Twin Plug Distributor Solutions

BURN-BROS · 09:22 AM

Here we go! Sorry about the wait as I have limited use to a camera. Early this year I manufactured a rotor for the Marelli twin plug distributor. For those that do not know, the Marelli twin plug distributor was fitted on all racing applications up until 1972. The venerable 906 as well as the 911R, 911 ST and 911 2.8 RSR all made a home for this high quality piece. A very robust unit, it utilized lower and upper sealed bearings for longevity. The only problem with it was that it had a tendency to bounce points at high rpm. FYI, this distributor should not be confused with the single plug unit found on the regular 911 !

The prices of the original cap and rotor for this distributor are extremely expensive. Old stock can command $700 dollars for the cap alone! Replica caps and rotors retail for $800.00 to $1,000.00 depending on the exchange rate and markup. Pic of the replica cap and rotor below. Notice the carbon brush on the rotor.

I decided to make my own rotor that works in conjunction with a much cheaper cap found in the mid 1990s Jaguar 12 cylinder car. The bolt pattern of the cap is identical with the original version but is a slightly different design. Both the Jag cap and my rotor are a direct bolt on for the picture above. Here is a pic of the jag cap and my rotor.

This substitution allows for a much lower operating cost and hopefully increased demand for entry level conversions.

Since a single plug distributor does not share the same dimensions as its twin plug brethren, you must convert it with adapters so that you can bolt on the cap and rotor. There are a number of solutions in regards to twin plugging your engine. The least costly is the conversion of a single plug unit (Bosch) that came standard on the 911 in the late seventies. These types of conversions are generally cheaper initially but may require more frequent service of the bushing.You can normally have a dizzy converted by an engine builder. Here is an example of a Bosch unit the expensive Bosch cap and rotor. It is from one our members in the classifieds a while back.

The 964/993 distributor can also be installed but will not work in a turbo application. If you are not concerned with aesthetics, this a fine route to go.

The mid level solution is a replica distributor. There is one out now and mine is on the way. These are purpose built and use the latest in pointless ignition systems.

The highest level is the original Marelli (see first pic) that varies in price from $2500.00 for one in fair condition to $6000.00 for an NOS example! Expect limited duty with the originals as these have 40 year old parts. The lower bearing as last I heard is special and in no longer available. Carl Thompson does have quite a bit of parts for them, but don’t expect a deal as they are exclusively priced (as they should be)…

There are distributorless ignition systems that are available and give the best is drivability, performance, etc, but I have focused on distributor type applications for obvious reasons.

This post is a work in progress and I am sure I am missing some aspects which I will add when notified of when I can think of them. Prices are not included as they vary from application to application. I am working out agreements with a few stores with Pelican being one of them. (edit)Feel free to P.M. me for purchasing caps and rotors untill then. P.M. me with conversion questions for you application.

Thanks guys!

mb911 · mb911's Garage

I was wondering the same.

Early_S_Man · 07-29-2005, 09:08 AM

The original Marrelli twin-plug racing distributor was pn# 911.602.029.00 ...

BURN-BROS · 07-29-2005, 09:33 AM

I started editing my original post. There are still some problems with a kit right now, Mainly dimensional variances in the distributor body itself. So only caps and rotors right now.
I am working with a few engine builders right now because they have the tools to make a very good conversion. I can get anyone who is interested in having a distributor converted in contact with knowledgable people to address their specific needs.

911SCfanatic · 911SCfanatic's Garage

Aaron, this is a ridulously sweet project. Sent you a pm.

Elombard · 07-29-2005, 11:07 AM

I want to convert my Sc dizzy to work with your Cap and rotor for $250. (including a new cap and rotor).

Guess I will be wiaitng a long time???

jpnovak · 07-29-2005, 11:21 AM

Sweet!!!

jpahemi · 07-29-2005, 05:22 PM

very nice.
j.p.

arrivederci · 08-02-2005, 07:39 AM

Very nice. I assume this would fit a twin-plugged 2.8 when all is said and done, right?

