twin plug from before electronic twin plug systems and second had C2 distributors.

It was to drive a second distributor off the back of the camshaft like a MFI pump or C2 power steering. The main distributor's points were used to triger both coil systems. Does not have to be a Porsche unit but would probably need and advance set up to keep the rotor lined up but not sure.

Do not seeing anyone doing this.

One of the shops I went to was trying to put an advance and triger from an SC in one of the C2 style twin plug distributors as they do not have points or other triger. Not sure but the rotations might be different.

Low compression motors can actually benifit from twin plug also but the gain is not usally worth the money or effort.

The first benifit is for motors that can run rich like race carbs or MFI as it helps to ensure combustion and reduce missfire.

A Turbo with CIS is a good example that can benifit. It dose not need twin plugging on boost as the A/F mix is very volital and burns fast when lit anyway. Which is why they retard ignition on boost.

But, 930's are often run rich for several reasions. A Twin plug system helps ensure it will light the hard to fire mix.

It also can add a little bit to off boost torque and throtle response, even with the low 8.5 to one.

Twin plug systems are timed with less advance than single plug. This is because it burns the mix faster with two flame fronts. With the later ignition

the motor can get closer to TDC before ignition is started for the power stroke. Think about it. If the fuel mix is lit at 24 deg before TDC instead of 32 deg, less pressure it being built in the combusion chamger on the way up for the power stroke.

Thus, less presure on the way up and the same on the way down = more total power.

As to the two plug one wire thing. I suspect that one plug with the least resistance would fire tell for some reasion the other plug was the path of least resistance. Two strokes liked to foul plugs so it might have inproved odds of at least one working????

My $.02.