Twin plug ignition???

[YTNUKLR]

For twin-plugging an engine: what are the options, how much do they cost, and what do I have to modify on my car to utilize each one? What are the pros and cons of each system? Hypothetical engine might either be a 2.8 or 3.5, 911S cams, Weber 40 and 46, respectively...Thanks!

[afterburn 549]

well ,,,
you have landed in the t.m.o. zone here is mine.....if your heads are off drill them for twin plug in case you lose your mind later and want to go there later.
2 there are all kinds of ways to get there some rather crudish some rather exotic.
3 I like s.d.s as you do not have to run to a dyno and run a around with a lap top and for the same cost almost as other systems you can go to efi.
thats my O.- you do not have to agree with it and not tring to start what is best war......just what I like for me

[emcon5]

There are 3 basic ways of converting a single ignition 911 to twin ignition, with a distributor, with an electronic crank-fired setup, or a combination of both.

Distributor : There are 3 options,

1: Find a used twin plug distributor. These come for sale from time to time, but are very expensive. They come in both RSR and 935 versions, don't buy a 935 distributor, as they have no mechanical advance, and would only run well at high RPM. I saw a 935 distributor for sale at a recent swap meet for $2000 with cap/rotor/wires. The seller reported it had been installed on a N/A MFI 2.8L race engine, and it ran good, but was really hard to start.

2: Convert a single plug distributor to take a 12 point cap and rotor. Andial does this conversion, it is also expensive, and the Bosch cap and rotor are VERY expensive ($1000+).

3: Convert a 964 dual distributor. Rennsport does this, as do a few others. I don't know about the others, but Steve Weiner at Rennsport installs the trigger from a SC distributor, and uses standard 964 tune-up parts. It will not fit on a turbo engine. I saw a 964 distributor with wires at a swap meet recently for $250, and the conversion is ~$400 IIRC.

All distributor options need a second CDI unit and coil, and the necessary wiring. Depending on which engine, and which distributor you are using, you may need to change the distributor drive gear on the crank, to make sure it spins the correct way.

Crank fired : Electronic twin plug solutions can be anything from full engine management systems, to the more economical Electromotive. There are a number of crank fired ignition systems from companies that have traditionally catered to the domestic Hot Rod market that can probably be adapted to a flat 6, like MSD, or Accel. There are also a number of crank fired ignitions on existing cars that may be adaptable by a resourceful do-it-yourselfer. An off-the-shelf electromotive unit costs ~$1600, Junkyard solutions will be less of course, but you will be on your own.

Combination units: This primarily applies to 84-89 3.2L engines, which use a electronic ignition with a distributor. On these engines, all the timing advance is controlled by the DME, rather than in the distributor. The 964 uses a similar system but with twin plugs. Andial makes a splitter to convert the stock DME output to drive 2 coils and a stock 964 distributor. It may also be possible to use a off the shelf timing control box, like the MSD Programmable Timing Computer to drive a 964 distributor on a non DME car, but like the junkyard crankfired solutions, you would be largely on your own.

In all cases, you will need to have the heads machined to add the lower spark plug holes. You will need to modify the lower valve covers to route the plug wires through, as well as the right side chain box to make room for the # 4 lower plug wire. This should add ~$400 to a standard top-end job machine work.

You will need to modify the engine tin to route plug wires. You will need to change one head nut on the bottom of each cylinder, the barrel nuts are too fat and prevent the plug wrench from fitting over the plug. You may need to modify the heater ducting on the left side to clear the new fatter distributor.

If I am overlooking something, speak up.

Tom

[afterburn 549]

Nope,,..Ithink you covered it very nice.....imo i would look at some kind of a stand alone sys rather then a dist. set up. For the $$ they are both expsive but the stand alone you can pretty much make it do what you want.

[Henry Schmidt]

I know this is not applicable but I thought you guys would get a kick out of it.
This has a 962 part number but I'm not certain what it ran on. It bolts to the back of a cam tower and drives off the cam.
It works by running a standard distributor and two CDs. The standard dist. supplies the signal and this dist. just distributes spark.
The base of this dist. is a turbo scavenge pump so it serves two purposes.
Pretty cool ?

[Grady Clay]

Tom,
Great summery.


Henry,
I did the same thing in the mid ‘70s, sans oil pump. It was driven off the MFI cam. It used two machined parts and a stock rotor (rev-limit or not) and cap, less than $100. The cap was similar to the 962 one you show, screw down with a rubber gasket (not a Porsche part at the time.) It required 90 degree wire connectors to clear the stock heat exchanger or race headers.

Note the long arc of the rotor contact. Since there is no advance mechanism to keep the rotor aligned with the cap contact it is necessary to have that long arc and careful alignment to the cap. Note the long slots in the base.

Back then I used two Delta Mk 10 CDI ($50 each) designed to fire off one set of points in the original distributor (same set-up as we used on all the 4-cam Carreras.) We limited the range of the advance curve.
This also worked well with the 4-point Marelli C6 distributor where I could switch select different points for different total advance. Early DME.

With an “E” and an “S” rev-limiter rotors, it gave a great soft limit in the days before electronic limiters.

It all worked great. You have to know what to look for to tell that it is twin plug.

Best,
Grady

[Fishcop]

Wow.... hmmm, I've got a sporto oil pump kicking around here somewhere....

[Henry Schmidt]

Originally posted by Fishcop
Wow.... hmmm, I've got a sporto oil pump kicking around here somewhere....

Sporto pumps work great for transmission oil cooler and spray bar applications. Be careful to adjust the pressure, it way too high in stock configuration.
The dist cap and rotor don't have to be attached to a pump.

[BURN-BROS]

saw a 935 distributor for sale at a recent swap meet for $2000 with cap/rotor/wires.

So what is a realistic price for a marelli or bosch? 2000.00 doesn't sound too bad if it was the right one for the application. I have seen used Marellis for 3000.00 and an n.o.s. one for 6000.00.


BTW, I am about 2 weeks away from casting (prototyping)a rotor that will utilize the $60.00 Jaguar cap for the Marelli. I am just waiting for a few internal components. I will post pics if there is any interest.

[crash13]

Sorry to hijack this thread, but...

I'm looking at an early 911 with a twin plugged 2.8. The engine was built in the '80s and uses a distributor from a company called Levtech. I can't seem to find any information on this company. Does anyone have any information on this company or distributor (cap and/or rotor used?).

Thanks.

rob

[Steve@Rennsport]

Rob:

I think I know what that is but if you could send me a pic to help make a positive ID, I'd be happy to help.

[cstreit]

TimT forgot one.

ID BurnBros on this board is making a conversion kit with a Jaguar 12-point cap and rotor I think. May still be in development.

[Shuie]

Here's the link to Burn-Bros marelli cap & rotor project. Its a long read that has been posted many times, but its well worth re-reading and re-posting. Very cool project that worked out very well producing a product that will help a lot of us out.

Twin Plug Goodness...Look what I made this weekend!

[crash13]

Thanks for the reply. I have read through the threads on the BURN-BROS project. It amazes me what can be done by people in small shops and it may be the solution for this car. The owner has limited documentation on the distributor and the manufacturer, as far as I can tell, is no longer in business.

rob