BURN-BROS · 08-02-2005, 06:03 PM

Thanks Guys,

These will fit with the appropriate adapters no problem. Especially a 2.8

gianpaolo911 · 02-09-2006, 05:17 AM

Quote:

Originally posted by Elombard
I want to convert my Sc dizzy to work with your Cap and rotor for $250. (including a new cap and rotor).

Guess I will be wiaitng a long time???

I try rotor reproduced for new cap
send for italy ?
Price for 3 rotores marelli ?
ciao zanetti

starlifter1 · 05-18-2006, 11:11 AM

Will the kit work on an SC dizzy without changing the rotation? as on the twin cap 964 dizzy. I do not want to break open the case to change the gear for the dizzy.

911SCfanatic · 911SCfanatic's Garage

you need a turbo dizzy to get the rotation you want. one was for sale recently in the 911 parts forum. search for it. I would have grabbed it, but already source an SC dizzy.

911 tweaks · 07-18-2006, 07:54 PM

I as many have read this thread from begining to end.

You have answered one of my main $$ questions which plays into how well I can spec the mods for my rebuild.

An update please on your parts, kits, $'s, availability...

keep up the great work & I hope it is working out ($$) for you!!
Bob

BURN-BROS · 07-19-2006, 07:47 PM

Hi Bob!

I have had great interest in Europe which I did not anticipate for. I am currently working on the second batch so I would say it has been a success, although not enough to do it full time

I have not solved the "issues"inherent to a kit. The dimensions are all over the place in regards to the stock dizzy. The builder of the Dizzy has to compensate for the differences with a lathe which makes it tough. So I worked with Henry(Supertec) to get the best priced converted unit we could muster without sacrificing quality. They came out looking very good...if I do say so myself

I am running out of my first run of rotors but I should have the others done in the next couple of months.

Be on the lookout for my Marelli replica distributor which I keep saying..."will be done anyday now"

I also have sump covers that I need to talk to Wayne about. Henry already has a few for current engines that are being built and will also sell them . PM me for a pic if you are curious! And the price is reasonable to boot!

It is very satisfying for me to make something and have the end user smile. To me that is the good stuff.

I do thank you for the kind words and I hope that 2006 has been kind to you.

Best!

Steve@Rennsport · 08:32 PM

Aaron:

That looks REALLY nice with the top of the rotor being supported with that bearing. Good job!

I've seen so many worn shaft bushings and out-of-balance rotors (Bosch & Marelli) tear up many expensive caps over the past 30 years so I'm very pleased with your efforts

I hope that your Marelli replica uses sealed ball bearings in 3 places with your design.

Have Blue · 07-20-2006, 08:51 PM

I had my standard distributor modified to take the RSR/935 Cap and Rotor. It's a tight fit on a turbo but it works well,and you can't beat that "race car" look!

pickupguy · 07-23-2006, 04:13 PM

Be careful guys....I have a Jaguar V12 with the Marelli ignition system. They are prone to failures I hope you have solved that problem. Just do a search for Marelli Failure on Jaglovers.com. What happens is one bank will stop fireing then the fuel flows in the cyl, out cyl into the cats and catches on fire soon engulfing that wonderful V12 in flames.

jdm61 · 07-23-2006, 04:25 PM

Is the jag issue a Marelli problem or can we lay it on the doorstep of the Prince of Darkness, Mr. Lucas? lol Oh....by the way........$6K for a DISTRIBUTOR? You guys truly are mad!!!!!!!!

BURN-BROS · 09-16-2006, 09:45 AM

Wow, missed some posts here.

Steve, Thanks for the kind words and I hope you are doing well...three bearings!......I'll look into it...

Pickupguy, I have studdied up on the phenominah. Jaguar was trying to run too much voltage thru their dizzy. Keep the voltage down to a "normal" (25,000 to 35,000 volts) range, gap your plugs accordingly and you will have no problem. Most of the manufacturers were moving away from the cap and rotor technology during the 90s to run higher voltage....Jaguar didn't follow suit which in the long run was good for us.

jdm61, You can indeed lay what the Jag guys have gone thru on the doorstep of the prince of darkness .