Ignition info required:

[911hillclimber]

Does anyone have any tech info on converting/making a twin plug distributor for the 911 engine?
I have one in front of me on loan.
The hard bit is the sensing of the rotor arm position, rest is simple machining.

There seems to be quite an outbreak of whole distributors available in the USA and the Bosche distributor cap and rotor arm are now economically available. Such distributors are about $2000 so £2000 landed. I fancy making one.

I am particularly interested in the sensing of the 12 plugs/rotation and hope to use a hall effect transducer.

However, any DIY info from whatever period would be interesting at this stage.

[Lightweight_911]

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If you go back ~ 15 years there were several people in the USA doing this type of conversion - eg Andial, Steve Weiner (Rennsport Systems), Aaron Burns (Burn Bros), etc.

I've had a number of these (all of the above early examples plus others) - if you do a search on Pelican you'll find lots of threads on the subject.

Due to the rarity/cost of original Bosch & Marelli twin-plug caps most of the conversions back then (except Andial who used original Bosch caps) used Jaguar V12 caps.

Here's a typical early thread on Pelican:

http://forums.pelicanparts.com/porsche- ... ekend.html

I used one of Aaron Burns' later twin-plug distributors (sold via Henry Schmidt of Supertec) in my 904 & once fitted/set-up it was completely reliable & fault free.

I had 100's of pictures of original & repro twin-plug distributors but most were lost last year when an external hard drive was irreparably damaged ...

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[911hillclimber]

Thank you v much Andy for this info.
I see this as possibly Plan B or C to my Clewett recovery if their XDi fails to work.
I have the distributor off the engine, the Bosch 6 plug converted to hall effect, works a treat.

If I machine a simple top hat to hold the rotor cap at the right height from the engine mounting base lug on the dist and machine the rotor arm to align to the cap the current sensor will time the top plug of cylinder #1 to fire from Coil #1.
Simultaneously, the second finger on the two contact rotor arm will be on another pole in the cap and then coil #2 can discharge to the lower plug on cylinder #1

Next pole round will be discharged etc.

The cheapest i've seen today for a dist cap is £200 and a rotor arm 48. I think these are not V12 Jag as the cap has twin coil input. Could be wrong.

The unit i have on loan is made by Adapted Products with Bosch ignition units and twin coils.

[Lightweight_911]

The cheapest i've seen today for a dist cap is £200 and a rotor arm 48. I think these are not V12 Jag as the cap has twin coil input. Could be wrong.

The simplest was to distinguish a Jaguar XJS V12 Marelli cap from a Porsche 911 Marelli twin-plug cap is by the 2 coil terminal posts - on the Jag version they're different heights:




- whereas on the Porsche version they're the same height:





Incidentally, there are also old threads here on DDK on the subject of distributor conversions - eg:

https://www.ddk-online.com/phpBB2/viewt ... +twin+plug


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[911hillclimber]

Most helpful Andy.
I fancy doing this just to see if I can.

[911hillclimber]

Slept on this and read the link DDK link Andy posted.
Interesting that Chris at Fenn Lane was touching on the subject way back.

I hope there are some techies reading this.

The system I have on loan is a hall sensor to trigger the engine timing position just like any normal simple distributor.
The rotor arm has 2 fingers, both allow the coil)s) to discharge to a given cylinder plug 1 and Plug 2 simultaneously.

There are 2 Bosch 'black boxes' # 0 227 100 137 that you can by new off ebay (!) but I don't know what they are but they need a heavy heat sink.
These 2 boxes link to the ordinary looking 12v coils, no more, no less.

So, why can't I use my old distributor, convert the cap to a 12 plug cap, correct rotor 2 finger rotor arm and two simple coils?
Why do kits in the USA (ie Patrick Motorsport) come with MSN red box?

Is my simple layout too simple to be effective?

[Nine One One]

http://www.autocomponenti.com/performan ... wiring.htm


I think if you do a read up on the Alfa Romeo twin spark system you may find your answer?

[jwhillracer]

I'm pretty sure that Andy Haas (haasad) developed a twin plug distributor conversion a few years ago before he was diverted off into straight six Healeys.............

JW

[911hillclimber]

Yes Jonathan, that is the one on Andy's post above. Will have another read.

People fit the MSD unit so there will be a reason, but this is just a doubling up of the 6 plug system i had, and a coil worked fine.

[Jonny Hart]

The two Bosch ‘boxes’ are TCI ignition amplifiers. A TCI system requires a TCI coil - not any old coil. It bugs me that people see a round canister with 3 leads and assume they are all the same. A bit like me saying all con rods are the same.

There is a certain 917 of some fame (perhaps THE famous) that has never quite run right in 20 years. It’s had numerous engine rebuilds, Bosch pumps, tune ups and roll roads - literally millions spent on it. I had the whole ignition system here for analysis. Everyone thought it was cool the way it pops and bangs in the paddock - proper race car. Er, no - it had the wrong coils! With the correct spec coils it is now running correctly and can actually be raced rather than a paddock ornament.

[911hillclimber]

The coils in the loaned system have black tops and a red dot designed into the top moulding.

One this subject, does a twin plug need the other parts to work?

[Jonny Hart]

Not much to go on with the coil - you need to know the spec.

I think you already know my suggested best ignition route for a twin plug.