Ignition choices for 3.6 w/ PMO's
 

OK Guys, what is the best ignition system for a 964 3.6 with PMO's that will be landing in an SC. Motronic is gone.

The engine has the 964 twin plug distributor with 930 internals. I am concerned with this set-up. No provision for initial timing adjustment and hit and miss for a good advance curve.

2. Electromotive XDi twin plug set-up looks easiest and most tunable, but I have read that this may not be the best for idle-rich carbed engines.

3. Twin plug 12 cap dizzy with MSD's. - Are the new rotors holding up?

BTW, this is Taso's engine that Scotitude listed here about a month ago. It is going in my friends 82 SC. http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/260711-fs-964-3-6-a.html?highlight=3.6

Any words from experience?
Thanks, Lyn

I am faced with the same dilema for my carbed 3.4..... I have a twin plug HPV-1 set up on the shelf, just not sure that I am going to use it.

Cheers

I have heard many differeing stories as to the quality of electromotive parts. Almost went with the kit that Clewett sells but its high cost versus chance of failure versus better options for less led me elsewhere. A dizzy that can fire 12 plugs with two MSD boxes and coils works fine. You can buy a box from msd that allows you to advance and retard the ignition timing. Thats probably the easiest route since you have the dizzy.

Those twin plug caps look great but what happens when you cant get the custom rotors anymore? For many the factory twin plug is financially prohibiting so its nice to see this being made but at the end of the day I will end up spending less than a custom MFI setup with twin plug dizzy and all those old school racey goodies and have more flexibility and support. I have great respect for what was done but unless your a super anal concours whacko using the expensive porsche stuff is silly when you can get EFI on the cheap these days and its getting cheaper.

FWIW sell your carbs, sell the electromotive, sell your dizzy, go buy some TWM to use with your weber manifold or Jenveys, an aftermarket ECU and coilpacks and sensors and call it a day.

Lyn:

Personally, I'd never use an Electromotive setup on a carbureted engine ever again. They cannot keep the plugs clean if it idles for long and they will not support the wide plug gaps that make more power.

You have several options.

1) Use the 3.6 dual-dizzy and either modify it for adjustable advance or use an MSD adjustable timing controller. It must have a trigger installed inside to trigger the MSD boxes.

2) Install one of the newer RSR type distributors that use the Jaguar Marelli cap and custom rotor. There are two manufacturers of those things and both are really very nicely done.

MSD's (properly installed & setup) really make carbureted and MFI-equipped cars run exceptionally well,......:) EFI with the right intake and Engine Management system is the best without question, but that cannot be done well on-the-cheap.

hope i can piggyback onto this thread:

this is exactly why I'm trying to avoid running twin plug on a new-to-me 3.2ss- too many unknowns, hassles, and expenses.

does anyone know approximately what i will be sacrificing by going w/ 9.5:1 instead of 10.5:1 in order to stay single plug? (i know this is cam dependent, along w/ a host of other variables, but let's say it's a modS cam w/ webber 40's....)

Dave, I am sure Steve is theh expert here but...

I suspect it might have to do with a few things that are internal to the engine. what pistons? If they are the Mahle or JE wedged dome, the shape can effectively divide the combustion chamber. This causes a delayed flame front which can lead to detonation. Isn't this what happens with the high compression 2.0 setups? for comparison of shape only , IIRC the 3.6 piston is fairly flat on top.

I think the compression ratio can be raised slightly with high-overlap cams. Its all about the difference between dynamic and static compression ratios. the ModS cam can be ground with different lob centers. Moving from 103 to 108 would cause a big difference in dynamic compression (and probably low end torque vs high rpm HP).

I think that ModS, 98mm 9.5:1 pistons and carbs you would be fine with single plug. I suspect the motor would run a little crisper with twin plug.

I was under the impression that using either the twin dizzy or the 12 plug RSR type dizzy, dual MSD boxes (or other controller) produced a better spark?

I understand there is a MSD box that will allow you to program a timing curve. Anyone know which ones will allow you to do that? Could you use them to fire a 964/993 twin distributor?

Thanks

I thought it was an atachment to the 6AL

http://www.msdignition.com/pdf/6%20series/pdf5.pdf
this shows a timing box hooked up to a 6AL

EFI cant be done on the cheap? How much do a set of new PMO's cost? Then add in either custom 12 plug dizzy, rotor, cap, two MSD's, coils and you are pretty close. Go with the 964/993 dizzy and put in some older dizzy guts or get an MSD box that will allow you to adjust timing. Or the electromotive system which isnt cheap either.

TWM, Jenvey, slide valves, they can range from less than 2k for a used set to however much you want to spend for custom slide valves with carbon trumpets. FWIW I have seen Jenvey TB's advertised for 2700 with fuel rails, TPS, manifold, linkage, air horns, filter baseplate and filters. Then spend about 2k for a brain with wiring harness, software, buy some bosch coilpacks, get your O2 sensor, MAP sensor, air temp sensor, second set of plug wires and have at it. If you really really really were all about DIY and custom work you could buy all this used but I would get new sensors and coils. I am sure if you were patient and knew what to get you could set yourself up with EFI/ITB's for about 4k.

Hi Jeff:

There are several MSD products that will do this job and all vary by advance/retard resolution and control.

Look at the: #8981; #8983, and #8975 timing controls.

These are all designed for the 6-series of ignitions that can be triggered with the 3.6 distributor provided its been modified by the installation of an SC magnetic trigger.

Jeff,
You can use 2 4channel MSD digital boxes with your Electromotive set up, that way you can gap those plugs, I have done it a few times, it works without a hitch.,cheers,Antonio.

Antonio, can you explain how to wire this and which MSD boxes excactly?

Thanks

Jeff,
Go to Msdignition.com, download the instructions for DIS-4 Multi Channel Ignition, part #6215, you will need 2 of them, it is a straight foward install, If you have problems pm me, cheers,Antonio.

Thanks

Thanks for everyone's posts! This is exactly the discussion I wanted to hear to my original question.

Since I have a 964 distributor with magnetic pick-up installed, I am leaning toward the MSD 8981 that Steve suggested to control the advance curve. The mechanical advance in the distributor must be locked to let the 8981 control the advance.
When locked, will the rotor and cap posts be close enough to jump a 28 degree advance that the controller/coil are sending back through the high voltage path?
Thanks
Lyn

I'm currently running the Eletromotive HPV-1 on my 3.4 twin plug w/46mm webers. I'm confused. Where does the MSD tie into the HPV coils?
Harold
'75 Carrera RS (look)

Hi Lyn:

You are asking about two different issues here;(1) rotor phasing where the magnetic pickup is positioned to match the timing of the rotor/cap posts and; (2) ignition advance where the spark occurs relative to crankshaft position.

If the magnetic pickup has been installed & positioned correctly, rotor phasing is retained. This is usually done by checking the distributor on a special machine made for this.

Igniton advance can be done by either utilizing the advance mechanism inside the 3.6 distributor or by locking it in place at full advance and then using the MSD timing controller to provide the starting retard and various levels of retard at specific RPM points.

Thanks Steve!