twin plug / brand new distributor or original modification

[florent78]

Hi guys,

I will twin plug my engine .... I know many many post on the forum about twin plug

I've got 2 questions regarding the possibilities.

1- I can buy a Patrick motorsport distributor so ...
The distributor is configured with a centrifugal advance of 8 degrees
this allows the initial setting of 20 degrees static
and thus a total of 28 degrees total timing is achieved at just over 2,000 rpm

2- I can ask to modified my distributor to twin plug it and this is the answer from the company:
Our distributor is a modified SC unit, unlike the Patrick Motorsport Billet item
which retains the original 8 deg of internal advance
giving a total of 16 deg of advance when fitted

so if I use MSD ignition module, the new distributor will gives better results cause you can have more advance.

NOW regarding MSD programmable ignition module
it means I will lock advance with my modified SC original distributor
so I can set an advance curve to get the same kind of advance Patrick Motorsport gives if I want

Is it correct ??

if so I prefer this solution.


My second question is for the MSD ignition module.

I know it's better to get 2 MSD ignition module to avoid to split signal between the 2 coils resulting in less spark intensity.


if I use 2 MSD ignition module.

do I need 2 programmable module as they are working in the same way.

or I can use 1 programmable ignition module
1 classical ignition module

the programmable ignition module will work as a master
an the non programmable ignition module will work as a slave


I hope I explain clearly my questions.

thanks for your help

[Mark Henry]

You are kind of confused on how a MSD programmable box works, advance curve of the dizzy doesn't matter because you lock it out.
Advance and spark is controlled/triggered by the MSD software that you program.
BTW you have to lock out the advance or the dizzy will be fighting the program.

The pick-up is also just a reference/sync point.
I would imagine you rough set the timing so that the contact is seen by the program, set the programed timing at ten degrees, start the engine and with a strobe rotate the dizzy fine tuning to ten degrees.
Once you achieve that you clamp the dizzy and never manually adjust the timing ever again.
You may not even have to fine tune the dizzy, you may just adjust the program. This is how it's done with the crankfire on my '67 bug with SDS EFI. On SDS the trigger can be as much as +/- 40 degrees out of the actual firing event.

I do know you can't use a programmable MSD on a stock 911 cap and rotor locked out, the legs are just not long enough. The cap/rotor contact area has to be as large as the advance curve on a locked out dizzy.

The Patrick (Jarvis) unit uses a MSD trigger, it's what I have with a single 6al box and twin coils, but I still haven't fired up the engine yet.

I don't know how you are modifying the the stock dizzy, so how can I/we give you an opinion. Would need more info.

[Jonny H]

If you used our CDI+ unit, you can lock the standard SC distrbutor with our locking device without even taking it out of the engine and get a fully programmable ignition curve. It will also (unlike MSD) give you true multispark to 10000 RPM. You'll also get soft and hard programmable rev limiters, a shift light output, free firmware upgrades for life and first class support.

[florent78]

after waiting answers from MSD and ..... nothing


I choose the clewett ignition distributor less solution

seems to be really nice to tune
and cheaper regarding twinplug distributor with coil and 2 MSD programmable


will tell you when I receive the kit

[snbush67]

Originally Posted by Mark Henry

I do know you can't use a programmable MSD on a stock 911 cap and rotor locked out, the legs are just not long enough. The cap/rotor contact area has to be as large as the advance curve on a locked out dizzy.

I am using a programmable MSD on a stock 911 cap and rotor locked out. It works great no issues.

[pkabush]

There are several 930s running MSDs with locked dizzys as well.

[Mark Henry]

Ok I stand corrected. Did it take you awhile to get the phasing correct?
SC and 930 doesn't surprise me too much as the later years the cap and rotor are bigger giving more wiggle room for the advance curve.
How did you find the MSD software?

[snbush67]

MSD software was simple and effective. No issues. I guessed on the phasing and I think I got lucky, there is a video in my thread which shows the spark. The spark starts out off center during low RPMs and moves dead center at max.

MSD 6AL-2 Digital Programable Install and Distributor Lockout

[Jonny H]

Originally Posted by snbush67

The spark starts out off center during low RPMs and moves dead center at max?

I can confirm that too. We have run modified caps so you can see the rotor in relation to the post. You will find that only half of the rotor arm shows wear over time but that isn't a big deal.

We offer a unique locking device for the SC/Turbo which can be fitted in minutes without taking the distributor out of the car. There's a picture of it on page 29 of our technical manual on the CDI+ pages here:

Bosch CDI replacement and classic car fuse panels

[chris_seven]

When using Twin Plugs with a Bosch or Marelli cap the rotor arm its design can also help to make sure that there isn't an issue with phasing.

As Florent78 isn't using a dizzy it shouldn't matter but using a rotor with the correct contact length is relevant.

The weight of the rotor and the potential for it to introduce 'swash' is important and having a bearing to support for the rotor helps.



When you convert the dizzy to twin Plug locking the advance is easily achieved.